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.IX Title "SHLOCK 1"
.TH SHLOCK 1 2024-04-01 "INN 2.7.2" "InterNetNews Documentation"
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.nh
.SH NAME
shlock \- Create lock files for use in shell scripts
.SH SYNOPSIS
.IX Header "SYNOPSIS"
\&\fBshlock\fR [\fB\-b\fR|\fB\-c\fR|\fB\-u\fR] \fB\-f\fR \fIname\fR \fB\-p\fR \fIpid\fR
.SH DESCRIPTION
.IX Header "DESCRIPTION"
\&\fBshlock\fR tries to create a lock file named \fIname\fR and write
the process ID \fIpid\fR into it.  If the file already exists, \fBshlock\fR
will read the process ID from the file and test to see whether
the process is currently running.  If the process exists, then the file
will not be created.  \fIshlock\fR exits with a zero status if it could
create the lock file, or non-zero if the file refers to a currently
active process.
.PP
A Perl wrapper around \fBshlock\fR can be used via the \f(CW\*(C`INN::Utils::Shlock\*(C'\fR
module.
.SH OPTIONS
.IX Header "OPTIONS"
.IP \fB\-b\fR 4
.IX Item "-b"
Process IDs are normally read and written in ASCII.  If the \fB\-b\fR flag
is used, then they will be written as a binary int.
.IP \fB\-c\fR 4
.IX Item "-c"
If the \fB\-c\fR flag is used, then \fBshlock\fR 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 \fBshlock\fR without the flag would
have succeeded), then the program will exit with a zero status.
.IP "\fB\-f\fR \fIname\fR" 4
.IX Item "-f name"
\&\fIname\fR is the name of the lock file \fBshlock\fR attempts to create.
If the file already exists, it will read the process ID from the file
and exit with a non-zero status if this process is currently active.
.IP "\fB\-p\fR \fIpid\fR" 4
.IX Item "-p pid"
\&\fIpid\fR is the process ID to write into the file \fIname\fR.
.IP \fB\-u\fR 4
.IX Item "-u"
For compatibility with other systems, the \fB\-u\fR flag is accepted
as a synonym for \fB\-b\fR since binary locks are used by many UUCP packages.
.SH EXAMPLES
.IX Header "EXAMPLES"
The following example shows how \fBshlock\fR would be used within
a shell script:
.PP
.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
.SH HISTORY
.IX Header "HISTORY"
Written by Rich $alz <rsalz@uunet.uu.net> for InterNetNews after
a description of HDB UUCP locking given by Peter Honeyman, and
improved by Berend Reitsma to solve a race condition.
Converted to POD by Julien Elie.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
INN::Utils::Shlock(3pm).