what's the difference of 'which' and' whence'?

[常有慈悲心]

i find whence is a built-in shell command,
is it not product a new subprocess ,
while which produce a new subprocess ,because
'which' is a os command?

[Sridhar Bhaskarla · Accepted solution]

Hi,

Yes. 'Whence' is built-in command to Korn Shell and can recognize aliases in addition. "which" is a command and runs as a seperate process.

-Sri

[Franky_1]

Hi,

whence is a shell built-in and is normally set as alias for type (whence -v)

which is a process (/usr/bin/which)

Because there's no manual for whence you can find some hints looking for man sh-posix
and then searching for whence

Regards

Franky

[Muthukumar_5]

whence is a built-in binary with korn shell. It is used to search a shell function name, alias name, or keyword

which is a system binary used to locate system's routines or binaries location by searching PATH locations.

Both of the binaries are using to search shell environment variable PATH.

By default, built-in binaries associated with shells will not fork a sub-process. But which is not related to shell so it will fork a new process.

[Geoff Wild]

From man:

whence - locate a command and describe its type
Without -v, whence writes on standard output an absolute pathname, if any, corresponding to name based on the complete search order that the shell uses. If name not found, then no output is produced.

If -v is specified, the output will also contain information that indicates how the given name would be interpretted by the shell in the current execution environment.

whence (AT&T Labs Research) 1999-07-07
author
David Korn


which - locate a program file including aliases and paths For each name given, which searches for the file that would be executed if name were given as a command, and displays the absolute path of that file. Each argument is expanded if it is aliased, and searched for along the user's path. Both aliases and path are determined by sourcing (executing) the user's .cshrc file.

which was developed by the University of California, Berkeley.


Rgds...Geoff