Shell scripting

• passing arguments
• if-else, case
• loops
• string, numbers, arrays
• functions, local variables
• expressions and operators
• testing, debugging
• process substitution
• traps
• wait eval, named pipes

Shebang

• Always use specific shell instead if generic /bin/sh symlink
  • since it can point to any shell

#/bin/bash

• use /usr/bin/env for maximum portability
  • since shell executables can be at other place in different OS like FreeBSD
  • This searches shell binary in PATH

#/usr/bin/env bash

Make script executable

# just make it executable
chmod +x script.sh
 
# make it executable for all users
# nobody except you can change the code
chmod 755 script.sh
 
# make it executable for current user only
chmod 700 script.sh

Script file location

• System wide
  • /usr/local/bin
• Single user
  • ~/bin
  • ~/.local/bin

check if a file exists

if [ -e "db/restore-db.sh" ]; then
  echo "Yes"
else
  echo "No"
fi