🌐 The Shell Landscape

Not all shells are equal. Understanding the differences is critical for writing portable scripts.

🏆 The Main Contenders

Shell	POSIX¹	Default On	Vibe / Use Case
sh (Bourne)	✅ Yes	Alpine, Minimal Linux	The granddaddy. Strict, portable, minimal.
bash (Bourne Again)	⚠️ Mostly	Most Linux distros	The industry standard. Powerful but full of "bashisms".
zsh (Z Shell)	⚠️ Mostly	macOS, Kali	Modern, plugin-heavy, great for interactive use.
dash (Debian Almquist)	✅ Yes	Debian/Ubuntu (/bin/sh)	Fast, lightweight, strictly POSIX.
fish (Friendly)	❌ No	N/A (User install)	Beautiful, auto-suggestions, non-standard scripting.
ksh (Korn)	⚠️ Mostly	AIX, Solaris	Legacy enterprise UNIX.

🔗 The /bin/sh Trap

On modern systems, /bin/sh is often a symlink, not a real shell.

$ ls -l /bin/sh
/bin/sh -> dash   # On Ubuntu/Debian (POSIX mode)
/bin/sh -> bash  # On RHEL/CentOS (POSIX mode)

⚠️ DevOps Rule: Never assume sh is bash. If you write #!/bin/sh, you are promising to only use POSIX features.

🛠️ Check Your Shell

echo $0        # Current shell name
echo $SHELL    # Your default login shell

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¹ POSIX: A family of standards for maintaining compatibility between operating systems.