SHELL

bash get current process id

$! is the PID of the last backgrounded process.
kill -0 $PID checks whether it's still running.
$$ is the PID of the current shell.

find the process ID of a running process bash

# Procedure to find process by name on Linux

# Open the terminal application.

# Type the pidof command as follows to find PID for firefox process:
$ pidof firefox

# Or use the ps command along with grep command as follows:
$ ps aux | grep -i <search term>

# To look up or single processes based on name use the following syntax:
$ pgrep firefox