A shell script is a computer program designed to be run by a Unix shell, a command-line interpreter. The various dialects of shell scripts are considered to be scripting languages. Typical operations performed by shell scripts include file manipulation, program execution, and printing text. A script which sets up the environment, runs the program, and does any necessary cleanup or logging, is called a wrapper. The term is also used more generally to mean the automated mode of running an operating system shell; each operating system uses a particular name for these functions including batch files (MSDos-Win95 stream, OS/2), command procedures (VMS), and shell scripts (Windows NT stream and third-party derivatives like 4NT—article is at cmd.exe), and mainframe operating systems are associated with a number of terms. Shells commonly present in Unix and Unix-like systems include the Korn shell, the Bourne shell, and GNU Bash. While a Unix operating system may have a different default shell, such as Zsh on macOS, these shells are typically present for backwards compatibility. Capabilities Comments Comments are ignored by the shell. They typically begin with the hash symbol (#), and continue until the end of the line. Configurable choice of scripting language The shebang, or hash-bang, is a special kind of comment which the system uses to determine what interpreter to use to execute the file. The shebang must be the first line of the file, and start with "#!". In Unix-like operating systems, the characters following the "#!" prefix are interpreted as a path to an executable program that will interpret the script. Shortcuts A shell script can provide a convenient variation of a system command where special environment settings, command options, or post-processing apply automatically, but in a way that allows the new script to still act as a fully normal Unix command. One example would be to create a version of ls, the command to list files, giving it a shorter command name of l, which would be normally saved in a user's bin directory as /home/username/bin/l, and a default set of command options pre-supplied. #!/bin/sh LC_COLLATE=C ls -FCas "$@" Here, the first line uses a shebang to indicate which interpreter should execute the rest of the script, and the second line makes a listing with options for file format indicators, columns, all files (none omitted), and a size in blocks. The LC_COLLATE=C sets the default collation order to not fold