summaryrefslogtreecommitdiff
path: root/Master/tlpkg/tlperl/lib/IPC/Cmd.pm
blob: a42c21b84ee1bbd95ba2a6e5466066c410248a7b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
package IPC::Cmd;

use strict;

BEGIN {

    use constant IS_VMS         => $^O eq 'VMS'                       ? 1 : 0;
    use constant IS_WIN32       => $^O eq 'MSWin32'                   ? 1 : 0;
    use constant IS_WIN98       => (IS_WIN32 and !Win32::IsWinNT())   ? 1 : 0;
    use constant ALARM_CLASS    => __PACKAGE__ . '::TimeOut';
    use constant SPECIAL_CHARS  => qw[< > | &];
    use constant QUOTE          => do { IS_WIN32 ? q["] : q['] };

    use Exporter    ();
    use vars        qw[ @ISA $VERSION @EXPORT_OK $VERBOSE $DEBUG
                        $USE_IPC_RUN $USE_IPC_OPEN3 $CAN_USE_RUN_FORKED $WARN
                        $INSTANCES $ALLOW_NULL_ARGS
                        $HAVE_MONOTONIC
                    ];

    $VERSION        = '1.00';
    $VERBOSE        = 0;
    $DEBUG          = 0;
    $WARN           = 1;
    $USE_IPC_RUN    = IS_WIN32 && !IS_WIN98;
    $USE_IPC_OPEN3  = not IS_VMS;
    $ALLOW_NULL_ARGS = 0;

    $CAN_USE_RUN_FORKED = 0;
    eval {
        require POSIX; POSIX->import();
        require IPC::Open3; IPC::Open3->import();
        require IO::Select; IO::Select->import();
        require IO::Handle; IO::Handle->import();
        require FileHandle; FileHandle->import();
        require Socket;
        require Time::HiRes; Time::HiRes->import();
        require Win32 if IS_WIN32;
    };
    $CAN_USE_RUN_FORKED = $@ || !IS_VMS && !IS_WIN32;

    eval {
        my $wait_start_time = Time::HiRes::clock_gettime(&Time::HiRes::CLOCK_MONOTONIC);
    };
    if ($@) {
        $HAVE_MONOTONIC = 0;
    }
    else {
        $HAVE_MONOTONIC = 1;
    }

    @ISA            = qw[Exporter];
    @EXPORT_OK      = qw[can_run run run_forked QUOTE];
}

require Carp;
use File::Spec;
use Params::Check               qw[check];
use Text::ParseWords            ();             # import ONLY if needed!
use Module::Load::Conditional   qw[can_load];
use Locale::Maketext::Simple    Style => 'gettext';

local $Module::Load::Conditional::FORCE_SAFE_INC = 1;

=pod

=head1 NAME

IPC::Cmd - finding and running system commands made easy

=head1 SYNOPSIS

    use IPC::Cmd qw[can_run run run_forked];

    my $full_path = can_run('wget') or warn 'wget is not installed!';

    ### commands can be arrayrefs or strings ###
    my $cmd = "$full_path -b theregister.co.uk";
    my $cmd = [$full_path, '-b', 'theregister.co.uk'];

    ### in scalar context ###
    my $buffer;
    if( scalar run( command => $cmd,
                    verbose => 0,
                    buffer  => \$buffer,
                    timeout => 20 )
    ) {
        print "fetched webpage successfully: $buffer\n";
    }


    ### in list context ###
    my( $success, $error_message, $full_buf, $stdout_buf, $stderr_buf ) =
            run( command => $cmd, verbose => 0 );

    if( $success ) {
        print "this is what the command printed:\n";
        print join "", @$full_buf;
    }

    ### run_forked example ###
    my $result = run_forked("$full_path -q -O - theregister.co.uk", {'timeout' => 20});
    if ($result->{'exit_code'} eq 0 && !$result->{'timeout'}) {
        print "this is what wget returned:\n";
        print $result->{'stdout'};
    }

    ### check for features
    print "IPC::Open3 available: "  . IPC::Cmd->can_use_ipc_open3;
    print "IPC::Run available: "    . IPC::Cmd->can_use_ipc_run;
    print "Can capture buffer: "    . IPC::Cmd->can_capture_buffer;

    ### don't have IPC::Cmd be verbose, ie don't print to stdout or
    ### stderr when running commands -- default is '0'
    $IPC::Cmd::VERBOSE = 0;


=head1 DESCRIPTION

IPC::Cmd allows you to run commands platform independently,
interactively if desired, but have them still work.

The C<can_run> function can tell you if a certain binary is installed
and if so where, whereas the C<run> function can actually execute any
of the commands you give it and give you a clear return value, as well
as adhere to your verbosity settings.

=head1 CLASS METHODS

=head2 $ipc_run_version = IPC::Cmd->can_use_ipc_run( [VERBOSE] )

Utility function that tells you if C<IPC::Run> is available.
If the C<verbose> flag is passed, it will print diagnostic messages
if L<IPC::Run> can not be found or loaded.

=cut


sub can_use_ipc_run     {
    my $self    = shift;
    my $verbose = shift || 0;

    ### IPC::Run doesn't run on win98
    return if IS_WIN98;

    ### if we don't have ipc::run, we obviously can't use it.
    return unless can_load(
                        modules => { 'IPC::Run' => '0.55' },
                        verbose => ($WARN && $verbose),
                    );

    ### otherwise, we're good to go
    return $IPC::Run::VERSION;
}

=head2 $ipc_open3_version = IPC::Cmd->can_use_ipc_open3( [VERBOSE] )

Utility function that tells you if C<IPC::Open3> is available.
If the verbose flag is passed, it will print diagnostic messages
if C<IPC::Open3> can not be found or loaded.

=cut


sub can_use_ipc_open3   {
    my $self    = shift;
    my $verbose = shift || 0;

    ### IPC::Open3 is not working on VMS because of a lack of fork.
    return if IS_VMS;

    ### IPC::Open3 works on every non-VMS platform, but it can't
    ### capture buffers on win32 :(
    return unless can_load(
        modules => { map {$_ => '0.0'} qw|IPC::Open3 IO::Select Symbol| },
        verbose => ($WARN && $verbose),
    );

    return $IPC::Open3::VERSION;
}

=head2 $bool = IPC::Cmd->can_capture_buffer

Utility function that tells you if C<IPC::Cmd> is capable of
capturing buffers in it's current configuration.

=cut

sub can_capture_buffer {
    my $self    = shift;

    return 1 if $USE_IPC_RUN    && $self->can_use_ipc_run;
    return 1 if $USE_IPC_OPEN3  && $self->can_use_ipc_open3;
    return;
}

=head2 $bool = IPC::Cmd->can_use_run_forked

Utility function that tells you if C<IPC::Cmd> is capable of
providing C<run_forked> on the current platform.

=head1 FUNCTIONS

=head2 $path = can_run( PROGRAM );

C<can_run> takes only one argument: the name of a binary you wish
to locate. C<can_run> works much like the unix binary C<which> or the bash
command C<type>, which scans through your path, looking for the requested
binary.

Unlike C<which> and C<type>, this function is platform independent and
will also work on, for example, Win32.

If called in a scalar context it will return the full path to the binary
you asked for if it was found, or C<undef> if it was not.

If called in a list context and the global variable C<$INSTANCES> is a true
value, it will return a list of the full paths to instances
of the binary where found in C<PATH>, or an empty list if it was not found.

=cut

sub can_run {
    my $command = shift;

    # a lot of VMS executables have a symbol defined
    # check those first
    if ( $^O eq 'VMS' ) {
        require VMS::DCLsym;
        my $syms = VMS::DCLsym->new;
        return $command if scalar $syms->getsym( uc $command );
    }

    require File::Spec;
    require ExtUtils::MakeMaker;

    my @possibles;

    if( File::Spec->file_name_is_absolute($command) ) {
        return MM->maybe_command($command);

    } else {
        for my $dir (
            File::Spec->path,
            ( IS_WIN32 ? File::Spec->curdir : () )
        ) {
            next if ! $dir || ! -d $dir;
            my $abs = File::Spec->catfile( IS_WIN32 ? Win32::GetShortPathName( $dir ) : $dir, $command);
            push @possibles, $abs if $abs = MM->maybe_command($abs);
        }
    }
    return @possibles if wantarray and $INSTANCES;
    return shift @possibles;
}

=head2 $ok | ($ok, $err, $full_buf, $stdout_buff, $stderr_buff) = run( command => COMMAND, [verbose => BOOL, buffer => \$SCALAR, timeout => DIGIT] );

C<run> takes 4 arguments:

=over 4

=item command

This is the command to execute. It may be either a string or an array
reference.
This is a required argument.

