SHLOCK man page on 4.4BSD

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SHLOCK(1)							     SHLOCK(1)

       shlock - create lock files for use in shell scripts

       shlock -p pid -f name [ -b ] [ -u ] [ -c ]

       Shlock  tries to create a lock file named name and write the process ID
       pid into it.  If the file already exists, shlock will read the  process
       ID  from	 the file and test to see if the process is currently running.
       If the process exists, then the file will not be created.

       Shlock exits with a zero status if it was able to create the lock file,
       or non-zero if the file refers to currently-active process.

       Process IDs are normally read and written in ASCII.  If the ``-b'' flag
       is used, then they will be written as a binary int.  For	 compatibility
       with other systems, the ``-u'' flag is accepted as a synonym for ``-b''
       since binary locks are used by many UUCP packages.

       The following example shows how shlock would be	used  within  a	 shell
	      trap 'rm -f ${LOCK} ; exit 1' 1 2 3 15
	      if shlock -p $$ -f ${LOCK} ; then
		  # Do appropriate work
		  echo Locked by `cat ${LOCK}`

       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  be  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 sta‐

       Written by Rich $alz <> after a  description  of  HDB
       UUCP  locking  given  by	 Peter	Honeyman.  This is revision 1.7, dated


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