how to find all lines which do not start with something

rabbit55 has asked for the wisdom of the Perl Monks concerning the following question:

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Re: how to find all lines which do not start with something by ishnid (Monk) on Sep 16, 2004 at 14:54 UTC
TIMTOWTDI - without regexp: `my @new = grep { index $_, 'QKC_' } @orig;` [download] `index` returns 0 (i.e. false) if the string starts with 'QKC_', so those lines will not be returned by `grep`	[reply] [d/l] [select]
Re^2: how to find all lines which do not start with something by ambrus (Abbot) on Sep 17, 2004 at 09:13 UTC
This is a nice trick, but I guess it will have to search through the entire line, not only the beginning, so it can be a bit slow. Possibbilities are: `my @new = grep { rindex $_, 'QKC_', 0 } @orig;` [download] or simply `my @new = grep { substr($_, 0, 4) ne 'QKC_' } @orig;` [download]	[reply] [d/l] [select]
Re^2: how to find all lines which do not start with something by gaal (Parson) on Sep 17, 2004 at 08:44 UTC
Tiny note: if you're favoring `index` over a regexp because of speed, then you should also prefer to use `grep` in comma form instead of with a BLOCK: `my @new = grep index($_, 'QKC_'), @orig;`	[reply] [d/l] [select]
Re: how to find all lines which do not start with something by Anonymous Monk on Sep 16, 2004 at 14:21 UTC
`@weeded_out = grep(!/^QKC_/, @original_array);`	[reply] [d/l]
Re: how to find all lines which do not start with something by Anonymous Monk on Sep 16, 2004 at 14:22 UTC
untested: without grep: `foreach my $line (@lines) { next if $line =~ /^QKC_/; #do something with $line }` [download] with grep: `@subset = grep(/^QKC_/, @lines);` [download]	[reply] [d/l] [select]
Re^2: how to find all lines which do not start with something by ikegami (Patriarch) on Sep 16, 2004 at 14:26 UTC
Your grep does the opposite of what it should. Add a '!' in front of /^QKC_/.	[reply]