This lets you write things in a loop like this: while true do However, any new files in the directory will cause entr to stop. With it you can use a directory name or a file name and the program will watch that directory along with any files. txt files changes, it will copy to /tmp/archive. For example: find /tmp/t/data -name '*.txt' | entr cp /_ /tmp/archive The /_ placeholder gets the name of the first file that caused a trigger, although that doesn’t seem to work properly with -s. -r – Kill previously run command before executing command.-p – Do not execute the command until an event occurs.-d – Track directories that do not start with “.”.-c – Clear screen before executing command.You’ll want it running in the foreground. So, unlike incron, entr is an interactive tool. Speaking of the keyboard, you can also press space to trigger the action manually, as though a file changed. Usually, you’ll stop with a Control+C or a “q” character. When you stop the program, that’s the end of it. As long as it is running, changes in the target files will trigger the specified action. With entr, the command runs like a normal application. That survives a reboot or anything else short of you canceling it. That is, it causes some action to occur any time the specified file system changes happen. As the name suggests, incron does for filesystem changes what cron does for time. It also makes things easier, although perhaps not as easy as entr.

I had mentioned incron before as a way to attach actions to file changes. If you can’t find entr, you can download it from the website.įrequently, you’ll feed the output from find or a similar command to entr.

Back in the first window (or your GUI editor) make some changes to the file and save it while observing the second window.

In the second window issue the command: echo '/tmp/foo' | entr wc /tmp/foo.

In one window, open your favorite editor to create an empty file named /tmp/foo and save it.

For example, try this after you install entr with your package manager. There are a handful of options we’ll talk about in a bit, but it is really that simple. It will then run a command and repeat it any time the input files change. It reads a list of file names on its standard input. It isn’t as versatile, but it is easy to use and covers a lot of common use cases where you want some action to occur when a file changes. But there was one very easy-to-use tool that didn’t show up, so I wanted to talk about it. The comments had a lot of alternative ways to do the same job, which is great. In an earlier installment of Linux Fu, I mentioned how you can use inotifywait to efficiently watch for file system changes.

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