m/\S=\S| =\S|\S= /g
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Since you are concerned about readability, here is what I would prefer ... not that everyone thinks like me, but at least you have one more option :-)

# Bad: m/[\S ]=[\S ]/g
m/(?!: = ).=./gs
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Update:I should not post this early ... I misread the specs. Without doing capturing braces (and you don't want that, I gather), I can do no better than your version.

Update 2:Added the negative lookahead version.

The Sidhekin
print "Just another Perl ${\(trickster and hacker)},"