Bash shell scripting "IF THEN" logic

UBUNTU LINUX bash shell script file. Usage of the DU and LS commands. This file is an example of scripting logic "IF THEN" & script command arguments.
project:pitch-forks filename: Script
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#!/bin/bash
if [[ $1 = "" ]]; then
echo "Usage: $0 size listing"
echo "Ubuntu Linux bash script by Johnny Buckallew Stroud 2008,"
echo "open public information. "
exit
fi

if [[ $2 = "size" ]]; then
du -h $1
exit
fi

if [[ $2 = "listing" ]]; then
ls -l $1
exit
fi

ls -l $1
du -h $1