Watchman

This is an old script which I wrote for my personal needs and haven't used since a long time.

Answering for the sudden interest observed on HN. The name watchman seemd like a reasonable name for what this utlity does. I had no knowledge of existance of a similar utility by Facebook when I wrote this.

NAME

watchman - execute a command when something changes

SYNOPSIS

watchman [OPTIONS] <FILE PATTERNS> -- <COMMAND>
watchman [OPTIONS] <FILE NAME> <COMMAND>

DESCRIPTION

Execute a command as things change in file(s)/directory(s).

I have always wanted a watch tool which instead of being based on time (the watch command) will be based on space (files). That is what watch watchman is.

It uses inotify tools to provide that functionality. Watchman just listens to what inotifywait (from inotify-tools package of your distribution) says and executes commands.

This basically provides a continuous execution system, while not having to set up a elaborate project configuration (say, when what you are working on is just a tiny script).

In case of bigger projects, you could also have a test suit which needs to be run when you edit a project file.

Watchman also takes special care of not cluttering the STDOUT. Only your actual command can write to STDOUT.

OPTIONS

 -h          Show detailed help
 -v          Verbose output
 -x PATTERN  Exclude files matching PATTERN (POSIX extended regular expression)
 -r          Watch files recursively
 -b          Beep when command execution fails

FILE PATTERNS

Space separated file names/patterns which are to be watched by 'watchman'. This can also be a directory, in which case, all the files will be watched for changes.

COMMAND

The command which is to be executed when a change is triggered. Since, watchman can watch multiple files, there are a few file placeholders available which will be filled in appropriately at execution time. To use a placeholder just write it in braces in your command. Eg: {dir_name}/{base_prefix}.out

PLACEHOLDERS

The following placeholders are available to be used in a command.

file
The relative path to the file from current directory. Eg: ./foo/bar/foobar.baz

base_name
The base name of the file. Eg: foobar.baz

dir_name
The relative path to the directory file is in. Eg: ./foo/bar/

base_prefix
The file name without the file extension. Eg: foobar

WATCHING SINGLE FILES

In case you only have a single file as watch target, the delimter '--' can be skipped.

INSTALL

• Checkout cd to the the source code.

• To install, run make install.

• To uninstall, run make uninstall.

• If you are modifying watchman and want those changes to reflect automatically on next execution, then run: make develop. This just symlinks the script to the project directory.

• Available parameters:

  • PREFIX: Location of installation. (default: /usr/local/bin)
  • EXECUTABLE: Name of the executable file. (default: watchman)

EXAMPLES

• Watch a shell script and execute it on change.

   watchman sample.sh ./sample.sh
  

• Watch on the Haskell project under the current directory recursively and run Main.hs when anything is changed in it.

   watchman -r . -- runhaskell Main.hs
  

• Watch on a few Python scripts and execute a script which it changes. This uses the placeholder {file} to fill in the correct name. Give more verbose output since multiple files are being watched.

   watchman -v scripts/**/*.py -- python {file}
  

• Automatically build and execute a C file on change. This demonstrates the use of dir_name and base_prefix placeholders.

   watchman -vrb -x '.*.out' . -- 'gcc {file} -o {dir_name}/{base_prefix}.out && {dir_name}/{base_prefix}.out'
  

WHY THIS PROJECT?

• I badly needed a utility like this.
• I wanted to get my hands dirty with a proper bash based project and Makefiles.

TODO

• Support for long running processes. Eg. Reboot a web server. This will be useful in cases where corresponding server tool does not provide an option to auto-reload.
• Cycle through output colors in subsequent runs.
• Real MAN pages, instead of MAN like README doc.