flock

lock files for use by shell scripts

Contributed by

David J. Fiander

Obtained from

I wrote it

Restrictions

SCO owns it (because I wrote it. Ask John MacMillan)

Description

This locks files using fcntl file locking. If the lock is successfully acquired, then the pid of a process holding the lock is printed on stdout, otherwise and error message is printed, and the exit status is the value of errno. "flock -r" gives a read or shared lock, "flock -w", or just "flock", gives a write, or exclusive, lock.

Productivity

great for locking mailboxes while you edit them with vi ;->

Safety

Wrote it. It's only 2 screens long.

Work Planned

None

Documentation

None

Verification

say "flock ", see a pid. try again. It should fail. Kill the given pid, and try the lock again. NOTE: If compiled on XENIX, write locks are pretty useless, since the only locking implemented is mandatory.