conditionals.sh

#!/bin/bash

# Make the script to abort if any command fails. Use set +e to change the behaviour and ignore failed command.
set -e

# Uncomment below line to print the commands as it is executed. Useful for debugging. Use set +x to disable debugging.
# set -x

echo "Example of numerical comparison with if elif else"
for (( c=-5; c<=5; c=$c+1 ))
do  
    if [[ $c -lt -4 ]]
    then
        echo "$c is less than -4"
    elif [[ ($c -ge -4) && ($c -le -1) ]]
    then
        echo "$c is greater than or equal to -4 and less than or equal to -1"

    elif [[ $c -eq 0 ]]
    then
        echo "$c is equal to 0"
    elif [[ ($c -ge 1) && ($c -le 4) ]]
    then
        echo "$c is greater than or equal to 1 and less than or equal to 4"
    elif [[ $c -gt 4 ]]
    then
        echo "$c is greater than 4"
    fi
done

echo "Example of string comparison"

if [[ "ab" == "ab" ]]
then
    echo "'ab' is equal to 'ab'"
fi

if [[ "ab" != "ba" ]]
then
    echo "'ab' is not equal to 'ba'"
fi

REGEX='^ab.*$'
if [[ "abc" =~ $REGEX ]]
then
    echo "'abc' matches regex '^ab.*$'"
fi

if [[ ! ("bac" =~ $REGEX) ]]
then
    echo "'bac' doesn't match regex '^ab.*$'"
fi

echo "Example of and (&&) or (||) not (!)"
if [[ (2 -gt 0) && (2 -gt 1) ]]
then
    echo "2 is greater than 0 and 1"
fi

if [[ (2 -gt 3) || (2 -gt 1) ]]
then
    echo "2 is not greater than 3 but 2 is greater than 1"
fi

if [[ (! (2 -gt 3) ) && (! (2 -gt 4) ) ]]
then
    echo "2 is not greater than 3 and 2 is not greater than 4"
fi