12-27-2018
Oh okay I was confused then. So the locations /usr/bin ect are where programs like cp or rm are located. In other words, its similar to importing a library in Python or Java. Once I specify those locations if I call one of the programs it will look there and see if that program exists and if it does it will run the program. I am only wondering because I am attempting to understand what this script is doing. Some parts of it are obvious, other parts are not. However, I find myself wondering why some programs like echo can be called without first specifying a PATH.
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PIDOF(8) Linux System Administrator's Manual PIDOF(8)
NAME
pidof -- find the process ID of a running program.
SYNOPSIS
pidof [-s] [-c] [-n] [-x] [-o omitpid[,omitpid..]] [-o omitpid[,omitpid..]..] program [program..]
DESCRIPTION
Pidof finds the process id's (pids) of the named programs. It prints those id's on the standard output. This program is on some systems
used in run-level change scripts, especially when the system has a System-V like rc structure. In that case these scripts are located in
/etc/rc?.d, where ? is the runlevel. If the system has a start-stop-daemon (8) program that should be used instead.
OPTIONS
-s Single shot - this instructs the program to only return one pid.
-c Only return process ids that are running with the same root directory. This option is ignored for non-root users, as they will be
unable to check the current root directory of processes they do not own.
-n Avoid stat(2) system function call on all binaries which are located on network based file systems like NFS. Instead of using this
option the the variable PIDOF_NETFS may be set and exported.
-x Scripts too - this causes the program to also return process id's of shells running the named scripts.
-o omitpid
Tells pidof to omit processes with that process id. The special pid %PPID can be used to name the parent process of the pidof pro-
gram, in other words the calling shell or shell script.
EXIT STATUS
0 At least one program was found with the requested name.
1 No program was found with the requested name.
NOTES
pidof is actually the same program as killall5; the program behaves according to the name under which it is called.
When pidof is invoked with a full pathname to the program it should find the pid of, it is reasonably safe. Otherwise it is possible that
it returns pids of running programs that happen to have the same name as the program you're after but are actually other programs. Note
that that the executable name of running processes is calculated with readlink(2), so symbolic links to executables will also match.
SEE ALSO
shutdown(8), init(8), halt(8), reboot(8), killall5(8)
AUTHOR
Miquel van Smoorenburg, miquels@cistron.nl
01 Sep 1998 PIDOF(8)