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#!/bin/sh
# Create a temporary directory, sort of like mktemp -d does.
# Usage: mkdtemp /tmp phoey.XXXXXXXXXX
# First, try to use the mktemp program.
# Failing that, we'll roll our own mktemp-like function:
# - try to get random bytes from /dev/urandom
# - failing that, generate output from a combination of quickly-varying
# sources and gzip. Ignore non-varying gzip header, and extract
# "random" bits from there.
# - given those bits, map to file-name bytes using tr, and try to create
# the desired directory.
# - make only $MAX_TRIES attempts
ME=$(basename "$0")
die() { echo >&2 "$ME: $@"; exit 1; }
MAX_TRIES=4
rand_bytes()
{
n=$1
chars=abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789
dev_rand=/dev/urandom
if test -r "$dev_rand"; then
# Note: 256-length($chars) == 194; 3 copies of $chars is 186 + 8 = 194.
head -c$n "$dev_rand" | tr -c $chars 01234567$chars$chars$chars
return
fi
cmds='date; date +%N; free; who -a; w; ps auxww; ps ef; netstat -n'
data=$( (eval "$cmds") 2>&1 | gzip )
n_plus_50=$(expr $n + 50)
# Ensure that $data has length at least 50+$n
while :; do
len=$(echo "$data"|wc -c)
test $n_plus_50 -le $len && break;
data=$( (echo "$data"; eval "$cmds") 2>&1 | gzip )
done
echo "$data" \
| dd bs=1 skip=50 count=$n 2>/dev/null \
| tr -c $chars 01234567$chars$chars$chars
}
mkdtemp()
{
case $# in
2);;
*) die "Usage: $ME DIR TEMPLATE";;
esac
destdir=$1
template=$2
case $template in
*XXXX) ;;
*) die "invalid template: $template (must have a suffix of at least 4 X's)";;
esac
fail=0
# First, try to use mktemp.
d=$(env -u TMPDIR mktemp -d -t -p "$destdir" "$template" 2>/dev/null) \
|| fail=1
# The resulting name must be in the specified directory.
case $d in "$destdir"*);; *) fail=1;; esac
# It must have created the directory.
test -d "$d" || fail=1
# It must have 0700 permissions.
perms=$(ls -dgo "$d" 2>/dev/null) || fail=1
case $perms in drwx------*) ;; *) fail=1;; esac
test $fail = 0 && {
echo "$d"
return
}
# If we reach this point, we'll have to create a directory manually.
# Get a copy of the template without its suffix of X's.
base_template=$(echo "$template"|sed 's/XX*$//')
# Calculate how many X's we've just removed.
nx=$(expr length "$template" - length "$base_template")
err=
i=1
while :; do
X=$(rand_bytes $nx)
candidate_dir="$destdir/$base_template$X"
err=$(mkdir -m 0700 "$candidate_dir" 2>&1) \
&& { echo "$candidate_dir"; return; }
test $MAX_TRIES -le $i && break;
i=$(expr $i + 1)
done
die "$err"
}
mkdtemp "$@"
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