Linux Shell Scripting Cookbook - Third Edition

Finding the process ID from the given command names

Suppose several instances of a command are being executed. In such a scenario, we need the PID of each process. Both the ps and pgrep command return this information:

    $ ps -C COMMAND_NAME

Alternatively, the following is returned:

    $ ps -C COMMAND_NAME -o pid=

When = is appended to pid, it removes the header PID from the output of ps. To remove headers from a column, append = to the parameter.

This command lists the process IDs of Bash processes:

    $ ps -C bash -o pid=
     1255
     1680

The pgrep command also returns a list of process IDs for a command:

    $ pgrep bash
    1255
    1680

pgrep requires only a portion of the command name as its input argument to extract a Bash command; pgrep ash ...