This one gives the same result as BrowserUk's 24 but is two strokes less:

perl -nE "$s^=$_}{say length$s"
perl -lpe "\$Z[y///c]}{$_=@Z"
perl -nE "\$Z[y///c]}{say$#Z"    # update: alternative 22
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Instead of finding the maximum length by exploiting Perl's wonderful bitwise string operator, we instead exploit Perl's marvellous autovivification (exploiting autovivification is common in golf, as was done by Jasper in The golf course looks great, my swing feels good, I like my chances (Part V), for example).

For golf historians, notice that the use of y///c instead of length is known as Abigail's length horror but was actually first invented by Joseph N Hall in 1996. And the use of a (one stroke) reference \ to trigger autovivification is known as Thelen's Device and was invented by Michael Thelen aka thelenm in 2002. This history is discussed in The Lighter Side of Perl Culture (Part IV): Golf.

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