Some useful bash features

bash_tricks.sh

#!/usr/bin/env bash

set -eux

#e - error if non zero return value
#u - undefined variables trigger syntax error
#x - debug
#minus sign ADDS the flags
#plus sign REMOVES the flags


A=7
#Double parenthesis after $ performs arithmetic 
B=$(($A * 4))
echo $B


#Double parenthesis in if statements allow arithemtic comparison
if (( $B > 25 ))
then
    echo $B
    echo ${C:-$((B+10))}
fi


set +u

#Double brackets allow proper variable usage not expansion
if [[ $1 == "thing" ]]
then
    thing="Oops no args"
else
    thing=$1
fi

set -u


#Default value
echo ${1:-"Oops no args"}