file manipulation in perl

[Rickead2000]

HI,

is it possible to open a file in perl and change the contents of just one line?

opening it for overwrite appears to make the file blank.

if i open it in append mode, can it only write to the end of the file?

ideally, i would like to be able to overwrite JUST the line that the file pointer is currently at. e.g.

hello123
hello345 <-pointer here
hello567


is it possible to replace just the line "hello345" without affecting the rest of the file?

[takshaka]

Old perlfaq5 answer: How do I change one line in a file/delete a line in a file/insert a line in the middle of a file/append to the beginning of a file? (http://www.perldoc.com/perl5.6/pod/perlfaq5.html#How-do-I-change-one-line-in-a-file-delete-a-line-in-a-file-insert-a-line-in-the-middle-of-a-file-append-to-the-beginning-of-a-file-)

New perlfaq5 answer: use Tie::File (http://www.perldoc.com/perl5.8.0/lib/Tie/File.html)

[Rickead2000]

using the tie::file method i have put

tie @nums, 'Tie::File', $file or dienice("Error! Cannot open $file #!");

but when it gets to this line, it just appears to stop execution.

i nolonger get the following web page printed, just a white screen.

if i rem this line out, all works fine.

i have also untied the array, but to no effect.

does anyone know what it causing this?

[Hangdog42]

How about a more generic solution:

open(IN, filename);
@fileArray = <IN>;
close(IN);

If you know which line you need to change (x) you can do it with

$fileArray[x] = changedline;

Then just write out the array to a file with the same name

open(OUT,">filename");
foreach $a (@fileArray){
print(OUT $a);
}
close(OUT);

[takshaka]

Originally posted by Rickead2000
tie @nums, 'Tie::File', $file or dienice("Error! Cannot open $file #!");

but when it gets to this line, it just appears to stop execution.
Unless you've omitted the 'use Tie::File;' line, I can't guess without an error message. You'll have to look in the server's error log since this is apparently a CGI script.

btw--that should be $! instead of #!.
Originally posted by Hangdog42
foreach $a (@fileArray){
print(OUT $a);
}
No need for the loop:
print OUT @fileArray;