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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 ...
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.
The interpreter would execute one of a number of predefined commands, one of which would be to run a user program. Common commands would log the user on and off the system, allocate, free, and manipulate devices and files, and query various pieces of information about the system or a user process. [7]
After authentication, and if the configuration file permits the user access, the system invokes the requested command. sudo retains the user's invocation rights through a grace period (typically 5 minutes) per pseudo terminal, allowing the user to execute several successive commands as the requested user without having to provide a password again.
JP Software command-line processors provide user-configurable colorization of file and directory names in directory listings based on their file extension and/or attributes through an optionally defined %COLORDIR% environment variable. For the Unix/Linux shells, this is a feature of the ls command and the terminal.
The C shell is a command processor which is typically run in a text window, allowing the user to type and execute commands. The C shell can also read commands from a file, called a script . Like all Unix shells, it supports filename wildcarding , piping , here documents , command substitution , variables and control structures for condition ...
The r, w, and x specify the read, write, and execute access respectively. The first character of the ls -l display denotes the object type; a hyphen represents a plain file. The script findPhoneNumbers.sh can be read, written to, and executed by the user dgerman; read and executed by members of the staff group; and only read by any other users.
A common value is /bin/sh, but some systems such as Solaris have the POSIX-compatible shell at /usr/xpg4/bin/sh. [13] In many Linux systems, /bin/sh is a hard or symbolic link to /bin/bash, the Bourne Again shell (BASH). Using bash-specific syntax while maintaining a shebang pointing to sh is also not portable. [14]