Is there a "watch" / "monitor" / "guard" program for Makefile dependencies?

Question

I've recently been spoiled by using nodemon in a terminal window, to run my Node.js program whenever I save a change.

I would like to do something similar with some C++ code I have. My actual project has lots of source files, but if we assume the following example, I would like to run make automatically whenever I save a change to sample.dat, program.c or header.h.

test: program sample.dat
    ./program < sample.dat

program: program.c header.h
    gcc program.c -o program

Is there an existing solution which does this?

(Without firing up an IDE. I know lots of IDEs can do a project rebuild when you change files.)

Answer 1

If you are on a platform that supports inotifywait (to my knowledge, only Linux; but since you asked about Make, it seems there's a good chance you're on Linux; for OS X, see this question), you can do something like this:

inotifywait --exclude '.*\.swp|.*\.o|.*~' --event MODIFY -q -m -r . |
while read
do make
done

Breaking that down:

inotifywait

Listen for file system events.

--exclude '.*\.swp|.*\.o|.*~'

Exclude files that end in .swp, .o or ~ (you'll probably want to add to this list).

--event MODIFY

When you find one print out the filepath of the file for which the event occurred.

-q

Do not print startup messages (so make is not prematurely invoked).

-m

Listen continuously.

-r .

Listen recursively on the current directory. Then it is piped into a simple loop which invokes make for every line read.

Tailor it to your needs. You may find inotifywait --help and the manpage helpful.

---

Here is a more detailed script. I haven't tested it much, so use with discernment. It is meant to keep the build from happening again and again needlessly, such as when switching branches in Git.

#!/bin/sh
datestampFormat="%Y%m%d%H%M%S"
lastrun=$(date +$datestampFormat)
inotifywait --exclude '.*\.swp|.*\.o|.*~' \
            --event MODIFY \
            --timefmt $datestampFormat \
            --format %T \
            -q -m -r . |
while read modified; do
    if [ $modified -gt $lastrun ]; then
        make
        lastrun=$(date +$datestampFormat)
    fi
done