Convert case in Bash

tr

$ echo $a | tr '[:upper:]' '[:lower:]'

hi all

AWK

$ echo $a | awk '{print tolower($0)}'

hi all

Bash 4.0

$ echo ${a,,}

hi all

Perl

$ echo $a | perl -ne 'print lc'

hi all

Bash

lc(){

    case "$1" in

        [A-Z])

        n=$(printf "%d" "'$1")

        n=$((n+32))

        printf \\$(printf "%o" $n)

    esac

}

word="ABX"

for((i=0;i<${#word};i++))

do

    ch=${word:$i:1}

    lc $ch

done