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extract range from array of data

by theleftright (Novice)
on Dec 26, 2015 at 11:53 UTC ( #1151188=perlquestion: print w/replies, xml ) Need Help??

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

Howdy everyone and merry perlmass! blah.txt contains the following data:
junk junk junk junk start not junk not junk end junk junk
more junk
open (hFile, "blah.txt"); @d = <hFile>; close hFile;
now how would i extract only:
start not junk not junk end
from that array? thanks all :) I have looked around, all i can find is how to do this on a string, but then i risk loosing all the nowlines. p.s: would be better if this was possible in 1 line

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Re: extract range from array of data
by BrowserUk (Patriarch) on Dec 26, 2015 at 12:04 UTC

    Use the flip-flop operator:

    @d = grep{ /^start$/ .. /^end$/ } <hFile>;

    With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
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      BrowserUK you just blew my mind, thanks for the tip!

      thanks (y) perfect.
Re: extract range from array of data
by QuillMeantTen (Friar) on Dec 26, 2015 at 12:44 UTC

    Greetings,
    First, loading it all inside an array might not be a good idea, if its a very large file you are asking for trouble, why not read it line by line until you reach start, save the lines until you read end and close the file at that time?

      There's a discussion of this approach in perlfaq6: "How can I pull out lines between two patterns that are themselves on different lines?" — even a one-liner! See also the discussion of the scalar context  .. flip-flop operator in Range Operators (scalar context sub-section) in perlop (some examples of what you want there also). (Update: See also Flipin good, or a total flop?, also with code that's almost exactly what theleftright seems to want.)


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