How to convert a string to lower case in Bash?

Question

Is there a way in bash to convert a string into a lower case string?

For example, if I have:

a=\"Hi all\"

I want to convert it to:<

Answer 1

I know this is an oldish post but I made this answer for another site so I thought I'd post it up here:

UPPER -> lower: use python:

b=`echo "print '$a'.lower()" | python`

Or Ruby:

b=`echo "print '$a'.downcase" | ruby`

Or Perl (probably my favorite):

b=`perl -e "print lc('$a');"`

Or PHP:

b=`php -r "print strtolower('$a');"`

Or Awk:

b=`echo "$a" | awk '{ print tolower($1) }'`

Or Sed:

b=`echo "$a" | sed 's/./\L&/g'`

Or Bash 4:

b=${a,,}

Or NodeJS if you have it (and are a bit nuts...):

b=`echo "console.log('$a'.toLowerCase());" | node`

You could also use dd (but I wouldn't!):

b=`echo "$a" | dd  conv=lcase 2> /dev/null`

lower -> UPPER:

use python:

b=`echo "print '$a'.upper()" | python`

Or Ruby:

b=`echo "print '$a'.upcase" | ruby`

Or Perl (probably my favorite):

b=`perl -e "print uc('$a');"`

Or PHP:

b=`php -r "print strtoupper('$a');"`

Or Awk:

b=`echo "$a" | awk '{ print toupper($1) }'`

Or Sed:

b=`echo "$a" | sed 's/./\U&/g'`

Or Bash 4:

b=${a^^}

Or NodeJS if you have it (and are a bit nuts...):

b=`echo "console.log('$a'.toUpperCase());" | node`

You could also use dd (but I wouldn't!):

b=`echo "$a" | dd  conv=ucase 2> /dev/null`

Also when you say 'shell' I'm assuming you mean bash but if you can use zsh it's as easy as

b=$a:l

for lower case and

b=$a:u

for upper case.