Hi,

Tie::File may be of your choice. It fetches file line-by-line to an array. Whatever you do with the array will reflect in the file like editing, adding or deleting a line. They say :

Tie::File represents a regular text file as a Perl array. Each element in the array corresponds to a record in the file. The first line of the file is element 0 of the array; the second line is element 1, and so on. The file is not loaded into memory, so this will work even for gigantic files. Changes to the array are reflected in the file immediately.

You can push, pop, shift and unshift the array to append, delete from end, delete from beginning and add at beginning. Splice on array can remove a line from array :)

Cheers !

--VC

Thanks a lot for your help

It's not clear to me whether you want to append to the file b.txt or whether you want to overwrite it. See open for the various parameters you can pass to the open function to tell it what it should do to the file b.txt.

Hi,
I want to over write data in a.txt.
I am expecting output in a.txt as


Thisisatestline
Containsvalues
TestingTestinginProgress

Currently I am reading a.txt, store those data in an array.
Then creating b.txt and replacing NULL and spaces from a.txt.
Finally replacing a.txt by b.txt using mv command.

Can you please provide best method to handle this?
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Thanks

This doesn't sound too bad to me. Especially, your solution is safe from errors if your program crashes before the new output has been written completely. Why are you trying to change that?

system("mv b.txt a.txt");
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rename('b.txt', 'a.txt');
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Thanks

hello fellow monk,

yes there is a facility in perl to modify a file (i.e. to do inline replacement)

 perl -pi -e 's/MONK/SAINT/ig' abc.txt

The above file will replace all the instances of MONK to SAINT in the file abc.txt

hope it helps,

Blessings,
a perl Monk

I think you forgot to create a backup of the file. I tried:

perl -pi -e 's/MONK/SAINT/ig abc.txt
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and get:

Can't do inplace edit without backup.
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If you change that to:

perl -pib -e 's/MONK/SAINT/ig' abc.txt
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Then it works ;)

---

Smoothie, smoothie, hundre prosent naturlig!

Actually, just specifying -i will work on most platforms. Cf perldiag :


       Can’t do inplace edit without backup
           (F) You’re on a system such as MS-DOS that gets confused if
+ you try
           reading from a deleted (but still opened) file.  You have t
+o say
           "-i.bak", or some such.
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Here's another way: Open the file in "update mode", which lets you read and write at the same time. Read everything in and modify as before, then rewind the file pointer back to the beginning, write out the modified content, then close the file. The trick here is that if the new version is shorter than the original, you need to trim off the extra stuff on the end - that's what 'truncate' does. This will let you modify the file in place, with no backup. But it does assume that everything can be slurped into memory at one time, so it won't scale well for large input files.

use strict;

# open in read/write mode
open(DATA, "+< a.txt") or die "Cannot read $!";
my @info = <DATA>;
foreach (@info) {
  $_ =~ s/NULL//g;
  $_ =~ s/ //g;
}

seek(DATA, 0, 0); # rewind back to beginning

foreach(@info) {
  print DATA;
}

truncate(DATA, tell(DATA));
close(DATA);
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