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#!/bin/sh
# Repeat a command to filter input several times
self=chn
# Check arguments.
if [ "$#" -lt 2 ] ; then
printf >&2 '%s: Need a count and a program name\n' "$self"
exit 2
fi
# Shift off the repetition count.
c=$1
shift
# Check the repetition count looks sane. Zero is fine!
if [ "$c" -lt 0 ] ; then
printf >&2 '%s: Nonsensical negative count\n' "$self"
exit 2
fi
# If the count is zero, just run the input straight through!
if [ "$c" -eq 0 ] ; then
cat
exit
fi
# Create a temporary directory with name in $td, and handle POSIX-ish traps to
# remove it when the script exits.
td=
cleanup() {
[ -n "$td" ] && rm -fr -- "$td"
if [ "$1" != EXIT ] ; then
trap - "$1"
kill "-$1" "$$"
fi
}
for sig in EXIT HUP INT TERM ; do
# shellcheck disable=SC2064
trap "cleanup $sig" "$sig"
done
td=$(mktd "$self") || exit
# Define and create input and output files
if=$td/if of=$td/of
touch -- "$if" "$of"
# Iterate through the count
while [ "${n=1}" -le "$c" ] ; do
# Start a subshell so we can deal with FDs cleanly
(
# If this isn't the first iteration, our input comes from $if
[ "$n" -eq 1 ] ||
exec <"$if"
# If this isn't the last iteration, our output goes to $of
[ "$n" -eq "$c" ] ||
exec >"$of"
# Run the command with the descriptors above; if the command fails, the
# subshell will exit, which will in turn exit the program
"$@"
) || exit
# Copy the output file over the input one
cp -- "$of" "$if"
# Increment the counter for the next while loop run
n=$((n+1))
done
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