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|
#!/bin/sh
set -eu
usage() {
cat <<-'EOF'
Usage:
ifnew [-v] FILE
ifnew -h
EOF
}
help() {
cat <<-'EOF'
Options:
-v notify when new
-h, --help show this message
FILE the target to compared against
Compare STDIN to FILE, and only write to FILE if STDIN content
differs from FILE content. When -v is given, notify on STDERR
that FILE has new content (useful for debugging purposes).
Examples:
Create a new file, don't update it afterwards, and update it
as the content changes:
$ echo aaa | ifnew new-file
$ stat --print='%y' new-file
# timestamp 1
$ echo aaa | ifnew new-file
$ stat --print='%y' new-file
# timestamp 1
$ echo bbb | ifnew new-file
$ stat --print='%y' new-file
# timestamp 2
Only change file when content changes in a Makefile, and print
to STDERR when it does:
i18.cfg: ALWAYS
gen-cfg | ifnew -v $@
po4a $@
EOF
}
for flag in "$@"; do
case "$flag" in
(--)
break
;;
(--help)
usage
help
exit
;;
(*)
;;
esac
done
VERBOSE=false
while getopts 'vh' flag; do
case "$flag" in
(v)
VERBOSE=true
;;
(h)
usage
help
exit
;;
(*)
usage >&2
exit 2
;;
esac
done
shift $((OPTIND - 1))
FILE="${1:-}"
eval "$(assert-arg -- "$FILE" 'FILE')"
STDIN="$FILE.$(uuid).tmp"
trap 'rm -f "$STDIN"' EXIT
cat - > "$STDIN"
if ! cmp -s "$STDIN" "$FILE"; then
MV_ARGS=''
if [ "$VERBOSE" = true ]; then
printf 'ifnew: "%s" will be updated.\n' "$FILE" >&2
MV_ARGS='-v'
fi
mv $MV_ARGS "$STDIN" "$FILE"
else
if [ "$VERBOSE" = true ]; then
printf 'ifnew: "%s" left unchanged.\n' "$FILE" >&2
rm -vf "$STDIN"
fi
fi
|
