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.


     -b   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

     -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.

     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}`

     Written by Rich $alz <> after a description of HDB UUCP
     locking given by Peter Honeyman.  This is revision 1.9, dated 1996/10/29.

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