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Re: search for a pattern in file without opening the file

by tinita (Parson)
on Jan 29, 2007 at 09:57 UTC ( #597052=note: print w/ replies, xml ) Need Help??


in reply to search for a pattern in file without opening the file

i want to search for a pattern inside these files without opening these files.
well... you have to use the module Crystal::Ball which is very good in guessing what's in a file.

seriously, how do you want to know the contents of a file without opening it?


Comment on Re: search for a pattern in file without opening the file
Re^2: search for a pattern in file without opening the file
by holli (Monsignor) on Jan 29, 2007 at 10:01 UTC
Re^2: search for a pattern in file without opening the file
by reasonablekeith (Deacon) on Jan 29, 2007 at 10:51 UTC
    Shame on you tinita, -- for such bad advice...

    He'd be much better of using Quantum::Schrodingers_Cat. The major plus side of using this module is that you can just choose the result you want. He may not even need to run the script, which has obvious efficiency advantages. :p

    ---
    my name's not Keith, and I'm not reasonable.

      Hmmm, Quantum::Schrodingers_Cat sounds like a Damian module. This computer is alive or dead depending on the XOR of this entire file - a new variant to the halting problem.

      How about another application: "This file/email attachment contains a virus" without opening it.

      --

      Oh Lord, won’t you burn me a Knoppix CD ?
      My friends all rate Windows, I must disagree.
      Your powers of persuasion will set them all free,
      So oh Lord, won’t you burn me a Knoppix CD ?
      (Missquoting Janis Joplin)

Re^2: search for a pattern in file without opening the file
by perl-diddler (Hermit) on Jan 29, 2007 at 22:38 UTC
    In the spirit of "thinking outside the box"...*cough*...

    You would need to:
    1) know what type of file-system your files reside on.
    2) Open the device (note: not opening the file!)
    3) interpret the file system structure to find the blocks corresponding to your file on disk
    4) retrieve the file blocks corresponding to the file and perform your search on the data in memory.
    ---
    Of course you can search multiple files on the same disk, using the same device handle, so of course you save yourself the overhead of multiple "open" calls.

    Note: this likely would not work if the file was a remote (networked) file.
    Note 2: This would likely be quite painful, but if you're into that sort of thing...:-)

    As others have said, within the definition of your problem is an "inherent" open to be able to look into the contents of the file. What are you trying to do that you want to avoid opening the file in perl?

    FWIW, I'd change Ted's answer, above, to use "pcregrep" instead of "grep" to maintain use of perl-compatible regular expressions :-).

    p.s. -- sometimes you just have to put on your hat of "literalness" :-)

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