See L<"Caveats"> for remarks on how commands are parsed and their
limitations.

=item verbose

This controls whether all output of a command should also be printed
to STDOUT/STDERR or should only be trapped in buffers (NOTE: buffers
require L<IPC::Run> to be installed, or your system able to work with
L<IPC::Open3>).

It will default to the global setting of C<$IPC::Cmd::VERBOSE>,
which by default is 0.

=item buffer

This will hold all the output of a command. It needs to be a reference
to a scalar.
Note that this will hold both the STDOUT and STDERR messages, and you
have no way of telling which is which.
If you require this distinction, run the C<run> command in list context
and inspect the individual buffers.

Of course, this requires that the underlying call supports buffers. See
the note on buffers above.

=item timeout

Sets the maximum time the command is allowed to run before aborting,
using the built-in C<alarm()> call. If the timeout is triggered, the
C<errorcode> in the return value will be set to an object of the
C<IPC::Cmd::TimeOut> class. See the L<"error message"> section below for
details.

Defaults to C<0>, meaning no timeout is set.

=back

C<run> will return a simple C<true> or C<false> when called in scalar
context.
In list context, you will be returned a list of the following items:

=over 4

=item success

A simple boolean indicating if the command executed without errors or
not.

=item error message

If the first element of the return value (C<success>) was 0, then some
error occurred. This second element is the error message the command
you requested exited with, if available. This is generally a pretty
printed value of C<$?> or C<$@>. See C<perldoc perlvar> for details on
what they can contain.
If the error was a timeout, the C<error message> will be prefixed with
the string C<IPC::Cmd::TimeOut>, the timeout class.

=item full_buffer

This is an array reference containing all the output the command
generated.
Note that buffers are only available if you have L<IPC::Run> installed,
or if your system is able to work with L<IPC::Open3> -- see below).
Otherwise, this element will be C<undef>.

=item out_buffer

This is an array reference containing all the output sent to STDOUT the
command generated. The notes from L<"full_buffer"> apply.

=item error_buffer

This is an arrayreference containing all the output sent to STDERR the
command generated. The notes from L<"full_buffer"> apply.


=back

See the L<"HOW IT WORKS"> section below to see how C<IPC::Cmd> decides
what modules or function calls to use when issuing a command.

=cut

{   my @acc = qw[ok error _fds];

    ### autogenerate accessors ###
    for my $key ( @acc ) {
        no strict 'refs';
        *{__PACKAGE__."::$key"} = sub {
            $_[0]->{$key} = $_[1] if @_ > 1;
            return $_[0]->{$key};
        }
    }
}

sub can_use_run_forked {
    return $CAN_USE_RUN_FORKED eq "1";
}

sub get_monotonic_time {
    if ($HAVE_MONOTONIC) {
        return Time::HiRes::clock_gettime(&Time::HiRes::CLOCK_MONOTONIC);
    }
    else {
        return time();
    }
}

sub adjust_monotonic_start_time {
    my ($ref_vars, $now, $previous) = @_;

    # workaround only for those systems which don't have
    # Time::HiRes::CLOCK_MONOTONIC (Mac OSX in particular)
    return if $HAVE_MONOTONIC;

    # don't have previous monotonic value (only happens once
    # in the beginning of the program execution)
    return unless $previous;

    my $time_diff = $now - $previous;

    # adjust previously saved time with the skew value which is
    # either negative when clock moved back or more than 5 seconds --
    # assuming that event loop does happen more often than once
    # per five seconds, which might not be always true (!) but
    # hopefully that's ok, because it's just a workaround
    if ($time_diff > 5 || $time_diff < 0) {
        foreach my $ref_var (@{$ref_vars}) {
            if (defined($$ref_var)) {
                $$ref_var = $$ref_var + $time_diff;
            }
        }
    }
}

sub uninstall_signals {
		return unless defined($IPC::Cmd::{'__old_signals'});

		foreach my $sig_name (keys %{$IPC::Cmd::{'__old_signals'}}) {
				$SIG{$sig_name} = $IPC::Cmd::{'__old_signals'}->{$sig_name};
		}
}

# incompatible with POSIX::SigAction
#
sub install_layered_signal {
  my ($s, $handler_code) = @_;

  my %available_signals = map {$_ => 1} keys %SIG;

  Carp::confess("install_layered_signal got nonexistent signal name [$s]")
    unless defined($available_signals{$s});
  Carp::confess("install_layered_signal expects coderef")
    if !ref($handler_code) || ref($handler_code) ne 'CODE';

  $IPC::Cmd::{'__old_signals'} = {}
  		unless defined($IPC::Cmd::{'__old_signals'});
	$IPC::Cmd::{'__old_signals'}->{$s} = $SIG{$s};

  my $previous_handler = $SIG{$s};

  my $sig_handler = sub {
    my ($called_sig_name, @sig_param) = @_;

    # $s is a closure referring to real signal name
    # for which this handler is being installed.
    # it is used to distinguish between
    # real signal handlers and aliased signal handlers
    my $signal_name = $s;

    # $called_sig_name is a signal name which
    # was passed to this signal handler;
    # it doesn't equal $signal_name in case
    # some signal handlers in %SIG point
    # to other signal handler (CHLD and CLD,
    # ABRT and IOT)
    #
    # initial signal handler for aliased signal
    # calls some other signal handler which
    # should not execute the same handler_code again
    if ($called_sig_name eq $signal_name) {
      $handler_code->($signal_name);
    }

    # run original signal handler if any (including aliased)
    #
    if (ref($previous_handler)) {
      $previous_handler->($called_sig_name, @sig_param);
    }
  };

  $SIG{$s} = $sig_handler;
}

# give process a chance sending TERM,
# waiting for a while (2 seconds)
# and killing it with KILL
sub kill_gently {
  my ($pid, $opts) = @_;

  require POSIX;

  $opts = {} unless $opts;
  $opts->{'wait_time'} = 2 unless defined($opts->{'wait_time'});
  $opts->{'first_kill_type'} = 'just_process' unless $opts->{'first_kill_type'};
  $opts->{'final_kill_type'} = 'just_process' unless $opts->{'final_kill_type'};

  if ($opts->{'first_kill_type'} eq 'just_process') {
    kill(15, $pid);
  }
  elsif ($opts->{'first_kill_type'} eq 'process_group') {
    kill(-15, $pid);
  }

  my $do_wait = 1;
  my $child_finished = 0;

  my $wait_start_time = get_monotonic_time();
  my $now;
  my $previous_monotonic_value;

  while ($do_wait) {
    $previous_monotonic_value = $now;
    $now = get_monotonic_time();
    
    adjust_monotonic_start_time([\$wait_start_time], $now, $previous_monotonic_value);

    if ($now > $wait_start_time + $opts->{'wait_time'}) {
        $do_wait = 0;
        next;
    }

    my $waitpid = waitpid($pid, POSIX::WNOHANG);

    if ($waitpid eq -1) {
        $child_finished = 1;
        $do_wait = 0;
        next;
    }
    
    Time::HiRes::usleep(250000); # quarter of a second
  }

  if (!$child_finished) {
    if ($opts->{'final_kill_type'} eq 'just_process') {
      kill(9, $pid);
    }
    elsif ($opts->{'final_kill_type'} eq 'process_group') {
      kill(-9, $pid);
    }
  }
}

sub open3_run {
    my ($cmd, $opts) = @_;

    $opts = {} unless $opts;

    my $child_in = FileHandle->new;
    my $child_out = FileHandle->new;
    my $child_err = FileHandle->new;
    $child_out->autoflush(1);
    $child_err->autoflush(1);

    my $pid = open3($child_in, $child_out, $child_err, $cmd);
    Time::HiRes::usleep(1);

    # push my child's pid to our parent
    # so in case i am killed parent
    # could stop my child (search for
    # child_child_pid in parent code)
    if ($opts->{'parent_info'}) {
      my $ps = $opts->{'parent_info'};
      print $ps "spawned $pid\n";
    }

    if ($child_in && $child_out->opened && $opts->{'child_stdin'}) {
        # If the child process dies for any reason,
        # the next write to CHLD_IN is likely to generate
        # a SIGPIPE in the parent, which is fatal by default.
        # So you may wish to handle this signal.
        #
        # from http://perldoc.perl.org/IPC/Open3.html,
        # absolutely needed to catch piped commands errors.
        #
        local $SIG{'PIPE'} = sub { 1; };

        print $child_in $opts->{'child_stdin'};
    }
    close($child_in);

    my $child_output = {
        'out' => $child_out->fileno,
        'err' => $child_err->fileno,
        $child_out->fileno => {
            'parent_socket' => $opts->{'parent_stdout'},
            'scalar_buffer' => "",
            'child_handle' => $child_out,
            'block_size' => ($child_out->stat)[11] || 1024,
          },
        $child_err->fileno => {
            'parent_socket' => $opts->{'parent_stderr'},
            'scalar_buffer' => "",
            'child_handle' => $child_err,
            'block_size' => ($child_err->stat)[11] || 1024,
          },
        };

    my $select = IO::Select->new();
    $select->add($child_out, $child_err);

