Podcast #128: We chat with Kent C Dodds about why he loves React and discuss what life was like in the dark days before Git. Listen now.
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Perl: 35 characters

$_="He12o wor3d!\n";s{\d}{l}g;print

Sample run:

bash-4.1# perl -e '$_="He12o wor3d!\n";s{\d}{l}g;print'
Hello world!

(Not a big deal. Posted just to use at least once in my life s/// with those fancy delimiters.)