dirwatch

#!/bin/sh 
#
# NAME
#         dirwatch - run command on file modification
#
# SYNOPSIS
#         dirwatch [-m marker] command dir ...
#
# DESCRIPTION
#         dirwatch uses a touch file to track whether files
#         in a list of directories are modified. In the case
#         where there are no modified files, it will exit. In
#         the case where there are modified files it will 
#         execute the specified command.
#
#         Executing dirwatch will execute the check once only,
#         combine with the `watch` command to check repeatedly.
# 
# LIMITATIONS
#         dirwatch currently has very primitive command line
#         argument handling, so if the command has any arguments
#         they entire command line (including arguments) must be
#         quoted.
#
# EXAMPLES
#         Saying hello world if a file has been modified:
#             $ dirwatch "echo hello world" some/directory
#
#         Running make when a file is modified, using watch
#         to repeat every 2 seconds:
#             $ watch dirwatch make some/directory
#
#

if [ "$1" = "-m" ]; then
    marker="$2"; shift; shift
else 
    marker=.marker
fi

if [ $# -lt 2 ]; then
    echo "usage: `basename $0` [-m marker] command dir ..." >&2
    exit 1
fi

command="$1"; shift

if [ -f "$marker" ]; then
    changed=`find "$@" -newer $marker | wc -l`
    if [ "$changed" -ne 0 ]; then
        echo "[$changed] files have been updated - executing command." 
        touch "$marker"
        exec $command
    else
        echo "[0] files have been updated." 
    fi
else
    echo "no marker [$marker] - executing command." 
    touch "$marker"
    exec $command
fi