asked on

deleting data in text file

well, i have a homepage whereby users can key in data and that data will automatically be in my text file. i use pipe and the sample of the text file is like this:

aa|bb|cc|dd
ee|ff|ggg|fdg
rr|fdg|tfh|fcbv

from the web, user has to enter for fields, and that data will be inserted in the text file as above. it's working as what i wanted.
the problem is when i want to delete let's say the second row, how could i do it? can i do so? should i replace that row to blank? is there any delete command in perl??
answer with coding is really appreciated.
bye

Kim Ryan

It's a common question and has been covered in the Perl FAQ:
http://www.perl.com/pub/doc/manual/html/pod/perlfaq5.html#How_do_I_change_one_line_in_a_fi

cadabra

You will need a synchronization mechanism, to serialize access to the file;

See Win32::Mutex , if you are using activestate perl (on windows platform).

ASKER CERTIFIED SOLUTION

TYoung

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kudak

ASKER

ok tyoung. let's say i that data is keyed in by the user. is it going to be

open(FILE, "file.txt");
my(@lines) = <FILE>;
close(FILE);

$LineToDelete = '(FORM{name} eq "xx") && (FORM{address} eq "zz"';

$Numbs = @lines;

open(FILE, ">file.txt");
for($i = 0; $i < $Numbs - 1; $i++) {
print FILE @lines[$i] unless ($i = ($LineToDelete - 1));
}
close(FILE);

thanks.

TYoung

Okay, then you would want something like this:

open(FILE, "file.txt");
      my(@lines) = <FILE>;
close(FILE);
my($i) = 0;
foreach (@lines) {
      $FILELINES{$_} = $i + 1;
      $i++;
}
my($LTD) = $FORM{'name'} . "|" . $FORM{'address'} . "\n";
$LineToDelete = $FILELINES{$LTD};
$Numbs = @lines;
open(FILE, ">file.txt");
for($i = 0; $i < $Numbs - 1; $i++) {
print FILE @lines[$i] unless ($i = ($LineToDelete - 1));
}
close(FILE);

Again.. this is untested...

cadabra

how about using grep() to remove the unwanted lines from @lines ...

TYoung

If you use grep, you may delete some line of a person that has the same first name, or same zip code, or something like that.

ozo

#You could grep for the same condition you're testing in your for loop
#or
{local $^I=$$; local @ARGV=("file.txt");
while( <> ){ print unless /^\Q$FORM{name}|$FORM{address}|\E/ }
}