Determining if process is running using pgrep - bash

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

Answer 2

You are already opening a lock file. Use it to make your life easier.
Write the process id to the lock file. When you see the lock file exists, read it to see what process id it is supposedly locking, and check to see if that process is still running.
Then in version 2, you can also write program name, program arguments, program start time, etc. to guard against the case where a new process starts with the same process id.

Answer 3

Put this near the top of your script...
pid=$$
script=$(basename $0)
guard="/tmp/$script-$(id -nu).pid"
if test -f $guard ; then
echo >&2 "ERROR: Script already runs... own PID=$pid"
ps auxw | grep $script | grep -v grep >&2
exit 1
fi
trap "rm -f $guard" EXIT
echo $pid >$guard
And yes, there IS a small window for a race condition between the test and echo commands, which can be fixed by appending to the guard file, and then checking that the first line is indeed our own PID. Also, the diagnostic output in the if can be commented out in a production version.