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The restricted shell is a Unix shell that restricts some of the capabilities available to an interactive user session, or to a shell script, running within it.It is intended to provide an additional layer of security, but is insufficient to allow execution of entirely untrusted software.
When a command is terminated by a signal whose number is N, a shell sets the variable $? to a value greater than 128. Most shells use 128+N, while ksh93 uses 256+N. If a command is not found, the shell should return a status of 127. If a command is found but is not executable, the return status should be 126. [2]
On DOS, OS/2, and Windows operating systems, the %PATH% variable is specified as a list of one or more directory names separated by semicolon (;) characters. [5]The Windows system directory (typically C:\WINDOWS\system32) is typically the first directory in the path, followed by many (but not all) of the directories for installed software packages.
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.
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.
Users can, and often do, augment them in the profile script for the command shell they are using. In Microsoft Windows, each environment variable's default value is stored in the Windows Registry or set in the AUTOEXEC.BAT file. On Unix, a setuid program is given an environment chosen by its caller, but it runs with different authority from its ...
A shell that can determine ahead of invocation that there are missing mandatory values, can assist the interactive user by prompting for those values instead of letting the command fail. Having the shell prompt for missing values will allow the author of a script, command or function to mark a parameter as mandatory instead of creating script ...
The command-line environment may not provide graphical enhancements such as different fonts or extended edit windows found in a GUI. It may be difficult for a new user to become familiar with all the commands and options available, compared with the icons and drop-down menus of a graphical user interface, without reference to manuals.