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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.
Here documents are available in many Unix shells. [1] In the following example, text is passed to the tr command (transliterating lower to upper-case) using a here document. This could be in a shell file, or entered interactively at a prompt.
Microsoft Windows [10] ReactOS [11] HP MPE/iX [12] KolibriOS [13] SymbOS; Unix and Unix-like operating systems; Many shells, including all Bourne-like (such as Bash [14] or zsh [15]) and Csh-like shells as well as COMMAND.COM and cmd.exe implement echo as a builtin command. The command is also available in the EFI shell. [16]
In the case of multiple possible completions, some command-line interpreters, especially Unix shells, will list all possible completions beginning with those few characters. The user can type more characters and press Tab ↹ again to see a new, narrowed-down list if the typed characters are still ambiguous, or else complete the command ...
While Bash was developed for UNIX and UNIX-like operating systems, such as GNU/Linux, it is also available on Android, macOS, Windows, and numerous other current and historical operating systems. [12] "Although there have been attempts to create specialized shells, the Bourne shell derivatives continue to be the primary shells in use."
Shell functions, especially if the command being created needs to modify the internal runtime environment of the shell itself (such as environment variables), needs to change the shell's current working directory, or must be implemented in a way which guarantees they it appear in the command search path for anything but an interactive shell ...
On earlier versions, such as Windows 2000 or Windows NT 4.0, the maximum length of the string is 2047 (2 11-1) characters. This limit includes the command line, individual environment variables that are inherited by other processes, and all environment variable expansions. [10] Quotation marks are required for the following special characters: [8]
read is a command found on Unix and Unix-like operating systems such as Linux. It reads a line of input from standard input or a file passed as an argument to its -u flag, and assigns it to a variable. It is built into shells such as Bash. [1]