I don't see any problem with labeling lines with something descriptive. I do this in my code because it makes the meaning more legible in standard English. However, I would omit the semicolon in the else clause, so it would read

    else {$flag = 0}
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I typically use such one-line blocks in evals like

eval {this_may_die();};
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Removing all the unnecessary punctuation makes it much nicer, in my opinion:

eval {this_may_die};
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