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Top Forums UNIX for Dummies Questions & Answers How do i lock a ksh shell script? Post 302537255 by gary_w on Thursday 7th of July 2011 01:15:22 PM
Old 07-07-2011
One way...

Maybe someone else will have a more elegant idea, but here's a way that comes to mind.

At the top of your script test for the presence of a file which indicates the script is running. If it is, loop, checking every 5 minutes or whatever until the file does not exist.

If it does not exist, then create it to indicate we are running and remove it at the end.

You could also write a row to a table in the database which logically does the same thing.

Partial code to show the logic:
Code:
#!/bin/ksh

#  Define constants
typeset -r LOCKFILE=/tmp/${0}.lock
typeset -ir LOCKWAITTIME=300   # seconds

# Remove the lock file if the script is interrupted before it ends normally.
trap 'rm $LOCKFILE' 0 2 3 9 15  # 0=normal exit

#  If lockfile exists, wait for it to go away.
if [[ -f $LOCKFILE ]]; then
     print "Waiting...\c"
     while [[ -f $LOCKFILE ]]
     do
       sleep $LOCKWAITTIME
       print ".\c"
     done
fi
# LOCKFILE does not exist so create it.
print "$0: locked by $(logname)" > $LOCKFILE

#script body here

exit 0

This example loops forever, you would most likely want to put a timeout in there I suppose that would exit after maybe 2 or 3 LOCKWAITTIME iterations. Also if more than one process is waiting there could be trouble if they both see the lock file go away at the same time.

Gary

Last edited by gary_w; 07-07-2011 at 02:21 PM..
 

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exit(1)                                                            User Commands                                                           exit(1)

NAME
exit, return, goto - shell built-in functions to enable the execution of the shell to advance beyond its sequence of steps SYNOPSIS
sh exit [n] return [n] csh exit [ ( expr )] goto label ksh *exit [n] *return [n] DESCRIPTION
sh exit will cause the calling shell or shell script to exit with the exit status specified by n. If n is omitted the exit status is that of the last command executed (an EOF will also cause the shell to exit.) return causes a function to exit with the return value specified by n. If n is omitted, the return status is that of the last command exe- cuted. csh exit will cause the calling shell or shell script to exit, either with the value of the status variable or with the value specified by the expression expr. The goto built-in uses a specified label as a search string amongst commands. The shell rewinds its input as much as possible and searches for a line of the form label: possibly preceded by space or tab characters. Execution continues after the indicated line. It is an error to jump to a label that occurs between a while or for built-in command and its corresponding end. ksh exit will cause the calling shell or shell script to exit with the exit status specified by n. The value will be the least significant 8 bits of the specified status. If n is omitted then the exit status is that of the last command executed. When exit occurs when executing a trap, the last command refers to the command that executed before the trap was invoked. An end-of-file will also cause the shell to exit except for a shell which has the ignoreeof option (See set below) turned on. return causes a shell function or '.' script to return to the invoking script with the return status specified by n. The value will be the least significant 8 bits of the specified status. If n is omitted then the return status is that of the last command executed. If return is invoked while not in a function or a '.' script, then it is the same as an exit. On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways: 1. Variable assignment lists preceding the command remain in effect when the command completes. 2. I/O redirections are processed after variable assignments. 3. Errors cause a script that contains them to abort. 4. Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a vari- able assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not performed. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | |Availability |SUNWcsu | +-----------------------------+-----------------------------+ SEE ALSO
break(1), csh(1), ksh(1), sh(1), attributes(5) SunOS 5.10 15 Apr 1994 exit(1)
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