How to check if sed has changed a file

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A bit late to the party but for the benefit of others, I found the ‘w’ flag to be exactly what I was looking for.

sed -i "s/$pattern/$new_pattern/w changelog.txt" "$filename"
if [ -s changelog.txt ]; then
    # CHANGES MADE, DO SOME STUFF HERE
else
    # NO CHANGES MADE, DO SOME OTHER STUFF HERE
fi

changelog.txt will contain each change (ie the changed text) on it’s own line. If there were no changes, changelog.txt will be zero bytes.

A really helpful sed resource (and where I found this info) is http://www.grymoire.com/Unix/Sed.html.

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