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The test command in Unix evaluates the expression parameter. In most recent shell implementations, it is a shell builtin, even though the external version still exists.In the second form of the command, the [ ] (brackets) must be surrounded by blank spaces (this is because [is a program and POSIX compatible shells require a space between the program name and its arguments).
A shell script is a computer program designed to be run by a Unix shell, a command-line interpreter. [1] The various dialects of shell scripts are considered to be command languages . Typical operations performed by shell scripts include file manipulation, program execution, and printing text.
In MS-DOS, a batch file can be started from the command-line interface by typing its name, followed by any required parameters and pressing the ↵ Enter key. When DOS loads, the file AUTOEXEC.BAT, when present, is automatically executed, so any commands that need to be run to set up the DOS environment may be placed in this file.
In Linux, if the script was executed by a regular user, the shell would attempt to execute the command rm -rf / as a regular user, and the command would fail. However, if the script was executed by the root user, then the command would likely succeed and the filesystem would be erased. It is recommended to use sudo on a per-command basis instead.
In the lower right we can see a terminal emulator running a Unix shell, in which the user can type commands as if they were sitting at a terminal. In computing, a shell is a computer program that exposes an operating system's services to a human user or other programs.
But {{{1|}}} will evaluate to the empty string (a false value) because the vertical bar or pipe character, "|", immediately following the parameter name specifies a default value (here an empty string because there is nothing between the pipe and the first closing curly brace) as a "fallback" value to be used if the parameter is undefined.
tcsh and sh shell windows on a Mac OS X Leopard [1] desktop. 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 ...
If /bin/sh is a POSIX-compatible shell, then bar and baz are presented to the script as the positional parameter array "$@", and individually as parameters "$1" and "$2" respectively. Because the initial # is the character used to introduce comments in the POSIX shell language (and in the languages understood by many other interpreters), the ...