Question

I have a script that I only want to be running one time. If the script gets called a second time I’m having it check to see if a lockfile exists. If the lockfile exists then I want to see if the process is actually running.

I’ve been messing around with pgrep but am not getting the expected results:

#!/bin/bash
COUNT=$(pgrep $(basename $0) | wc -l)
PSTREE=$(pgrep $(basename $0) ; pstree -p $$)
echo "###"
echo $COUNT
echo $PSTREE
echo "###"
echo "$(basename $0) :" `pgrep -d, $(basename $0)`
echo sleeping.....
sleep 10

The results I’m getting are:

$ ./test.sh  
###
2
2581 2587 test.sh(2581)---test.sh(2587)---pstree(2591)
###
test.sh : 2581
sleeping.....

I don’t understand why I’m getting a “2” when only one process is actually running.

Any ideas? I’m sure it’s the way I’m calling it. I’ve tried a number of different combinations and can’t quite seem to figure it out.

SOLUTION:

What I ended up doing was doing this (portion of my script):

function check_lockfile {
    # Check for previous lockfiles

    if [ -e $LOCKFILE ] 
    then
        echo "Lockfile $LOCKFILE already exists.  Checking to see if process is actually running...." >> $LOGFILE 2>&1
        # is it running?
        if [ $(ps -elf | grep $(cat $LOCKFILE) | grep $(basename $0) | wc -l) -gt 0 ]
        then
            abort "ERROR! - Process is already running at PID: $(cat $LOCKFILE).  Exitting..."
        else
            echo "Process is not running.  Removing $LOCKFILE" >> $LOGFILE 2>&1
            rm -f $LOCKFILE
        fi
    else
        echo "Lockfile $LOCKFILE does not exist." >> $LOGFILE 2>&1
    fi
}

function create_lockfile {
    # Check for previous lockfile
    check_lockfile

    #Create lockfile with the contents of the PID
    echo "Creating lockfile with PID:" $$ >> $LOGFILE 2>&1
    echo -n $$ > $LOCKFILE
    echo "" >> $LOGFILE 2>&1
}

# Acquire lock file
create_lockfile >> $LOGFILE 2>&1 \
|| echo "ERROR! - Failed to acquire lock!"

Answer 1

The argument for pgrep is an extended regular expression pattern.
In you case the command pgrep $(basename $0) will evaluate to pgrep test.sh which will match match any process that has test followed by any character and lastly followed by sh. So it wil match btest8sh, atest_shell etc.

You should create a lock file. If the lock file exists program should exit.

lock=$(basename $0).lock
if [ -e $lock ] 
then 
    echo Process is already running with PID=`cat $lock`
    exit
else
    echo $$ > $lock
fi