    # pass any signal to the child
    # effectively creating process
    # strongly attached to the child:
    # it will terminate only after child
    # has terminated (except for SIGKILL,
    # which is specially handled)
    SIGNAL: foreach my $s (keys %SIG) {
        next SIGNAL if $s eq '__WARN__' or $s eq '__DIE__'; # Skip and don't clobber __DIE__ & __WARN__
        my $sig_handler;
        $sig_handler = sub {
            kill("$s", $pid);
            $SIG{$s} = $sig_handler;
        };
        $SIG{$s} = $sig_handler;
    }

    my $child_finished = 0;

    my $real_exit;
    my $exit_value;

    while(!$child_finished) {

        # parent was killed otherwise we would have got
        # the same signal as parent and process it same way
        if (getppid() eq "1") {

          # end my process group with all the children
          # (i am the process group leader, so my pid
          # equals to the process group id)
          #
          # same thing which is done
          # with $opts->{'clean_up_children'}
          # in run_forked
          #
          kill(-9, $$);

          POSIX::_exit 1;
        }

        my $waitpid = waitpid($pid, POSIX::WNOHANG);

        # child finished, catch it's exit status
        if ($waitpid ne 0 && $waitpid ne -1) {
          $real_exit = $?;
          $exit_value = $? >> 8;
        }

        if ($waitpid eq -1) {
          $child_finished = 1;
        }


        my $ready_fds = [];
        push @{$ready_fds}, $select->can_read(1/100);

        READY_FDS: while (scalar(@{$ready_fds})) {
            my $fd = shift @{$ready_fds};
            $ready_fds = [grep {$_ ne $fd} @{$ready_fds}];

            my $str = $child_output->{$fd->fileno};
            Carp::confess("child stream not found: $fd") unless $str;

            my $data;
            my $count = $fd->sysread($data, $str->{'block_size'});

            if ($count) {
                if ($str->{'parent_socket'}) {
                    my $ph = $str->{'parent_socket'};
                    print $ph $data;
                }
                else {
                    $str->{'scalar_buffer'} .= $data;
                }
            }
            elsif ($count eq 0) {
                $select->remove($fd);
                $fd->close();
            }
            else {
                Carp::confess("error during sysread: " . $!);
            }

            push @{$ready_fds}, $select->can_read(1/100) if $child_finished;
        }

        Time::HiRes::usleep(1);
    }

    # since we've successfully reaped the child,
    # let our parent know about this.
    #
    if ($opts->{'parent_info'}) {
        my $ps = $opts->{'parent_info'};

        # child was killed, inform parent
        if ($real_exit & 127) {
          print $ps "$pid killed with " . ($real_exit & 127) . "\n";
        }

        print $ps "reaped $pid\n";
    }

    if ($opts->{'parent_stdout'} || $opts->{'parent_stderr'}) {
        return $exit_value;
    }
    else {
        return {
            'stdout' => $child_output->{$child_output->{'out'}}->{'scalar_buffer'},
            'stderr' => $child_output->{$child_output->{'err'}}->{'scalar_buffer'},
            'exit_code' => $exit_value,
            };
    }
}

=head2 $hashref = run_forked( COMMAND, { child_stdin => SCALAR, timeout => DIGIT, stdout_handler => CODEREF, stderr_handler => CODEREF} );

C<run_forked> is used to execute some program or a coderef,
optionally feed it with some input, get its return code
and output (both stdout and stderr into separate buffers).
In addition, it allows to terminate the program
if it takes too long to finish.

The important and distinguishing feature of run_forked
is execution timeout which at first seems to be
quite a simple task but if you think
that the program which you're spawning
might spawn some children itself (which
in their turn could do the same and so on)
it turns out to be not a simple issue.

C<run_forked> is designed to survive and
successfully terminate almost any long running task,
even a fork bomb in case your system has the resources
to survive during given timeout.

This is achieved by creating separate watchdog process
which spawns the specified program in a separate
process session and supervises it: optionally
feeds it with input, stores its exit code,
stdout and stderr, terminates it in case
it runs longer than specified.

Invocation requires the command to be executed or a coderef and optionally a hashref of options:

=over

=item C<timeout>

Specify in seconds how long to run the command before it is killed with SIG_KILL (9),
which effectively terminates it and all of its children (direct or indirect).

=item C<child_stdin>

Specify some text that will be passed into the C<STDIN> of the executed program.

=item C<stdout_handler>

Coderef of a subroutine to call when a portion of data is received on
STDOUT from the executing program.

=item C<stderr_handler>

Coderef of a subroutine to call when a portion of data is received on
STDERR from the executing program.

=item C<wait_loop_callback>

Coderef of a subroutine to call inside of the main waiting loop
(while C<run_forked> waits for the external to finish or fail).
It is useful to stop running external process before it ends
by itself, e.g.

  my $r = run_forked("some external command", {
	  'wait_loop_callback' => sub {
          if (condition) {
              kill(1, $$);
          }
	  },
	  'terminate_on_signal' => 'HUP',
	  });

Combined with C<stdout_handler> and C<stderr_handler> allows terminating
external command based on its output. Could also be used as a timer
without engaging with L<alarm> (signals).

Remember that this code could be called every millisecond (depending
on the output which external command generates), so try to make it
as lightweight as possible.

=item C<discard_output>

Discards the buffering of the standard output and standard errors for return by run_forked().
With this option you have to use the std*_handlers to read what the command outputs.
Useful for commands that send a lot of output.

=item C<terminate_on_parent_sudden_death>

Enable this option if you wish all spawned processes to be killed if the initially spawned
process (the parent) is killed or dies without waiting for child processes.

=back

C<run_forked> will return a HASHREF with the following keys:

=over

=item C<exit_code>

The exit code of the executed program.

=item C<timeout>

The number of seconds the program ran for before being terminated, or 0 if no timeout occurred.

=item C<stdout>

Holds the standard output of the executed command (or empty string if
there was no STDOUT output or if C<discard_output> was used; it's always defined!)

=item C<stderr>

Holds the standard error of the executed command (or empty string if
there was no STDERR output or if C<discard_output> was used; it's always defined!)

=item C<merged>

Holds the standard output and error of the executed command merged into one stream
(or empty string if there was no output at all or if C<discard_output> was used; it's always defined!)

=item C<err_msg>

Holds some explanation in the case of an error.

=back

=cut

sub run_forked {
    ### container to store things in
    my $self = bless {}, __PACKAGE__;

    if (!can_use_run_forked()) {
        Carp::carp("run_forked is not available: $CAN_USE_RUN_FORKED");
        return;
    }

    require POSIX;

    my ($cmd, $opts) = @_;
    if (ref($cmd) eq 'ARRAY') {
        $cmd = join(" ", @{$cmd});
    }

    if (!$cmd) {
        Carp::carp("run_forked expects command to run");
        return;
    }

    $opts = {} unless $opts;
    $opts->{'timeout'} = 0 unless $opts->{'timeout'};
    $opts->{'terminate_wait_time'} = 2 unless defined($opts->{'terminate_wait_time'});

    # turned on by default
    $opts->{'clean_up_children'} = 1 unless defined($opts->{'clean_up_children'});

    # sockets to pass child stdout to parent
    my $child_stdout_socket;
    my $parent_stdout_socket;

    # sockets to pass child stderr to parent
    my $child_stderr_socket;
    my $parent_stderr_socket;

    # sockets for child -> parent internal communication
    my $child_info_socket;
    my $parent_info_socket;

    socketpair($child_stdout_socket, $parent_stdout_socket, &Socket::AF_UNIX, &Socket::SOCK_STREAM, &Socket::PF_UNSPEC) ||
      Carp::confess ("socketpair: $!");
    socketpair($child_stderr_socket, $parent_stderr_socket, &Socket::AF_UNIX, &Socket::SOCK_STREAM, &Socket::PF_UNSPEC) ||
      Carp::confess ("socketpair: $!");
    socketpair($child_info_socket, $parent_info_socket, &Socket::AF_UNIX, &Socket::SOCK_STREAM, &Socket::PF_UNSPEC) ||
      Carp::confess ("socketpair: $!");

