You might also consider using split() and use its optional third parameter to tell it to only break it into two chunks.

my( $before, $after ) = split /$breakline/, $content, 2;
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If you $breakline might have regex special characters in it, you might want to escape those with either quotemeta() or the \Q.

my( $before, $after ) = split /\Q$breakline/, $content, 2;
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