in reply to Skipping the first 4 lines of a file:: Is there a better way?

If the size of the file is not a concern: 
...

my $skip = 4;

{
    open FH, "filename";
    local@_ = <FH>;
    close FH;
    @_ = split /(?:.+\n){$skip}/m, "@_";
    for( @_ ){
        # work without first four lines 
    }
}
...

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Re^2: Skipping the first 4 lines of a file:: Is there a better way?
by Fletch (Bishop) on Jun 03, 2005 at 14:22 UTC 
    @_ = split /(?:.+\n){$skip}/m, "@_";

    [download]

    Gah, that's terribly inefficient. splice( @_, 0, $skip ) at the least if you feel you have to modify @_. foreach( @_[  $skip .. $#_ ] ) { ... } would be even better since it doesn't have to move anything around.

    Update: Changed from hardcoded 4 to $skip to match.

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Re^2: Skipping the first 4 lines of a file:: Is there a better way?
by fishbot_v2 (Chaplain) on Jun 03, 2005 at 15:02 UTC

    Efficiency aside, does this really work? Okay, well, I know the answer: it doesn't. There is no limit on the split, and the delimiter is any {4} lines.

    So, if my file is 10 lines long, I get two empty strings, then the remaining 2 lines. Infact, you only ever end up with the last X lines of your file (where X = lines % $skip), preceeded with (lines div $skip) empty strings. 

    @_ = split /(?:.+\n){$skip}/m, "@_", 2;  # add limit
# closer, but now I have @_ == 2, 
# since there is a leading null

shift @_;
# now I have a single element array with 
# the file remainder in $_[0]

@_ = split /\n/, $_[0];
# now I have the desired results.

    [download]

    I agree that solutions don't always need to be the most efficient, but parsing through the entire file at least three times is O(n) where O(1) is available in a single line of code.

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