    $child_stdout_socket->autoflush(1);
    $parent_stdout_socket->autoflush(1);
    $child_stderr_socket->autoflush(1);
    $parent_stderr_socket->autoflush(1);
    $child_info_socket->autoflush(1);
    $parent_info_socket->autoflush(1);

    my $start_time = get_monotonic_time();

    my $pid;
    if ($pid = fork) {

      # we are a parent
      close($parent_stdout_socket);
      close($parent_stderr_socket);
      close($parent_info_socket);

      my $flags;

      # prepare sockets to read from child

      $flags = fcntl($child_stdout_socket, POSIX::F_GETFL, 0) || Carp::confess "can't fnctl F_GETFL: $!";
      $flags |= POSIX::O_NONBLOCK;
      fcntl($child_stdout_socket, POSIX::F_SETFL, $flags) || Carp::confess "can't fnctl F_SETFL: $!";

      $flags = fcntl($child_stderr_socket, POSIX::F_GETFL, 0) || Carp::confess "can't fnctl F_GETFL: $!";
      $flags |= POSIX::O_NONBLOCK;
      fcntl($child_stderr_socket, POSIX::F_SETFL, $flags) || Carp::confess "can't fnctl F_SETFL: $!";

      $flags = fcntl($child_info_socket, POSIX::F_GETFL, 0) || Carp::confess "can't fnctl F_GETFL: $!";
      $flags |= POSIX::O_NONBLOCK;
      fcntl($child_info_socket, POSIX::F_SETFL, $flags) || Carp::confess "can't fnctl F_SETFL: $!";

  #    print "child $pid started\n";

      my $child_output = {
        $child_stdout_socket->fileno => {
          'scalar_buffer' => "",
          'child_handle' => $child_stdout_socket,
          'block_size' => ($child_stdout_socket->stat)[11] || 1024,
          'protocol' => 'stdout',
          },
        $child_stderr_socket->fileno => {
          'scalar_buffer' => "",
          'child_handle' => $child_stderr_socket,
          'block_size' => ($child_stderr_socket->stat)[11] || 1024,
          'protocol' => 'stderr',
          },
        $child_info_socket->fileno => {
          'scalar_buffer' => "",
          'child_handle' => $child_info_socket,
          'block_size' => ($child_info_socket->stat)[11] || 1024,
          'protocol' => 'info',
          },
        };

      my $select = IO::Select->new();
      $select->add($child_stdout_socket, $child_stderr_socket, $child_info_socket);

      my $child_timedout = 0;
      my $child_finished = 0;
      my $child_stdout = '';
      my $child_stderr = '';
      my $child_merged = '';
      my $child_exit_code = 0;
      my $child_killed_by_signal = 0;
      my $parent_died = 0;

      my $last_parent_check = 0;
      my $got_sig_child = 0;
      my $got_sig_quit = 0;
      my $orig_sig_child = $SIG{'CHLD'};

      $SIG{'CHLD'} = sub { $got_sig_child = get_monotonic_time(); };

      if ($opts->{'terminate_on_signal'}) {
        install_layered_signal($opts->{'terminate_on_signal'}, sub { $got_sig_quit = time(); });
      }

      my $child_child_pid;
      my $now;
      my $previous_monotonic_value;

      while (!$child_finished) {
        $previous_monotonic_value = $now;
        $now = get_monotonic_time();

        adjust_monotonic_start_time([\$start_time, \$last_parent_check, \$got_sig_child], $now, $previous_monotonic_value);

        if ($opts->{'terminate_on_parent_sudden_death'}) {
          # check for parent once each five seconds
          if ($now > $last_parent_check + 5) {
            if (getppid() eq "1") {
              kill_gently ($pid, {
                'first_kill_type' => 'process_group',
                'final_kill_type' => 'process_group',
                'wait_time' => $opts->{'terminate_wait_time'}
                });
              $parent_died = 1;
            }

            $last_parent_check = $now;
          }
        }

        # user specified timeout
        if ($opts->{'timeout'}) {
          if ($now > $start_time + $opts->{'timeout'}) {
            kill_gently ($pid, {
              'first_kill_type' => 'process_group',
              'final_kill_type' => 'process_group',
              'wait_time' => $opts->{'terminate_wait_time'}
              });
            $child_timedout = 1;
          }
        }

        # give OS 10 seconds for correct return of waitpid,
        # kill process after that and finish wait loop;
        # shouldn't ever happen -- remove this code?
        if ($got_sig_child) {
          if ($now > $got_sig_child + 10) {
            print STDERR "waitpid did not return -1 for 10 seconds after SIG_CHLD, killing [$pid]\n";
            kill (-9, $pid);
            $child_finished = 1;
          }
        }

        if ($got_sig_quit) {
          kill_gently ($pid, {
            'first_kill_type' => 'process_group',
            'final_kill_type' => 'process_group',
            'wait_time' => $opts->{'terminate_wait_time'}
            });
          $child_finished = 1;
        }

        my $waitpid = waitpid($pid, POSIX::WNOHANG);

        # child finished, catch it's exit status
        if ($waitpid ne 0 && $waitpid ne -1) {
          $child_exit_code = $? >> 8;
        }

        if ($waitpid eq -1) {
          $child_finished = 1;
        }

        my $ready_fds = [];
        push @{$ready_fds}, $select->can_read(1/100);

        READY_FDS: while (scalar(@{$ready_fds})) {
          my $fd = shift @{$ready_fds};
          $ready_fds = [grep {$_ ne $fd} @{$ready_fds}];

          my $str = $child_output->{$fd->fileno};
          Carp::confess("child stream not found: $fd") unless $str;

          my $data = "";
          my $count = $fd->sysread($data, $str->{'block_size'});

          if ($count) {
              # extract all the available lines and store the rest in temporary buffer
              if ($data =~ /(.+\n)([^\n]*)/so) {
                  $data = $str->{'scalar_buffer'} . $1;
                  $str->{'scalar_buffer'} = $2 || "";
              }
              else {
                  $str->{'scalar_buffer'} .= $data;
                  $data = "";
              }
          }
          elsif ($count eq 0) {
            $select->remove($fd);
            $fd->close();
            if ($str->{'scalar_buffer'}) {
                $data = $str->{'scalar_buffer'} . "\n";
            }
          }
          else {
            Carp::confess("error during sysread on [$fd]: " . $!);
          }

          # $data contains only full lines (or last line if it was unfinished read
          # or now new-line in the output of the child); dat is processed
          # according to the "protocol" of socket
          if ($str->{'protocol'} eq 'info') {
            if ($data =~ /^spawned ([0-9]+?)\n(.*?)/so) {
              $child_child_pid = $1;
              $data = $2;
            }
            if ($data =~ /^reaped ([0-9]+?)\n(.*?)/so) {
              $child_child_pid = undef;
              $data = $2;
            }
            if ($data =~ /^[\d]+ killed with ([0-9]+?)\n(.*?)/so) {
              $child_killed_by_signal = $1;
              $data = $2;
            }

            # we don't expect any other data in info socket, so it's
            # some strange violation of protocol, better know about this
            if ($data) {
              Carp::confess("info protocol violation: [$data]");
            }
          }
          if ($str->{'protocol'} eq 'stdout') {
            if (!$opts->{'discard_output'}) {
              $child_stdout .= $data;
              $child_merged .= $data;
            }

            if ($opts->{'stdout_handler'} && ref($opts->{'stdout_handler'}) eq 'CODE') {
              $opts->{'stdout_handler'}->($data);
            }
          }
          if ($str->{'protocol'} eq 'stderr') {
            if (!$opts->{'discard_output'}) {
              $child_stderr .= $data;
              $child_merged .= $data;
            }

            if ($opts->{'stderr_handler'} && ref($opts->{'stderr_handler'}) eq 'CODE') {
              $opts->{'stderr_handler'}->($data);
            }
          }
 
          # process may finish (waitpid returns -1) before
          # we've read all of its output because of buffering;
          # so try to read all the way it is possible to read
          # in such case - this shouldn't be too much (unless
          # the buffer size is HUGE -- should introduce
          # another counter in such case, maybe later)
          #
          push @{$ready_fds}, $select->can_read(1/100) if $child_finished;
        }

        if ($opts->{'wait_loop_callback'} && ref($opts->{'wait_loop_callback'}) eq 'CODE') {
          $opts->{'wait_loop_callback'}->();
        }

