mjhjmtu

In my box, the code /bin/ps -aux | /bin/grep -c "blynk"returns a 1 because blynk server is not running.

However, when the same code is ran in a bash file, it returns 4. How does that happen?

#!/bin/sh
stat=`/bin/ps -aux | /bin/grep -c "blynk"`
if [ $stat -lt "2" ]; then
 echo not running
else 
 echo running
 date
fi

You get a higher number from the grep because there are more programs running that match the pattern.

If you look at the output of grep (without the -c), you'll see which lines in the output of ps match. E.g. if I make a script like this, I get three:

$ cat check_blynk.sh
#!/bin/bash
foo=$(/bin/ps a | /bin/grep "blynk")
echo "$foo"

$ bash check_blynk.sh
28874 pts/11 S+ 0:00 bash check_blynk.sh
28875 pts/11 S+ 0:00 bash check_blynk.sh
28877 pts/11 S+ 0:00 /bin/grep blynk

That's one for the grep, since the pattern it uses matches itself, one for script that just so happens to contain the same word in its name, and another for the fact that the ps | grep is running in a subshell, i.e. another copy of the shell. (I'm not sure what the fourth one would be.)

You might want to use something like pgrep -c blynk instead, assuming blynk is the name of program file. pgrep by default checks the actual file name of the running program, instead of the whole command line. (With -f it checks the command line, but the you'll match the Bash script again)

You have to prevent grep from finding itself. An easy way to do that is this:

/bin/ps -aux | /bin/grep -c "[b]lynk"

That way grep searches for blynk without having it in its command line. Or you prevent grep from running at the same time:

/bin/ps -aux >ps.txt
/bin/grep -c "[b]lynk" ps.txt

Of course, it makes sense to not grep command lines at all because you would also find editors which were opened with a file README.blynk.

Thus it is better to use pgrep or modify the ps output, limit it to command names or command paths.

A bash function to check if a process of a command is running, defunct (zombie, dead) excluded:

_isRunning() 
 ps -o comm= -C "$1" 2>/dev/null 

Note: ps reports defunct processes too, so, grep -x is used

Example usages:

if _isRunning blynk; then
 echo not running
else 
 echo running
 date
fi