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On Unix-like platforms, usage messages usually follow the same common pattern: They often begin with "Usage:" , the command, followed by a list of arguments . To indicate optional arguments, square brackets are commonly used, and can also be used to group parameters that must be specified together.
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.
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.
Kernel support for interpreter directives spread to other versions of Unix, and one modern implementation can be seen in the Linux kernel source in fs/binfmt_script.c. [31] This mechanism allows scripts to be used in virtually any context normal compiled programs can be, including as full system programs, and even as interpreters of other scripts.
For example, the diff command operates on two files at a time. The -n option to xargs specifies how many arguments at a time to supply to the given command. The command will be invoked repeatedly until all input is exhausted. Note that on the last invocation one might get fewer than the desired number of arguments if there is insufficient input.
PHP uses argc as a count of arguments and argv as an array containing the values of the arguments. [ 4 ] [ 5 ] To create an array from command-line arguments in the -foo:bar format, the following might be used:
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 Unix shells .
The alias concept from csh was imported into Bourne Again Shell (bash) and the Korn shell (ksh). With shells that support both functions and aliases but no parameterized inline shell scripts, the use of functions wherever possible is recommended. Cases where aliases are necessary include situations where chained aliases are required (bash and ksh).