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sh Command Cheat Sheet

sh is the command name for the Bourne shell (or a compatible interpreter). It is the standard command language interpreter for Unix-like systems.

On Linux: /bin/sh is usually a symlink to bash (Red Hat) or dash (Debian/Ubuntu).

Synopsis

sh [options] [file]

Basic Usage

Run a Script

sh script.sh
This forces the script to be interpreted by sh, ignoring any logic that relies on bash specific extensions (like arrays [] or C-style loops (())).

Read from Stdin

sh -s < commands.txt

Inline Command (-c)

Execute a command string.

sh -c "echo Hello; date"

sh vs bash

sh aims for POSIX compliance. bash adds many non-standard features (Arrays, String manipulation, process substitution).

Feature sh (POSIX) bash
Arrays No Yes (arr=(a b))
Brace Expansion No Yes ({1..10})
Test [ ] [[ ]] (Safer)
String Replace sed needed ${var/a/b}
Math expr (( i++ ))
Here String No Yes (<<<)

When to use sh?

  1. Portability: Script must run on any Unix (AIX, Solaris, BSD, Alpine Linux).
  2. Speed: dash (Debian's sh) is much faster and lighter than bash (faster boot scripts).
  3. Shebang: #!/bin/sh implies simple, standard code. #!/bin/bash implies features.

Debugging

See what the shell is doing.

  • -x: Print commands and arguments as they are executed.
  • -n: Read commands but do not execute (syntax check).
  • -e: Exit immediately if a command exits with a non-zero status.
# Debug a script
sh -x ./deploy.sh

Notes

  • Symlink Check: Check what your system uses. 
    ls -l /bin/sh
# lrwxrwxrwx 1 root root 4 /bin/sh -> bash