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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).
In a Unix shell, the full stop called the dot command (.) is a command that evaluates commands in a computer file in the current execution context. [1] In the C shell, a similar functionality is provided as the source command, [2] and this name is seen in "extended" POSIX shells as well.
The lack of an interpreter directive, but support for shell scripts, is apparent in the documentation from Version 7 Unix in 1979, [28] which describes instead a facility of the Bourne shell where files with execute permission would be handled specially by the shell, which would (sometimes depending on initial characters in the script, such as ...
Some Unix shells, like the POSIX standard sh shell, use an ampersand to execute a process in the background and to duplicate file descriptors. In Bash, the ampersand can separate words, control the command history, duplicate file descriptors, perform logical operations, control jobs, and participate in regular expressions. [41]
If a script is invoked as an argument to the interpreting shell, it will be executed regardless of whether the user holds the execute permission for that script. Although Windows also specifies an execute permission, none of the Windows-specific shells block script execution if the permission has not been granted.
Editing a FreeBSD shell script for configuring ipfirewall. 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 ...
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 ...
Operator precedence is also borrowed from C, but with different operator associativity rules to resolve the ambiguity of what comes first in a sequence of equal precedence operators. In C, the associativity is left-to-right for most operators; in C shell, it is right-to-left.