Shellscript

Shellscript, commonly referred to as shell scripting, is the practice of writing programs for a command-line shell to automate tasks on Unix-like systems. A shell script is a plain text file that contains a sequence of commands, variable assignments, and control structures. When run, the shell reads the script and performs the defined actions line by line. Most scripts start with a shebang line, e.g., #!/bin/sh or #!/usr/bin/env bash, which selects the interpreter.

Common shells include sh (Bourne shell), Bash, Zsh, Ksh, and Dash. Bash remains the most widely used for scripting, while POSIX sh aims for portability across systems. Scripts written for posix sh tend to work on many environments, but shells provide extensions that can affect portability.

Shell scripts commonly implement variables, conditionals (if, case), loops (for, while, until), functions, and command substitution. They support redirection and pipes, process substitution in some shells, and arrays in some implementations. They rely on exit statuses to indicate success or failure and can enable strict error handling with options such as set -e, set -u, and set -o pipefail.

Uses include system administration tasks, batch processing, startup and maintenance scripts, and build or deployment pipelines. When portability is important, POSIX-compliant syntax is preferred and Bash-specific features are avoided. Good practices include quoting expansions, avoiding unquoted variables, testing with portable constructs, and documenting behavior through comments.