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Full Discussion: How to lock a file in unix?
Top Forums UNIX for Dummies Questions & Answers How to lock a file in unix? Post 2631 by tammy_schmuki on Friday 25th of May 2001 08:30:37 AM
Old 05-25-2001
Lightbulb

We wish to keep a sequence number in a file. When someone wants to get the next sequence number we need to lock the file, get the next number and increment it by one. How do you do that?

I know how to get the number and increment it but how do I lock the file and test that it is locked or not locked.
x=`cat filewithseq`
x=x+1
echo $x > filewithseq
Someone must be doing this already. I know that printer job numbers work in a similar way.
 

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WLOCK(1)						       System Administration							  WLOCK(1)

NAME
wlock - Tests or sets a file with POSIX-fcntl() write-locks SYNOPSIS
wlock [ -s [-a seconds ]] [ -t] [ -v] [ -b begin ] [ -l length ] file or wlock [ -s ] [ -v] [ -b begin ] [ -l length ] file program [ arguments ] DESCRIPTION
This program sets or tests advisory locks conforming to POSIX fcntl() call. You may specify optionaly a program to start it within the lock context. OPTIONS
These options are accepted. If a program is provided as argument wlock will start it. -s Sets the lock. -t Test the lock (default). -v Verbose output. -b begin The lock starts at byte #begin. -l length The lock will be length bytes long. -a seconds The lock is active for seconds (default=86400). RETURN VALUES
0 In test mode this means that the file is locked. In set mode it indicates the succesful creation of the lockfile 1 The file is not locked. Only available in testmode. 2 Some error has occurred. AUTHOR
wlock has been written by Ulli Horlacher (framstag@belwue.de>. SEE ALSO
sendfile(1). 19 March 1998 WLOCK(1)
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