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In computer programming, a usage message or help message is a brief message displayed by a program that utilizes a command-line interface for execution. This message usually consists of the correct command line usage for the program and includes a list of the correct command-line arguments or options acceptable to said program.
In Unix and Unix-like operating systems, printf is a shell builtin (and utility program [2]) that formats and outputs text like the same-named C function. Originally named for outputting to a printer, it actually outputs to standard output. [3] The command accepts a format string, which specifies how to format values, and a list of values.
Multics had a pwd command (which was a short name of the print_wdir command) [11] from which the Unix pwd command originated. [12] The command is a shell builtin in most Unix shells such as Bourne shell, ash, bash, ksh, and zsh. It can be implemented easily with the POSIX C functions getcwd() or getwd().
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.
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.
Expect is used to automate control of interactive applications such as Telnet, FTP, passwd, fsck, rlogin, tip, SSH, and others. [3] Expect uses pseudo terminals (Unix) or emulates a console (Windows), starts the target program, and then communicates with it, just as a human would, via the terminal or console interface. [4]
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script is in a file (e.g., script.txt) and invoked with sed -f script.txt inputFileName, where "inputFileName" is the input text file. The script changes "inputFileName" line #1 to "Hello, world!" and then quits, printing the result before sed exits. Any input lines past line #1 are not read, and not printed. So the sole output is "Hello, world!".