PATH (variable)
PATH is an environment variable on Unix-like operating systems, DOS, OS/2, and Microsoft Windows, specifying a set of directories where executable programs are located. In general, each executing process or user session has its own PATH setting.
History
Multics originated the idea of a search path. The early Unix shell only looked for program names in /bin, but by Version 3 Unix the directory was too large and /usr/bin, and a search path, became part of the operating system.
Unix and Unix-like
On POSIX and Unix-like operating systems, the $PATH variable is specified as a list of one or more directory names separated by colon (:) characters.
The /bin, /usr/bin, and /usr/local/bin directories are typically included in most users' $PATH setting (although this varies from implementation to implementation). The superuser also typically has /sbin and /usr/sbin entries for easily executing system administration commands. The current directory (.) is sometimes included by users as well, allowing programs residing in the current working directory to be executed directly. Superuser (root) accounts as a rule do not include it in $PATH, however, in order to prevent the accidental execution of scripts residing in the current directory, such as may be placed there by a malicious tarbomb. In that case, executing such a program requires specifying an absolute (/home/userjoe/bin/script.sh) or relative path (./script.sh) on the command line.