        Time::HiRes::usleep(1);
      }

      # $child_pid_pid is not defined in two cases:
      #  * when our child was killed before
      #    it had chance to tell us the pid
      #    of the child it spawned. we can do
      #    nothing in this case :(
      #  * our child successfully reaped its child,
      #    we have nothing left to do in this case
      #
      # defined $child_pid_pid means child's child
      # has not died but nobody is waiting for it,
      # killing it brutally.
      #
      if ($child_child_pid) {
        kill_gently($child_child_pid);
      }

      # in case there are forks in child which
      # do not forward or process signals (TERM) correctly
      # kill whole child process group, effectively trying
      # not to return with some children or their parts still running
      #
      # to be more accurate -- we need to be sure
      # that this is process group created by our child
      # (and not some other process group with the same pgid,
      # created just after death of our child) -- fortunately
      # this might happen only when process group ids
      # are reused quickly (there are lots of processes
      # spawning new process groups for example)
      #
      if ($opts->{'clean_up_children'}) {
        kill(-9, $pid);
      }

  #    print "child $pid finished\n";

      close($child_stdout_socket);
      close($child_stderr_socket);
      close($child_info_socket);

      my $o = {
        'stdout' => $child_stdout,
        'stderr' => $child_stderr,
        'merged' => $child_merged,
        'timeout' => $child_timedout ? $opts->{'timeout'} : 0,
        'exit_code' => $child_exit_code,
        'parent_died' => $parent_died,
        'killed_by_signal' => $child_killed_by_signal,
        'child_pgid' => $pid,
        'cmd' => $cmd,
        };

      my $err_msg = '';
      if ($o->{'exit_code'}) {
        $err_msg .= "exited with code [$o->{'exit_code'}]\n";
      }
      if ($o->{'timeout'}) {
        $err_msg .= "ran more than [$o->{'timeout'}] seconds\n";
      }
      if ($o->{'parent_died'}) {
        $err_msg .= "parent died\n";
      }
      if ($o->{'stdout'} && !$opts->{'non_empty_stdout_ok'}) {
        $err_msg .= "stdout:\n" . $o->{'stdout'} . "\n";
      }
      if ($o->{'stderr'}) {
        $err_msg .= "stderr:\n" . $o->{'stderr'} . "\n";
      }
      if ($o->{'killed_by_signal'}) {
        $err_msg .= "killed by signal [" . $o->{'killed_by_signal'} . "]\n";
      }
      $o->{'err_msg'} = $err_msg;

      if ($orig_sig_child) {
        $SIG{'CHLD'} = $orig_sig_child;
      }
      else {
        delete($SIG{'CHLD'});
      }

      uninstall_signals();

      return $o;
    }
    else {
      Carp::confess("cannot fork: $!") unless defined($pid);

      # create new process session for open3 call,
      # so we hopefully can kill all the subprocesses
      # which might be spawned in it (except for those
      # which do setsid theirselves -- can't do anything
      # with those)

      POSIX::setsid() || Carp::confess("Error running setsid: " . $!);

      if ($opts->{'child_BEGIN'} && ref($opts->{'child_BEGIN'}) eq 'CODE') {
        $opts->{'child_BEGIN'}->();
      }

      close($child_stdout_socket);
      close($child_stderr_socket);
      close($child_info_socket);

      my $child_exit_code;

      # allow both external programs
      # and internal perl calls
      if (!ref($cmd)) {
        $child_exit_code = open3_run($cmd, {
          'parent_info' => $parent_info_socket,
          'parent_stdout' => $parent_stdout_socket,
          'parent_stderr' => $parent_stderr_socket,
          'child_stdin' => $opts->{'child_stdin'},
          });
      }
      elsif (ref($cmd) eq 'CODE') {
        # reopen STDOUT and STDERR for child code:
        # https://rt.cpan.org/Ticket/Display.html?id=85912
        open STDOUT, '>&', $parent_stdout_socket || Carp::confess("Unable to reopen STDOUT: $!\n");
        open STDERR, '>&', $parent_stderr_socket || Carp::confess("Unable to reopen STDERR: $!\n");

        $child_exit_code = $cmd->({
          'opts' => $opts,
          'parent_info' => $parent_info_socket,
          'parent_stdout' => $parent_stdout_socket,
          'parent_stderr' => $parent_stderr_socket,
          'child_stdin' => $opts->{'child_stdin'},
          });
      }
      else {
        print $parent_stderr_socket "Invalid command reference: " . ref($cmd) . "\n";
        $child_exit_code = 1;
      }

      close($parent_stdout_socket);
      close($parent_stderr_socket);
      close($parent_info_socket);

      if ($opts->{'child_END'} && ref($opts->{'child_END'}) eq 'CODE') {
        $opts->{'child_END'}->();
      }

      $| = 1;
      POSIX::_exit $child_exit_code;
    }
}

sub run {
    ### container to store things in
    my $self = bless {}, __PACKAGE__;

    my %hash = @_;

    ### if the user didn't provide a buffer, we'll store it here.
    my $def_buf = '';

    my($verbose,$cmd,$buffer,$timeout);
    my $tmpl = {
        verbose => { default  => $VERBOSE,  store => \$verbose },
        buffer  => { default  => \$def_buf, store => \$buffer },
        command => { required => 1,         store => \$cmd,
                     allow    => sub { !ref($_[0]) or ref($_[0]) eq 'ARRAY' },
        },
        timeout => { default  => 0,         store => \$timeout },
    };

    unless( check( $tmpl, \%hash, $VERBOSE ) ) {
        Carp::carp( loc( "Could not validate input: %1",
                         Params::Check->last_error ) );
        return;
    };

    $cmd = _quote_args_vms( $cmd ) if IS_VMS;

    ### strip any empty elements from $cmd if present
    if ( $ALLOW_NULL_ARGS ) {
      $cmd = [ grep { defined } @$cmd ] if ref $cmd;
    }
    else {
      $cmd = [ grep { defined && length } @$cmd ] if ref $cmd;
    }

    my $pp_cmd = (ref $cmd ? "@$cmd" : $cmd);
    print loc("Running [%1]...\n", $pp_cmd ) if $verbose;

    ### did the user pass us a buffer to fill or not? if so, set this
    ### flag so we know what is expected of us
    ### XXX this is now being ignored. in the future, we could add diagnostic
    ### messages based on this logic
    #my $user_provided_buffer = $buffer == \$def_buf ? 0 : 1;

    ### buffers that are to be captured
    my( @buffer, @buff_err, @buff_out );

    ### capture STDOUT
    my $_out_handler = sub {
        my $buf = shift;
        return unless defined $buf;

        print STDOUT $buf if $verbose;
        push @buffer,   $buf;
        push @buff_out, $buf;
    };

    ### capture STDERR
    my $_err_handler = sub {
        my $buf = shift;
        return unless defined $buf;

        print STDERR $buf if $verbose;
        push @buffer,   $buf;
        push @buff_err, $buf;
    };


    ### flag to indicate we have a buffer captured
    my $have_buffer = $self->can_capture_buffer ? 1 : 0;

    ### flag indicating if the subcall went ok
    my $ok;

    ### don't look at previous errors:
    local $?;
    local $@;
    local $!;

    ### we might be having a timeout set
    eval {
        local $SIG{ALRM} = sub { die bless sub {
            ALARM_CLASS .
            qq[: Command '$pp_cmd' aborted by alarm after $timeout seconds]
        }, ALARM_CLASS } if $timeout;
        alarm $timeout || 0;

        ### IPC::Run is first choice if $USE_IPC_RUN is set.
        if( !IS_WIN32 and $USE_IPC_RUN and $self->can_use_ipc_run( 1 ) ) {
            ### ipc::run handlers needs the command as a string or an array ref

            $self->_debug( "# Using IPC::Run. Have buffer: $have_buffer" )
                if $DEBUG;

            $ok = $self->_ipc_run( $cmd, $_out_handler, $_err_handler );

        ### since IPC::Open3 works on all platforms, and just fails on
        ### win32 for capturing buffers, do that ideally
        } elsif ( $USE_IPC_OPEN3 and $self->can_use_ipc_open3( 1 ) ) {

            $self->_debug("# Using IPC::Open3. Have buffer: $have_buffer")
                if $DEBUG;

            ### in case there are pipes in there;
            ### IPC::Open3 will call exec and exec will do the right thing

            my $method = IS_WIN32 ? '_open3_run_win32' : '_open3_run';

            $ok = $self->$method(
                                    $cmd, $_out_handler, $_err_handler, $verbose
                                );

        ### if we are allowed to run verbose, just dispatch the system command
        } else {
            $self->_debug( "# Using system(). Have buffer: $have_buffer" )
                if $DEBUG;
            $ok = $self->_system_run( $cmd, $verbose );
        }

        alarm 0;
    };

