Bash Scripting Syntax

• Compare integer in bash, (for avoiding error : unary operator expected error)

if [[ $i -ge 2 ]]

• Number tables (for loop example)

for i in {1..9};
do
    for j in $(seq 1 9);
    do
        echo -ne $i×$j=$((i*j))\\t;
    done;
    echo;
done

• Test of variable is a number in bash shell script

re='^[0-9]+$'
if ! [[ $yournumber =~ $re ]] ; then
    echo "error: Not a number" >&2;
    exit 1
fi

• Remove last character of variable

something="myname"
echo ${something%?}

• Removing first character of variable

something="myname"
echo ${something#?}

• Using nested variable in bash

array=(1 2 3 4 5)
for i in ${array[@]}
do
    v=$(printf "str%s" $i)
    echo $v
done

• Redirecting eval to log file

eval ls 2>&1 > /tmp/av.log

• Converting variable string into lower case using bash

REALM="Sample.Example.COM"
echo $REALM
echo ${REALM,,}