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#!/bin/sh
# usage: ifchange target temporary

set -e
timestamp=
keepsuffix=
empty=
until [ $# -eq 0 ]; do
    case "$1" in
        --timestamp)
            timestamp=.
            ;;
        --timestamp=*)
            timestamp=`expr \( "$1" : '[^=]*=\(.*\)' \)`
            ;;
        --keep)
            keepsuffix=.old
            ;;
        --keep=*)
            keepsuffix=`expr \( "$1" : '[^=]*=\(.*\)' \)`
            ;;
        --empty)
            empty=yes
            ;;
        *)
            break
            ;;
    esac
    shift
done

target="$1"
temp="$2"
if [ "$temp" = - ]; then
    temp="tmpdata$$.tmp~"
    cat > "$temp" || exit $?
    trap 'rm -f "$temp"' 0
fi

if [ -f "$target" -a ! -${empty:+f}${empty:-s} "$temp" ] || cmp "$target" "$temp" >/dev/null 2>&1; then
    echo "$target unchanged"
    rm -f "$temp"
else
    echo "$target updated"
    [ x"${keepsuffix}" = x ] || mv -f "$target" "${target}${keepsuffix}"
    mv -f "$temp" "$target"
fi

if [ -n "${timestamp}" ]; then
    if [ x"${timestamp}" = x. ]; then
        case "$target" in
            */*)
                timestamp=`dirname "$target"`/.time.`basename "$target"`
                ;;
            *)
                timestamp=.time."$target"
                ;;
        esac
    fi
    : > "$timestamp"
fi