Shell Scripting: Expert Recipes for Linux, Bash, and More

elif

elif is a construct that allows you to add conditions to the else part of an if statement. It is short for “else if” so that a long string of possible actions can be written more concisely. This makes it easier to write, easier to read, and most importantly, easier to debug. A common task for a multi-platform script (such as a generic installer for various different Unixes) is to perform some parts of its task differently depending on the actual operating system it is running on. Without even including any of the actual platform-specific code, this is clearly a mess to read, edit, and debug.

#!/bin/bash
OS='uname -s'
if [ "$OS" = "FreeBSD" ]; then
  echo "This Is FreeBSD"
else
  if [ "$OS" = "CYGWIN_NT-5.1" ]; then
    echo "This is Cygwin"
  else
    if [ "$OS" = "SunOS" ]; then
      echo "This is Solaris"
    else
      if [ "$OS" = "Darwin" ]; then
        echo "This is Mac OSX"
      else
        if [ "$OS" = "AIX" ]; then
          echo "This is AIX"
        else
          if [ "$OS" = "Minix" ]; then
            echo "This is Minix"
          else
            if [ "$OS" = "Linux" ]; then
              echo "This is Linux"
            else
              echo "Failed to identify this OS"
            fi
          fi
        fi
      fi
    fi
  fi
fi

elif1.sh

By using elif, you can make this much simpler, which not only helps the readability, but makes the script an ...