http://www.perlmonks.org?node_id=9470

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

I am out on the road, and only have a laptop (w/out Perl) so I can't test this out....
Can I erase the contents of a file this way (I don't want to unlink the file, I just want to "clean it out.": 
...
s/./\004/;
...

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Where \004 is ^D?
Simplicus

Replies are listed 'Best First'.
Re: cleaning out a file
by turnstep (Parson) on Apr 28, 2000 at 01:24 UTC
    Nope.
    But you could do this: 
    open(X, ">$filename");

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    or even: 
    perl -e "open(X, '>'.shift);" SYSTEM.DA0

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    which would shrink SYSTEM.DA0 to 0 bytes....
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      Yes, I think this is the safest way. close FH if open FH, ">".$filename But overwrite mode might do an unlink/link combo. (meaning that the file $filename might be deleted, then recreated as a empty file). So this could be the same asunlink $filename; open ">$filename"; I am not sure. Anybody actually know if there is a difference? The file inode number should still be the same though for either method.
      Depending on what you are doing this is probably good enough.
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RE: cleaning out a file
by Anonymous Monk on Apr 28, 2000 at 11:24 UTC
    system("cat /dev/null>$file");

    also not very portable

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Re: cleaning out a file
by blackwolf (Sexton) on Apr 28, 2000 at 20:50 UTC
    What about plain ol' ... 
        truncate 'filename', 0;
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Re: cleaning out a file
by clash (Novice) on Dec 01, 2000 at 23:53 UTC
    why dont u just unlink it and create it again?
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Re: cleaning out a file
by kirbyk (Friar) on Apr 28, 2000 at 02:38 UTC
    Another easy way to do it would be: 
    unlink($filename);
system("touch $filename");

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    touch is a standard unix command that updates the last-modified timestamp of a file. If the file doesn't exists, it creates it as a zero-byte file. It's a handy little thing to know, for testing purposes.

    -- Kirby

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      Actually, 'touch' does a lot more than that. Most people only use it for its default behavior, but it can change the access and modification times to anything you want - which can be occassionally very useful. For the record, using a system("touch") is not very portable, especially when you can do the same thing in perl easy enough.
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RE: cleaning out a file
by radixzer0 (Beadle) on Apr 28, 2000 at 02:33 UTC
    Hate to introduce a non-perl item ;) but a bash one-liner is:
    : > filename

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    Use the tools you've got is what i always say...
    This also preserves all the file permissions and attributes...
    Assuming you're on Unix of course (or bash on some other platform).
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