The constant form of the flip-flop only operates against $.. Ie. The line number of the current file being read. Hence the first loop below produces the output expected, but the second does not. 

#! perl -slw
use strict;

while( <DATA> ) {
    print if 1..4;
}

for ( 1 .. 8 ) {
    print if 1..4;
}


__DATA__
line 1
line 2
line 3
line 4
line 5
line 6
line 7
line 8

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In reply to Re^2: modifying a string in place by BrowserUk
in thread modifying a string in place by davidj

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