Bash script if statement returning incorrect result while bash -x works

Question

I have a simple bash script that checks if a program is running and actions accordingly.

#!/bin/bash

check_running=$(pgrep -x redshift)

if [[ -n "$check_running" ]]; then
    echo "1"
    else
        echo "0"
fi

If I execute the script normally (./script) then it will always return 1. But if I use "bash -x script" then it returns the correct outcome

❯ bash -x redshift
++ pgrep -x redshift
+ check_running=
+ [[ -n '' ]]
+ echo 0
0

I have a similar script checking if openvpn is running and it returns the correct value via regular execution.

Here it is in full:

~/.config/polybar/scripts
❯ pgrep -x redshift

~/.config/polybar/scripts
❯ ./redshift       
1

~/.config/polybar/scripts
❯ bash -x redshift 
++ pgrep -x redshift
+ check_running=
+ [[ -n '' ]]
+ echo 0
0

What am I doing wrong?

Answer 1

When you run ./redscript, pgrep -x redscript will match that script's process, so check_running will have a PID. You can put a set -x in the script, or use #! /bin/bash -x as the shebang, to verify this.