shellscripts

Shell scripts are text files containing commands that are executed by a Unix-like shell to automate tasks. They are used for system administration, batch processing, and deployment, enabling repetitive or complex sequences to run without manual input.

A script begins with a shebang line that indicates the interpreter, for example #!/bin/bash. The script's behavior depends on the shell's language features. POSIX sh aims for portability across shells, while Bash, Zsh, and Ksh offer extensions.

Typical constructs include variables, conditionals (if, test), loops (for, while), and functions, along with redirection, pipelines, and sometimes arrays. Quoting and proper escaping are important to avoid word splitting and surprises.

Creating and running: make the file executable with chmod +x script, then run as ./script or sh script. Debugging options such as set -e, set -u, and set -x help identify errors and track execution.

Common use cases: automation of backups, log rotation, software installation, configuration tasks, and cron jobs. For portability, prefer POSIX-compliant syntax; many teams rely on shellcheck to catch issues and follow best practices.

Shell scripts remain a foundational tool in Unix-like environments, with a large ecosystem of utilities (awk, sed, grep) and cross-shell resources. Mastery involves understanding shell behavior, quoting, error handling, and test strategies.