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In computing, command substitution is a facility that allows a command to be run and its output to be pasted back on the command line as arguments to another command. . Command substitution first appeared in the Bourne shell, [1] introduced with Version 7 Unix in 1979, and has remained a characteristic of all later Uni
The shells bash, zsh and PowerShell offer this as a specific feature. [69] [70] Shells which do not offer this as a specific feature may still be able to turn off echoing through some other means. Shells executing on a Unix/Linux operating system can use the stty external command to switch off/on echoing of input characters. [71]
The Bourne shell (sh) is a shell command-line interpreter for computer operating systems.It first appeared on Version 7 Unix, as its default shell. Unix-like systems continue to have /bin/sh—which will be the Bourne shell, or a symbolic link or hard link to a compatible shell—even when other shells are used by most users.
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] On FreeBSD, the which utility was originally written in Perl by Wolfram Schneider.
A Unix shell is a command-line interpreter or shell that provides a command line user interface for Unix-like operating systems. The shell is both an interactive command language and a scripting language , and is used by the operating system to control the execution of the system using shell scripts .
getopt is a system dependent function, and its behavior depends on the implementation in the C library. Some custom implementations like gnulib are available, however. [6]The conventional (POSIX and BSD) handling is that the options end when the first non-option argument is encountered, and that getopt would return -1 to signal that.
Note spaces around argument d* are required. Unix-like systems: ls -lS D* ls -S -l D* display in long format files and directories whose names begin with D (but not d), sorted by size (largest first). Note spaces are required around all arguments and options, but some can be run together, e.g. -lS is the same as -l -S. Data General RDOS CLI
While Bash was developed for UNIX and UNIX-like operating systems, such as GNU/Linux, it is also available on Android, macOS, Windows, and numerous other current and historical operating systems. [12] "Although there have been attempts to create specialized shells, the Bourne shell derivatives continue to be the primary shells in use."