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.\" ========================================================================
.\"
.IX Title "SHLOCK 1"
.TH SHLOCK 1 "2015-09-12" "INN 2.6.4" "InterNetNews Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.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 \s-1ID\s0 \fIpid\fR into it.  If the file already exists, \fBshlock\fR
will read the process \s-1ID\s0 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 \s-1ASCII.\s0  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 \s-1ID\s0 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 \s-1ID\s0 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 \s-1UUCP\s0 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 ${LOCK}\`"
\&    fi
.Ve
.SH "HISTORY"
.IX Header "HISTORY"
Written by Rich \f(CW$alz\fR <rsalz@uunet.uu.net> for InterNetNews after
a description of \s-1HDB UUCP\s0 locking given by Peter Honeyman, and
improved by Berend Reitsma to solve a race condition.
Converted to \s-1POD\s0 by Julien Elie.
.PP
\&\f(CW$Id:\fR shlock.pod 9303 2011\-08\-04 22:09:57Z iulius $
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBINN::Utils::Shlock\fR\|(3pm).