    ### restore STDIN after duping, or STDIN will be closed for
    ### this current perl process!
    $self->__reopen_fds( @{ $self->_fds} ) if $self->_fds;

    my $err;
    unless( $ok ) {
        ### alarm happened
        if ( $@ and ref $@ and $@->isa( ALARM_CLASS ) ) {
            $err = $@->();  # the error code is an expired alarm

        ### another error happened, set by the dispatchub
        } else {
            $err = $self->error;
        }
    }

    ### fill the buffer;
    $$buffer = join '', @buffer if @buffer;

    ### return a list of flags and buffers (if available) in list
    ### context, or just a simple 'ok' in scalar
    return wantarray
                ? $have_buffer
                    ? ($ok, $err, \@buffer, \@buff_out, \@buff_err)
                    : ($ok, $err )
                : $ok


}

sub _open3_run_win32 {
  my $self    = shift;
  my $cmd     = shift;
  my $outhand = shift;
  my $errhand = shift;

  require Socket;

  my $pipe = sub {
    socketpair($_[0], $_[1], &Socket::AF_UNIX, &Socket::SOCK_STREAM, &Socket::PF_UNSPEC)
        or return undef;
    shutdown($_[0], 1);  # No more writing for reader
    shutdown($_[1], 0);  # No more reading for writer
    return 1;
  };

  my $open3 = sub {
    local (*TO_CHLD_R,     *TO_CHLD_W);
    local (*FR_CHLD_R,     *FR_CHLD_W);
    local (*FR_CHLD_ERR_R, *FR_CHLD_ERR_W);

    $pipe->(*TO_CHLD_R,     *TO_CHLD_W    ) or die $^E;
    $pipe->(*FR_CHLD_R,     *FR_CHLD_W    ) or die $^E;
    $pipe->(*FR_CHLD_ERR_R, *FR_CHLD_ERR_W) or die $^E;

    my $pid = IPC::Open3::open3('>&TO_CHLD_R', '<&FR_CHLD_W', '<&FR_CHLD_ERR_W', @_);

    return ( $pid, *TO_CHLD_W, *FR_CHLD_R, *FR_CHLD_ERR_R );
  };

  $cmd = [ grep { defined && length } @$cmd ] if ref $cmd;
  $cmd = $self->__fix_cmd_whitespace_and_special_chars( $cmd );

  my ($pid, $to_chld, $fr_chld, $fr_chld_err) =
    $open3->( ( ref $cmd ? @$cmd : $cmd ) );

  my $in_sel  = IO::Select->new();
  my $out_sel = IO::Select->new();

  my %objs;

  $objs{ fileno( $fr_chld ) } = $outhand;
  $objs{ fileno( $fr_chld_err ) } = $errhand;
  $in_sel->add( $fr_chld );
  $in_sel->add( $fr_chld_err );

  close($to_chld);

  while ($in_sel->count() + $out_sel->count()) {
    my ($ins, $outs) = IO::Select::select($in_sel, $out_sel, undef);

    for my $fh (@$ins) {
        my $obj = $objs{ fileno($fh) };
        my $buf;
        my $bytes_read = sysread($fh, $buf, 64*1024 ); #, length($buf));
        if (!$bytes_read) {
            $in_sel->remove($fh);
        }
        else {
            $obj->( "$buf" );
        }
      }

      for my $fh (@$outs) {
      }
  }

  waitpid($pid, 0);

  ### some error occurred
  if( $? ) {
        $self->error( $self->_pp_child_error( $cmd, $? ) );
        $self->ok( 0 );
        return;
  } else {
        return $self->ok( 1 );
  }
}

sub _open3_run {
    my $self            = shift;
    my $cmd             = shift;
    my $_out_handler    = shift;
    my $_err_handler    = shift;
    my $verbose         = shift || 0;

    ### Following code are adapted from Friar 'abstracts' in the
    ### Perl Monastery (http://www.perlmonks.org/index.pl?node_id=151886).
    ### XXX that code didn't work.
    ### we now use the following code, thanks to theorbtwo

    ### define them beforehand, so we always have defined FH's
    ### to read from.
    use Symbol;
    my $kidout      = Symbol::gensym();
    my $kiderror    = Symbol::gensym();

    ### Dup the filehandle so we can pass 'our' STDIN to the
    ### child process. This stops us from having to pump input
    ### from ourselves to the childprocess. However, we will need
    ### to revive the FH afterwards, as IPC::Open3 closes it.
    ### We'll do the same for STDOUT and STDERR. It works without
    ### duping them on non-unix derivatives, but not on win32.
    my @fds_to_dup = ( IS_WIN32 && !$verbose
                            ? qw[STDIN STDOUT STDERR]
                            : qw[STDIN]
                        );
    $self->_fds( \@fds_to_dup );
    $self->__dup_fds( @fds_to_dup );

    ### pipes have to come in a quoted string, and that clashes with
    ### whitespace. This sub fixes up such commands so they run properly
    $cmd = $self->__fix_cmd_whitespace_and_special_chars( $cmd );

    ### don't stringify @$cmd, so spaces in filenames/paths are
    ### treated properly
    my $pid = eval {
        IPC::Open3::open3(
                    '<&STDIN',
                    (IS_WIN32 ? '>&STDOUT' : $kidout),
                    (IS_WIN32 ? '>&STDERR' : $kiderror),
                    ( ref $cmd ? @$cmd : $cmd ),
                );
    };

    ### open3 error occurred
    if( $@ and $@ =~ /^open3:/ ) {
        $self->ok( 0 );
        $self->error( $@ );
        return;
    };

    ### use OUR stdin, not $kidin. Somehow,
    ### we never get the input.. so jump through
    ### some hoops to do it :(
    my $selector = IO::Select->new(
                        (IS_WIN32 ? \*STDERR : $kiderror),
                        \*STDIN,
                        (IS_WIN32 ? \*STDOUT : $kidout)
                    );

    STDOUT->autoflush(1);   STDERR->autoflush(1);   STDIN->autoflush(1);
    $kidout->autoflush(1)   if UNIVERSAL::can($kidout,   'autoflush');
    $kiderror->autoflush(1) if UNIVERSAL::can($kiderror, 'autoflush');

    ### add an explicit break statement
    ### code courtesy of theorbtwo from #london.pm
    my $stdout_done = 0;
    my $stderr_done = 0;
    OUTER: while ( my @ready = $selector->can_read ) {

        for my $h ( @ready ) {
            my $buf;

            ### $len is the amount of bytes read
            my $len = sysread( $h, $buf, 4096 );    # try to read 4096 bytes

            ### see perldoc -f sysread: it returns undef on error,
            ### so bail out.
            if( not defined $len ) {
                warn(loc("Error reading from process: %1", $!));
                last OUTER;
            }

            ### check for $len. it may be 0, at which point we're
            ### done reading, so don't try to process it.
            ### if we would print anyway, we'd provide bogus information
            $_out_handler->( "$buf" ) if $len && $h == $kidout;
            $_err_handler->( "$buf" ) if $len && $h == $kiderror;

            ### Wait till child process is done printing to both
            ### stdout and stderr.
            $stdout_done = 1 if $h == $kidout   and $len == 0;
            $stderr_done = 1 if $h == $kiderror and $len == 0;
            last OUTER if ($stdout_done && $stderr_done);
        }
    }

    waitpid $pid, 0; # wait for it to die

    ### restore STDIN after duping, or STDIN will be closed for
    ### this current perl process!
    ### done in the parent call now
    # $self->__reopen_fds( @fds_to_dup );

    ### some error occurred
    if( $? ) {
        $self->error( $self->_pp_child_error( $cmd, $? ) );
        $self->ok( 0 );
        return;
    } else {
        return $self->ok( 1 );
    }
}

### Text::ParseWords::shellwords() uses unix semantics. that will break
### on win32
{   my $parse_sub = IS_WIN32
                        ? __PACKAGE__->can('_split_like_shell_win32')
                        : Text::ParseWords->can('shellwords');

    sub _ipc_run {
        my $self            = shift;
        my $cmd             = shift;
        my $_out_handler    = shift;
        my $_err_handler    = shift;

        STDOUT->autoflush(1); STDERR->autoflush(1);

