A tool to run commands when files change.

Debounces change events, running the command only when no events
have arrived for some given time. This is useful since editors and
other programs often do a sequence of operations on files, producing
many events in rapid succession.

Waits for the subprocess to exit before it resumes watching.

Runs the command something like `$SHELL -c COMMAND CHANGED_FILES...`


usage: on-change [-d debounce] [-e eventmask] [-g glob]... FILES... CMD
    -d  debounce time. (default: 300ms)
    -e  event mask. (default: cwma)
        include these characters to listen for these events:
            c create
            w write
            r remove
            m rename (move)
            a chmod (access)
    -g  trigger events only when the file basename matches one of the given globs.


For example:
    $ on-change *.go 'go fmt'
    $ on-change -g '*.go' . 'go build'
    $ on-change -g '*.c' -g '*.h' src 'make'

In the first example the *.go glob will be expanded by the shell and only the existing
files that match will be watched. In the second example, the current directory will be
watched for file changes, and `on-change` will only run the command when the files that
changed match the glob passed. That is why it must be quoted.

Using the [es shell][1] the command can be a program fragment, which has nicer syntax:

    on-change *.c {
        cc -c $*
    }

    on-change *.o {
        cc -o foo *.o
    }


[1]: https://wryun.github.io/es-shell/