add_line appends a line to a file. remove_line removes the first occurrence of such a line, if any; the return status indicates whether a line was removed. Fairly useless, except that these programs flock() the file for exclusive access, so the updates are atomic. You can use them in shell scripts to keep track of things (eg add_line when you log in, remove_line when you log out, then you have a list of all machines currently logged into) or for mutual exclusion (the README gives an example of building a semaphore).
All the files are in the public domain. This means there are no copyright restrictions, you may do what you wish with them. Of course, giving credit would be appreciated (but not required). They are offered as-is with no warranty whatsoever.
Written by Ed Avis ed@membled.com.