perl -pi~ -e 's/oh/Ohio/g'; Try reading perlre and perlrun (pay special attention to -i), they ought to give a thorough explanation of what goes on there. Suffice it to say -p makes perl act like a stream editor (sed). UPDATE: To clarify that doesn't make perl act like *the* sed though.

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perl -pe "s/\b;([st])/'\1/mg"