Try one of these one-liners (they have the same output, but I thought the second might be a little easier to understand):

perl -ple '($_) = /^\S+/g' filename
perl -ple '$_ = (/^\S+/g)[0]' filename
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Basically, it reads a line, then sets it to the first group of non-whitespace stuff at the beginning of the line, and then prints the changed line out. Hope this helps!

His Royal Cheeziness