mkdir bak/ ; perl -pi'bak/*' -e 's/foo/bar/g' file1 file2 file3 ...

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perl -pi'bak/*' -e 'BEGIN { mkdir($^I =~ m!(.*/)!) } s/foo/bar/g' file1 file2 file3 ...

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perl -MFile::Path -pi'bak/*' -e 'BEGIN { mkpath [ $^I =~ m!(.*/)! ] } s/foo/bar/g' file1 file2 file3 ...