sh

Did you mean sh as in the Unix shell (POSIX “Bourne shell” interface)?

If so, here’s the practical cheat sheet.

What sh is

• sh runs a POSIX-compatible shell (the “standard” shell language).
• On many systems, /bin/sh is not Bash:
  • Debian/Ubuntu often link /bin/sh → dash (faster, more strictly POSIX).
  • macOS commonly runs an older Bash in “sh mode,” but details vary by version.

Run a script with sh

sh
sh script.sh

Make a script executable (recommended)

1. Put a shebang on the first line:

sh
#!/bin/sh
echo "Hello"

2. Make it executable and run it:

sh
chmod +x script.sh
./script.sh

Common “safe mode” options

sh
set -eu
# -e: exit on error
# -u: error on unset variables

(“pipefail” isn’t POSIX, so it may not work in sh.)

POSIX vs Bash gotchas (quick)

If you use sh, avoid Bash-only features like:

• [[ ... ]] (use [ ... ])
• arrays arr=(a b)
• source file (use . file)
• brace expansion {1..5}

Example POSIX test:

sh
if [ -f "$1" ]; then
  echo "file exists"
fi

If you tell me what you meant by “sh” (run a .sh file? write a shell script? something else?), I’ll tailor it.