Pgrep

codice_1 is a command-line utility initially written for use with the Solaris 7 operating system by Mike Shapiro. It has since been available in illumos and reimplemented for the Linux and BSDs (DragonFly BSD, FreeBSD, NetBSD, and OpenBSD). It searches for all the named processes that can be specified as extended regular expression patterns, and—by default—returns their process ID. Alternatives include codice_2 (finds process ID given a program name) and codice_3.
Example usage.
The default behaviour of codice_1 (returning the process identifier of the named tasks) simplifies an otherwise complex task and is invoked with:
$ pgrep 'bash'
Which is roughly equivalent to:
$ ps ax | awk '{sub(/.*\//, "", $5)} $5 ~ /bash/ {print $1}'
Additional functionality of codice_1 is listing the process name as well as the PID (-l Lists the process name as well as the process ID) of all processes belonging to the group codice_6 (-G Only match processes whose real group ID is listed. Either the numerical or symbolical value may be used):
$ pgrep -l -G alice
showing all processes that do not belong to the user codice_7 (-u euid Only match processes whose effective user ID is listed. Either the numerical or symbolical value may be used) by inverting the matching (-v Negates the matching):
$ pgrep -v -u root
and only matching the most recently started process (-n Select only the newest (most recently started) of the matching processes):
$ pgrep -n # The most recent process started
$ pgrep -n -u alice emacs # The most recent `emacs` process started by user `alice`