kqwait

Waits for write, rename and delete events on files and file creation and deletion events in directories and returns. Please note, that simply touching a file will not trigger a return.

Supports waiting on multiple files and directories. When waiting on a directory, adding a file, or deleting a file will trigger a return. Everything else (like touching or writing) will not trigger a return.

This tool is inspired by inotifywait, the original kqueue paper, and the lack of anything similar (to the best of my knowledge) on Mac OS X.

Requirements

Mac OS X

Xcode (Command Line Tools suffice)

Linux

http://mark.heily.com/libkqueue/

Waiting on directories does not work on Linux at the moment.

Build

To build this just type:

make

If you want to check that everything is working correctly on your machine use:

make test

This requires perl, with modules IPC::Run and Test::More installed.

Usage

Call it like this:

kqwait [-d] [-v] [-h] <file|dir>[ <file|dir>]+

Options

d - enable debug output on stderr
v - print version and exit
h - print help

Operation

The tool prints the file or directory that caused the tool to wake up, and returns 0, if the expected event occured, 1 otherwise.

When waiting on a directory, a + character is prepended if a file was added, a - if a file was deleted.

Use it in a shell script like this:

while ./kqwait text.txt; do
   # do some stuff on write
done

Or watch directories like this:

$ while ./kqwait somedir someotherdir; do true; done
+ somedir/a_file_was_added.txt
- someotherdir/a_file_was_deleted.txt

When watching directories, write events concerning existing files currently won't trigger a return. Only creation and deletion will do that. If you would like to track all events at the same time you can use shell mechanisms to do that:

while ./kqwait dir1/ dir1/*; do
  # something
done

If you want to use the file that caused the return, you can assign the output to a variable:

while file=`./kqwait dir1/`; do
  echo "Event on $file"
done

See a more advanced script, that does some simple dispatch based on file ending under samples/.

Note

There is (at least) one race condition in this code, when waiting for changes on directories. If several events happen on a directory in quick succession, this tool might catch an intermediate snapshot of that chain of events.

Author

Sven Schober sv3sch@gmail.com

License

Copyright (c) 2020, Sven Schober
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:

Redistributions of source code must retain the above copyright notice,
this list of conditions and the following disclaimer.

Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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sschober / kqwait