Linux Admin - Conditionals

While loops are the main control structures for operational flow, logical operations need to be performed as well.

Logical operations can be controlled with the following constructs in BASH: if, then, else, and elif.

If

This is pretty simple and will make a conditional operation based on how a logic test evaluates.

#!/bin/bash
result = 1

if [ $result -eq 1 ];  
   then 
   echo "Result was true!" 
else  
   echo "Result was false!" 
fi

Note − Bash uses a few different equality operators. In this case, we used "-eq", performing equality on an integer. For a string, we'd use "==".

elif is used to pass logic to another conditional branch, shown as follows −

#!/bin/bash 
ourColor="red" 
if [ $ourColor == "black" ]; 
   then 
   echo "Too dark" 
elif [ $ourColor == "white" ]; 
   then 
   echo "Too plain!" 
elif [ $ourColor != "gray" ]; 
   then 
   echo "Too colorful"
else 
   echo "Let's make it" $ourColor 
fi

Our somewhat biased script will not be satisfied until we decide on gray.