#!/bin/sh

# overwrite: copy standard input to output after EOF.
# From ``The UNIX Programming Environment'' by Kernighan & Pike

opath=$PATH
PATH=/bin:/usr/bin

case $# in
    0|1) echo 'Usage: overwrite file cmd [args]' 1>&2; exit 2
esac

file=$1; shift
new=/tmp/overwr1.$$; old=/tmp/overwr2.$$
trap 'rm -f $new $old; exit 1' 1 2 15 # Clean up files.

if PATH=$opath "$@" >$new             # Collect input.
then
    cp $file $old                     # Save original file.
    trap '' 1 2 15                    # We are committed; ignore signals
    cp $new $file
else
    echo "overwrite: $1 failed, $file unchanged." 1>&2
    exit 1
fi

rm -f $new $old