Re^2: Cleaner way of looping through a file and stripping only certain lines?

>>I'm curious as to how one would go about editing the file in place, i.e., not having to create a new outfile.
>Open the file. Read the file into an array. Close the file. Open the same file for overwrite and write what you want back.

This works, but isn't it inherently risky for cases where there's a power failure or other hiccup during processing — you corrupt your original?

throop

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Re^3: Cleaner way of looping through a file and stripping only certain lines?
by grep (Monsignor) on Dec 08, 2006 at 17:34 UTC

A safer answer would be to use File::Temp. You still have a problem with power failure but your window of problems is smaller.

## UNTESTED
use File::Temp 'tempfile';
use File::Copy;
my ($tmp_FH,$tmp_fn) = tempfile();

open(IN, '<', $ifile) or die "Couldn't open file: $!\n";
my @data = <IN>;
close IN;

foreach my $line (@data) {
    ### Do what you want
    print $tmp_FH "$line";
}
copy($tmp_fn,$ifile);
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grep

XP matters not. Look at me. Judge me by my XP, do you?

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Re^3: Cleaner way of looping through a file and stripping only certain lines?
by jbert (Priest) on Dec 08, 2006 at 18:22 UTC

The rename is an atomic operation. It's guaranteed to succeed completely or not at all (on Unix-like boxes), so you can never lose data as a result of a power failure.

This is a similar trick to perl -i, but I think that does a rename of the original file and then writes back into the original file, which still leaves open the case that you could have bad (partially written) data in the original file on power failure.

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