        ### a command like:
        # [
        #     '/usr/bin/gzip',
        #     '-cdf',
        #     '/Users/kane/sources/p4/other/archive-extract/t/src/x.tgz',
        #     '|',
        #     '/usr/bin/tar',
        #     '-tf -'
        # ]
        ### needs to become:
        # [
        #     ['/usr/bin/gzip', '-cdf',
        #       '/Users/kane/sources/p4/other/archive-extract/t/src/x.tgz']
        #     '|',
        #     ['/usr/bin/tar', '-tf -']
        # ]


        my @command;
        my $special_chars;

        my $re = do { my $x = join '', SPECIAL_CHARS; qr/([$x])/ };
        if( ref $cmd ) {
            my $aref = [];
            for my $item (@$cmd) {
                if( $item =~ $re ) {
                    push @command, $aref, $item;
                    $aref = [];
                    $special_chars .= $1;
                } else {
                    push @$aref, $item;
                }
            }
            push @command, $aref;
        } else {
            @command = map { if( $_ =~ $re ) {
                                $special_chars .= $1; $_;
                             } else {
#                                [ split /\s+/ ]
                                 [ map { m/[ ]/ ? qq{'$_'} : $_ } $parse_sub->($_) ]
                             }
                        } split( /\s*$re\s*/, $cmd );
        }

        ### if there's a pipe in the command, *STDIN needs to
        ### be inserted *BEFORE* the pipe, to work on win32
        ### this also works on *nix, so we should do it when possible
        ### this should *also* work on multiple pipes in the command
        ### if there's no pipe in the command, append STDIN to the back
        ### of the command instead.
        ### XXX seems IPC::Run works it out for itself if you just
        ### don't pass STDIN at all.
        #     if( $special_chars and $special_chars =~ /\|/ ) {
        #         ### only add STDIN the first time..
        #         my $i;
        #         @command = map { ($_ eq '|' && not $i++)
        #                             ? ( \*STDIN, $_ )
        #                             : $_
        #                         } @command;
        #     } else {
        #         push @command, \*STDIN;
        #     }

        # \*STDIN is already included in the @command, see a few lines up
        my $ok = eval { IPC::Run::run(   @command,
                                fileno(STDOUT).'>',
                                $_out_handler,
                                fileno(STDERR).'>',
                                $_err_handler
                            )
                        };

        ### all is well
        if( $ok ) {
            return $self->ok( $ok );

        ### some error occurred
        } else {
            $self->ok( 0 );

            ### if the eval fails due to an exception, deal with it
            ### unless it's an alarm
            if( $@ and not UNIVERSAL::isa( $@, ALARM_CLASS ) ) {
                $self->error( $@ );

            ### if it *is* an alarm, propagate
            } elsif( $@ ) {
                die $@;

            ### some error in the sub command
            } else {
                $self->error( $self->_pp_child_error( $cmd, $? ) );
            }

            return;
        }
    }
}

sub _system_run {
    my $self    = shift;
    my $cmd     = shift;
    my $verbose = shift || 0;

    ### pipes have to come in a quoted string, and that clashes with
    ### whitespace. This sub fixes up such commands so they run properly
    $cmd = $self->__fix_cmd_whitespace_and_special_chars( $cmd );

    my @fds_to_dup = $verbose ? () : qw[STDOUT STDERR];
    $self->_fds( \@fds_to_dup );
    $self->__dup_fds( @fds_to_dup );

    ### system returns 'true' on failure -- the exit code of the cmd
    $self->ok( 1 );
    system( ref $cmd ? @$cmd : $cmd ) == 0 or do {
        $self->error( $self->_pp_child_error( $cmd, $? ) );
        $self->ok( 0 );
    };

    ### done in the parent call now
    #$self->__reopen_fds( @fds_to_dup );

    return unless $self->ok;
    return $self->ok;
}

{   my %sc_lookup = map { $_ => $_ } SPECIAL_CHARS;


    sub __fix_cmd_whitespace_and_special_chars {
        my $self = shift;
        my $cmd  = shift;

        ### command has a special char in it
        if( ref $cmd and grep { $sc_lookup{$_} } @$cmd ) {

            ### since we have special chars, we have to quote white space
            ### this *may* conflict with the parsing :(
            my $fixed;
            my @cmd = map { / / ? do { $fixed++; QUOTE.$_.QUOTE } : $_ } @$cmd;

            $self->_debug( "# Quoted $fixed arguments containing whitespace" )
                    if $DEBUG && $fixed;

            ### stringify it, so the special char isn't escaped as argument
            ### to the program
            $cmd = join ' ', @cmd;
        }

        return $cmd;
    }
}

### Command-line arguments (but not the command itself) must be quoted
### to ensure case preservation. Borrowed from Module::Build with adaptations.
### Patch for this supplied by Craig Berry, see RT #46288: [PATCH] Add argument
### quoting for run() on VMS
sub _quote_args_vms {
  ### Returns a command string with proper quoting so that the subprocess
  ### sees this same list of args, or if we get a single arg that is an
  ### array reference, quote the elements of it (except for the first)
  ### and return the reference.
  my @args = @_;
  my $got_arrayref = (scalar(@args) == 1
                      && UNIVERSAL::isa($args[0], 'ARRAY'))
                   ? 1
                   : 0;

  @args = split(/\s+/, $args[0]) unless $got_arrayref || scalar(@args) > 1;

  my $cmd = $got_arrayref ? shift @{$args[0]} : shift @args;

  ### Do not quote qualifiers that begin with '/' or previously quoted args.
  map { if (/^[^\/\"]/) {
          $_ =~ s/\"/""/g;     # escape C<"> by doubling
          $_ = q(").$_.q(");
        }
  }
    ($got_arrayref ? @{$args[0]}
                   : @args
    );

  $got_arrayref ? unshift(@{$args[0]}, $cmd) : unshift(@args, $cmd);

  return $got_arrayref ? $args[0]
                       : join(' ', @args);
}


### XXX this is cribbed STRAIGHT from M::B 0.30 here:
### http://search.cpan.org/src/KWILLIAMS/Module-Build-0.30/lib/Module/Build/Platform/Windows.pm:split_like_shell
### XXX this *should* be integrated into text::parsewords
sub _split_like_shell_win32 {
  # As it turns out, Windows command-parsing is very different from
  # Unix command-parsing.  Double-quotes mean different things,
  # backslashes don't necessarily mean escapes, and so on.  So we
  # can't use Text::ParseWords::shellwords() to break a command string
  # into words.  The algorithm below was bashed out by Randy and Ken
  # (mostly Randy), and there are a lot of regression tests, so we
  # should feel free to adjust if desired.

  local $_ = shift;

  my @argv;
  return @argv unless defined() && length();

  my $arg = '';
  my( $i, $quote_mode ) = ( 0, 0 );

  while ( $i < length() ) {

    my $ch      = substr( $_, $i  , 1 );
    my $next_ch = substr( $_, $i+1, 1 );

    if ( $ch eq '\\' && $next_ch eq '"' ) {
      $arg .= '"';
      $i++;
    } elsif ( $ch eq '\\' && $next_ch eq '\\' ) {
      $arg .= '\\';
      $i++;
    } elsif ( $ch eq '"' && $next_ch eq '"' && $quote_mode ) {
      $quote_mode = !$quote_mode;
      $arg .= '"';
      $i++;
    } elsif ( $ch eq '"' && $next_ch eq '"' && !$quote_mode &&
          ( $i + 2 == length()  ||
        substr( $_, $i + 2, 1 ) eq ' ' )
        ) { # for cases like: a"" => [ 'a' ]
      push( @argv, $arg );
      $arg = '';
      $i += 2;
    } elsif ( $ch eq '"' ) {
      $quote_mode = !$quote_mode;
    } elsif ( $ch eq ' ' && !$quote_mode ) {
      push( @argv, $arg ) if defined( $arg ) && length( $arg );
      $arg = '';
      ++$i while substr( $_, $i + 1, 1 ) eq ' ';
    } else {
      $arg .= $ch;
    }

    $i++;
  }

  push( @argv, $arg ) if defined( $arg ) && length( $arg );
  return @argv;
}



{   use File::Spec;
    use Symbol;

    my %Map = (
        STDOUT => [qw|>&|, \*STDOUT, Symbol::gensym() ],
        STDERR => [qw|>&|, \*STDERR, Symbol::gensym() ],
        STDIN  => [qw|<&|, \*STDIN,  Symbol::gensym() ],
    );

    ### dups FDs and stores them in a cache
    sub __dup_fds {
        my $self    = shift;
        my @fds     = @_;

        __PACKAGE__->_debug( "# Closing the following fds: @fds" ) if $DEBUG;

        for my $name ( @fds ) {
            my($redir, $fh, $glob) = @{$Map{$name}} or (
                Carp::carp(loc("No such FD: '%1'", $name)), next );

