Simple bash script count running processes by name - bash

Question

i'm working on a small bash script which counts how often a script with a certain name is running.
ps -ef | grep -v grep | grep scrape_data.php | wc -l
is the code i use, via ssh it outputs the number of times scrape_data.php is running. Currently the output is 3 for example. So this works fine.
Now I'm trying to make a little script which does something when the count is smaller than 1.
#!/bin/sh
if [ ps -ef | grep -v grep | grep scrape_data.php | wc -l ] -lt 1; then
exit 0
#HERE PUT CODE TO START NEW PROCESS
else
exit 0
fi
The script above is what I have so far, but it does not work. I'm getting this error:
[root#s1 crons]# ./check_data.sh
./check_data.sh: line 4: [: missing `]'
wc: invalid option -- e
What am I doing wrong in the if statement?

Answer 1

Your test syntax is not correct, the lt should be within the test bracket:
if [ $(ps -ef | grep -v grep | grep scrape_data.php | wc -l) -lt 1 ]; then
echo launch
else
echo no launch
exit 0
fi
or you can test the return value of pgrep:
pgrep scrape_data.php &> /dev/null
if [ $? ]; then
echo no launch
fi

Answer 2

if you're using Bash then drop [ and -lt and use (( for arithmetic comparisons.
ps provides the -C switch, which accepts the process name to look for.
grep -v trickery are just hacks.
#!/usr/bin/env bash
proc="scrape_data.php"
limit=1
numproc="$(ps hf -opid,cmd -C "$proc" | awk '$2 !~ /^[|\\]/ { ++n } END { print n }')"
if (( numproc < limit ))
then
# code when less than 'limit' processes run
printf "running processes: '%d' less than limit: '%d'.\n" "$numproc" "$limit"
else
# code when more than 'limit' processes run
printf "running processes: '%d' more than limit: '%d'.\n" "$numproc" "$limit"
fi

Answer 3

Counting the lines is not needed. Just check the return value of grep:
if ! ps -ef | grep -q '[s]crape_data.php' ; then
...
fi
The [s] trick avoids the grep -v grep.

Answer 4

While the top-voted answer does in fact work, I have a solution that I used for my scraper that worked for me.
<?php
/**
* Go_Get.php
* -----------------------------------------
* #author Thomas Kroll
* #copyright Creative Commons share alike.
*
* #synopsis:
* This is the main script that calls the grabber.php
* script that actually handles the scraping of
* the RSI website for potential members
*
* #usage: php go_get.php
**/
ini_set('max_execution_time', 300); //300 seconds = 5 minutes
// script execution timing
$start = microtime(true);
// how many scrapers to run
$iter = 100;
/**
* workload.txt -- next record to start with
* workload-end.txt -- where to stop at/after
**/
$s=(float)file_get_contents('./workload.txt');
$e=(float)file_get_contents('./workload-end.txt');
// if $s >= $e exit script otherwise continue
echo ($s>=$e)?exit("Work is done...exiting".PHP_EOL):("Work is not yet done...continuing".PHP_EOL);
echo ("Starting Grabbers: ".PHP_EOL);
$j=0; //gotta start somewhere LOL
while($j<$iter)
{
$j++;
echo ($j %20!= 0?$j." ":$j.PHP_EOL);
// start actual scraping script--output to null
// each 'grabber' goes and gets 36 iterations (0-9/a-z)
exec('bash -c "exec nohup setsid php grabber.php '.$s.' > /dev/null 2>&1 &"');
// increment the workload counter by 36 characters
$s+=36;
}
echo PHP_EOL;
$end = microtime(true);
$total = $end - $start;
print "Script Execution Time: ".$total.PHP_EOL;
file_put_contents('./workload.txt',$s);
// don't exit script just yet...
echo "Waiting for processes to stop...";
// get number of php scrapers running
exec ("pgrep 'php'",$pids);
echo "Current number of processes:".PHP_EOL;
// loop while num of pids is greater than 10
// if less than 10, go ahead and respawn self
// and then exit.
while(count($pids)>10)
{
sleep(2);
unset($pids);
$pids=array();
exec("pgrep 'php'",$pids);
echo (count($pids) %15 !=0 ?count($pids)." ":count($pids).PHP_EOL);
}
//execute self before exiting
exec('bash -c "exec nohup setsid php go_get.php >/dev/null 2>&1 &"');
exit();
?>
Now while this seems like a bit of overkill, I was already using PHP to scrape the data (like your php script in the OP), so why not use PHP as the control script?
Basically, you would call the script like this:
php go_get.php
and then just wait for the first iteration of the script to finish. After that, it runs in the background, which you can see if you use your pid counting from the command line, or a similar tool like htop.
It's not glamorous, but it works. :)