FIND AND REPLACE TEXT WITHIN A FILE USING SED COMMAND

The is a test file created by nixCrft for demo purpose.

foo is good.

Foo is nice.

I love FOO.

sed 's/foo/bar/g' hello.txt

OUTPUT:

The is a test file created by nixCrft for demo purpose.

bar is good.

Foo is nice.

I love FOO.

To match all cases of foo (foo, FOO, Foo, FoO) add I (capitalized I) option as follows:

sed -i 's/foo/bar/gI' hello.txt

OUTPUT:

The is a test file created by nixCrft for demo purpose.

bar is good.

bar is nice.

I love bar.