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Title "SHLOCK 1" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
shlock - Create lock files for use in shell scripts Header "SYNOPSIS" \fBshlock [-b|-c|-u] -f name -p pid Header "DESCRIPTION" \fBshlock tries to create a lock file named name and write the process \s-1ID\s0 pid into it. If the file already exists, shlock will read the process \s-1ID\s0 from the file and test to see whether the process is currently running. If the process exists, then the file will not be created. shlock exits with a zero status if it could create the lock file, or non-zero if the file refers to a currently active process.

A Perl wrapper around shlock can be used via the \*(C`INN::Utils::Shlock\*(C' module.

Header "OPTIONS" Item "-b" Process IDs are normally read and written in \s-1ASCII.\s0 If the -b flag is used, then they will be written as a binary int. Item "-c" If the -c flag is used, then shlock will not create a lock file, but will instead use the file to see if the lock is held by another program. If the lock is valid, the program will exit with a non-zero status; if the lock is not valid (i.e. invoking shlock without the flag would have succeeded), then the program will exit with a zero status. Item "-f name" \fIname is the name of the lock file shlock attempts to create. If the file already exists, it will read the process \s-1ID\s0 from the file and exit with a non-zero status if this process is currently active. Item "-p pid" \fIpid is the process \s-1ID\s0 to write into the file name. Item "-u" For compatibility with other systems, the -u flag is accepted as a synonym for -b since binary locks are used by many \s-1UUCP\s0 packages. Header "EXAMPLES" The following example shows how shlock would be used within a shell script:

.Vb 7 LOCK=<pathrun in inn.conf>/LOCK.send trap \*(Aqrm -f ${LOCK} ; exit 1\*(Aq 1 2 3 15 if shlock -p $$ -f ${LOCK} ; then # Do appropriate work. else echo "Locked by \`cat ${LOCK}\`" fi .Ve

Header "HISTORY" Written by Rich $alz <rsalz@uunet.uu.net> for InterNetNews after a description of \s-1HDB UUCP\s0 locking given by Peter Honeyman, and improved by Berend Reitsma to solve a race condition. Converted to \s-1POD\s0 by Julien Elie.

\f(CW$Id: shlock.pod 9303 2011-08-04 22:09:57Z iulius $

Header "SEE ALSO" \fBINN::Utils::Shlock\|(3pm).