A shell is a command interpreter that sits between the user or automation and the operating system. It accepts commands, performs expansions and redirections, launches programs, and reports exit status.

The source guide introduces several shells including sh, Bash, Zsh, Fish, Korn shell, Dash, PowerShell, and Ash. For this topic, we focus on Bash because it is widely available in Linux server, CI/CD, cloud, and DevOps environments.

Shell vs terminal vs kernel

These are related but different:

Engineer / Pipeline
       ↓
Terminal or automation runner
       ↓
Bash
       ↓
Commands + system calls
       ↓
Linux kernel

Interactive shell vs script

An interactive shell waits for commands. A script stores a sequence of shell commands in a file so the same automation can be executed repeatedly.

bash app.sh

A filename ending in .sh is a convention, not a Bash requirement. A script can be executable without that extension.

Why shell scripting matters for DevOps

Shell scripts are especially useful for:

• glue code between CLI tools
• deployment/bootstrap tasks
• health checks and operational diagnostics
• file/configuration manipulation
• CI/CD job steps
• backups and cleanup
• infrastructure helper scripts