How to make variable values UPPERCASE or lowercase in Bash

When we need to transform some Bash variable value into, for example, uppercase, we often use some pipelines like the followings:

foo="foo"

foo=$(echo ${foo} | tr a-z A-Z)

or using AWK:

foo=$(echo ${foo} | awk '{print toupper($0)}')

or with Perl:

foo=$(echo ${foo} | perl -ne 'print uc')

or using sed:

foo=$(echo ${foo} | sed 's/[a-z]/\U&/g')

However, it is possible to achieve the same results just using pure Bash! And it's fantastically easy to do!

Let's start with defining the variable and its value:

foo="foo"

Now let's make the very first letter (f) uppercase — F:

foo=${foo^}
echo $foo
Foo

Cool! Let's now make the first letter back to lowercase:

foo=${foo,}
echo $foo
foo

Splendid! Let's make all letters uppercase:

foo=${foo^^}
echo $foo
FOO

Terrific! And back to the all lowercase again:

foo=${foo,,}
echo $foo
foo

That's all! I hope you find this post educational! Happy scripting!