            ### MUST use the 2-arg version of open for dup'ing for
            ### 5.6.x compatibility. 5.8.x can use 3-arg open
            ### see perldoc5.6.2 -f open for details
            open $glob, $redir . fileno($fh) or (
                        Carp::carp(loc("Could not dup '$name': %1", $!)),
                        return
                    );

            ### we should re-open this filehandle right now, not
            ### just dup it
            ### Use 2-arg version of open, as 5.5.x doesn't support
            ### 3-arg version =/
            if( $redir eq '>&' ) {
                open( $fh, '>' . File::Spec->devnull ) or (
                    Carp::carp(loc("Could not reopen '$name': %1", $!)),
                    return
                );
            }
        }

        return 1;
    }

    ### reopens FDs from the cache
    sub __reopen_fds {
        my $self    = shift;
        my @fds     = @_;

        __PACKAGE__->_debug( "# Reopening the following fds: @fds" ) if $DEBUG;

        for my $name ( @fds ) {
            my($redir, $fh, $glob) = @{$Map{$name}} or (
                Carp::carp(loc("No such FD: '%1'", $name)), next );

            ### MUST use the 2-arg version of open for dup'ing for
            ### 5.6.x compatibility. 5.8.x can use 3-arg open
            ### see perldoc5.6.2 -f open for details
            open( $fh, $redir . fileno($glob) ) or (
                    Carp::carp(loc("Could not restore '$name': %1", $!)),
                    return
                );

            ### close this FD, we're not using it anymore
            close $glob;
        }
        return 1;

    }
}

sub _debug {
    my $self    = shift;
    my $msg     = shift or return;
    my $level   = shift || 0;

    local $Carp::CarpLevel += $level;
    Carp::carp($msg);

    return 1;
}

sub _pp_child_error {
    my $self    = shift;
    my $cmd     = shift or return;
    my $ce      = shift or return;
    my $pp_cmd  = ref $cmd ? "@$cmd" : $cmd;


    my $str;
    if( $ce == -1 ) {
        ### Include $! in the error message, so that the user can
        ### see 'No such file or directory' versus 'Permission denied'
        ### versus 'Cannot fork' or whatever the cause was.
        $str = "Failed to execute '$pp_cmd': $!";

    } elsif ( $ce & 127 ) {
        ### some signal
        $str = loc( "'%1' died with signal %2, %3 coredump",
               $pp_cmd, ($ce & 127), ($ce & 128) ? 'with' : 'without');

    } else {
        ### Otherwise, the command run but gave error status.
        $str = "'$pp_cmd' exited with value " . ($ce >> 8);
    }

    $self->_debug( "# Child error '$ce' translated to: $str" ) if $DEBUG;

    return $str;
}

1;

__END__

=head2 $q = QUOTE

Returns the character used for quoting strings on this platform. This is
usually a C<'> (single quote) on most systems, but some systems use different
quotes. For example, C<Win32> uses C<"> (double quote).

You can use it as follows:

  use IPC::Cmd qw[run QUOTE];
  my $cmd = q[echo ] . QUOTE . q[foo bar] . QUOTE;

This makes sure that C<foo bar> is treated as a string, rather than two
separate arguments to the C<echo> function.

=head1 HOW IT WORKS

C<run> will try to execute your command using the following logic:

=over 4

=item *

If you have C<IPC::Run> installed, and the variable C<$IPC::Cmd::USE_IPC_RUN>
is set to true (See the L<"Global Variables"> section) use that to execute
the command. You will have the full output available in buffers, interactive commands
are sure to work  and you are guaranteed to have your verbosity
settings honored cleanly.

=item *

Otherwise, if the variable C<$IPC::Cmd::USE_IPC_OPEN3> is set to true
(See the L<"Global Variables"> section), try to execute the command using
L<IPC::Open3>. Buffers will be available on all platforms,
interactive commands will still execute cleanly, and also your verbosity
settings will be adhered to nicely;

=item *

Otherwise, if you have the C<verbose> argument set to true, we fall back
to a simple C<system()> call. We cannot capture any buffers, but
interactive commands will still work.

=item *

Otherwise we will try and temporarily redirect STDERR and STDOUT, do a
C<system()> call with your command and then re-open STDERR and STDOUT.
This is the method of last resort and will still allow you to execute
your commands cleanly. However, no buffers will be available.

=back

=head1 Global Variables

The behaviour of IPC::Cmd can be altered by changing the following
global variables:

=head2 $IPC::Cmd::VERBOSE

This controls whether IPC::Cmd will print any output from the
commands to the screen or not. The default is 0.

=head2 $IPC::Cmd::USE_IPC_RUN

This variable controls whether IPC::Cmd will try to use L<IPC::Run>
when available and suitable.

=head2 $IPC::Cmd::USE_IPC_OPEN3

This variable controls whether IPC::Cmd will try to use L<IPC::Open3>
when available and suitable. Defaults to true.

=head2 $IPC::Cmd::WARN

This variable controls whether run-time warnings should be issued, like
the failure to load an C<IPC::*> module you explicitly requested.

Defaults to true. Turn this off at your own risk.

=head2 $IPC::Cmd::INSTANCES

This variable controls whether C<can_run> will return all instances of
the binary it finds in the C<PATH> when called in a list context.

Defaults to false, set to true to enable the described behaviour.

=head2 $IPC::Cmd::ALLOW_NULL_ARGS

This variable controls whether C<run> will remove any empty/null arguments
it finds in command arguments.

Defaults to false, so it will remove null arguments. Set to true to allow
them.

=head1 Caveats

=over 4

=item Whitespace and IPC::Open3 / system()

When using C<IPC::Open3> or C<system>, if you provide a string as the
C<command> argument, it is assumed to be appropriately escaped. You can
use the C<QUOTE> constant to use as a portable quote character (see above).
However, if you provide an array reference, special rules apply:

If your command contains B<special characters> (< > | &), it will
be internally stringified before executing the command, to avoid that these
special characters are escaped and passed as arguments instead of retaining
their special meaning.

However, if the command contained arguments that contained whitespace,
stringifying the command would lose the significance of the whitespace.
Therefore, C<IPC::Cmd> will quote any arguments containing whitespace in your
command if the command is passed as an arrayref and contains special characters.

=item Whitespace and IPC::Run

When using C<IPC::Run>, if you provide a string as the C<command> argument,
the string will be split on whitespace to determine the individual elements
of your command. Although this will usually just Do What You Mean, it may
break if you have files or commands with whitespace in them.

If you do not wish this to happen, you should provide an array
reference, where all parts of your command are already separated out.
Note however, if there are extra or spurious whitespaces in these parts,
the parser or underlying code may not interpret it correctly, and
cause an error.

Example:
The following code

    gzip -cdf foo.tar.gz | tar -xf -

should either be passed as

    "gzip -cdf foo.tar.gz | tar -xf -"

or as

    ['gzip', '-cdf', 'foo.tar.gz', '|', 'tar', '-xf', '-']

But take care not to pass it as, for example

    ['gzip -cdf foo.tar.gz', '|', 'tar -xf -']

Since this will lead to issues as described above.


=item IO Redirect

Currently it is too complicated to parse your command for IO
redirections. For capturing STDOUT or STDERR there is a work around
however, since you can just inspect your buffers for the contents.

=item Interleaving STDOUT/STDERR

Neither IPC::Run nor IPC::Open3 can interleave STDOUT and STDERR. For short
bursts of output from a program, e.g. this sample,

    for ( 1..4 ) {
        $_ % 2 ? print STDOUT $_ : print STDERR $_;
    }

IPC::[Run|Open3] will first read all of STDOUT, then all of STDERR, meaning
the output looks like '13' on STDOUT and '24' on STDERR, instead of

    1
    2
    3
    4

This has been recorded in L<rt.cpan.org> as bug #37532: Unable to interleave
STDOUT and STDERR.

=back

=head1 See Also

L<IPC::Run>, L<IPC::Open3>

=head1 ACKNOWLEDGEMENTS

Thanks to James Mastros and Martijn van der Streek for their
help in getting L<IPC::Open3> to behave nicely.

Thanks to Petya Kohts for the C<run_forked> code.

=head1 BUG REPORTS

Please report bugs or other issues to E<lt>bug-ipc-cmd@rt.cpan.orgE<gt>.

=head1 AUTHOR

Original author: Jos Boumans E<lt>kane@cpan.orgE<gt>.
Current maintainer: Chris Williams E<lt>bingos@cpan.orgE<gt>.

=head1 COPYRIGHT

This library is free software; you may redistribute and/or modify it
under the same terms as Perl itself.

=cut