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Path hashing speeds up the C shell's search for executable files. Rather than performing a filesystem call in each path directory, one at a time, until it either finds the file or runs out of possibilities, the C shell consults an internal hash table built by scanning the path directories.
When the user gives a command, the shell searches for the command in the path specified in the PATH environmental variable and stores the location in the hash. This command can be used to search for the command given. The command is built into the shell. C shell implements this command in a different way.
Previously (and in fact still) the shell did much of this job; it automatically executed itself on a text file with executable mode when the text file's name was typed as a command. Putting the facility into the system gives the following benefits. 1) It makes shell scripts more like real executable files, because they can be the subject of 'exec.'
The C shell (csh or the improved version, tcsh) is a Unix shell created by Bill Joy while he was a graduate student at University of California, Berkeley in the late 1970s. It has been widely distributed, beginning with the 2BSD release of the Berkeley Software Distribution (BSD) which Joy first distributed in 1978.
The C shell also introduced many features for interactive work, including the history and editing mechanisms, aliases, directory stacks, tilde notation, cdpath, job control and path hashing. On many systems, csh may be a symbolic link or hard link to TENEX C shell (tcsh), an improved version of Joy's original version. Although the interactive ...
(FreeBSD 14 changed the default root shell to sh to match the default user shell [5] whereas OpenBSD uses the Korn shell ksh for both root and regular users. [6]) tcsh added filename and command completion and command line editing concepts borrowed from the TENEX operating system, which is the source of the “t”. [7]
It does this by searching for an executable or script in the directories listed in the environment variable PATH. The which command is part of most Unix-like computers. It is also part of the C Shell. [6] A which command first appeared in 3BSD. [7] Carlo Wood developed the GNU implementation used in most Linux-based operating systems. [8]
The popd command removes (or 'pops', in the stack analogy) the current path entry from the stack and returns to the path at the top of the stack as the new working directory. [ 4 ] [ 5 ] The first Unix shell to implement a directory stack was Bill Joy's C shell .