Just for fun:

while (<FILE>) {
    print if ( /^(\d+)/ && $1 == 1);
}
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Oughta do the job too.

(Explanation: if the expression matches, i.e. if there are one or more digits at the beginning of the line, then that sequence of digits will be saved in $1, and then the right-hand-side of the conjunction will be evaluated).

Philosophy can be made out of anything. Or less -- Jerry A. Fodor