Writing to a file: problem

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

Hi folks,

When I run the following script, the code runs but an unitialised print value is declared. I run it again and the entire file I'm writing to is erased! What am I missing?

#!/usr/bin/perl
# addwordspacing3.plx
=head1 DESCRIPTION

Program will read in an html file, append word spacing attribute to th
+e in-line style
and print in DOS window.

=cut

use warnings;
use diagnostics;
use strict;

# Open HTML test file - forward slashes do not need to be escaped.
open INFILE, "E:/Documents and Settings/Richard Lamb/My Documents/HTML
+/dummy.html" or die "$!: Can't open this file.\n";

while (<INFILE>)
{
    s/(<h[1-6]\s+style=.*)">/$1; word-spacing: 50px">/ig;
    s/(<li\sstyle=.*)">/$1; word-spacing: 20px">/ig;
    s/(<p style=.*)">/$1; word-spacing: 20px">/ig;
    print;
}

close (INFILE);
open (OUTFILE, ">E:/Documents and Settings/Richard Lamb/My Documents/H
+TML/dummy.html") or die("$!: Can't write to the HTML file.\n");
print (OUTFILE);
close (OUTFILE);
[download]

Comment on Writing to a file: problem Download Code

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Re: Writing to a file: problem by tcf22 (Priest) on Sep 04, 2003 at 14:30 UTC
The following code is opening the file for writing(thereby erasing the contents), but really printing nothing to it `open (OUTFILE, ">E:/Documents and Settings/Richard Lamb/My Documents/H +TML/dummy.html") or die("$!: Can't write to the HTML file.\n"); print (OUTFILE); close (OUTFILE);` [download] I think this may be what you want. Printing to the outfile in the loop `open (OUTFILE, ">E:/Documents and Settings/Richard Lamb/My Documents/H +TML/dummy.html") or die("$!: Can't write to the HTML file.\n"); while (<INFILE>) { s/(<h[1-6]\s+style=.)">/$1; word-spacing: 50px">/ig; s/(<li\sstyle=.)">/$1; word-spacing: 20px">/ig; s/(<p style=.*)">/$1; word-spacing: 20px">/ig; print OUTFILE $_; } close (OUTFILE);` [download]	[reply] [d/l] [select]
Re: Writing to a file: problem by broquaint (Abbot) on Sep 04, 2003 at 14:32 UTC
Your problem is that you're opening the file for reading, printing out the modified data to `STDOUT` and then opening it for writing which truncates it. What you probably want is something like this my $path = "E:/Documents and Settings/Richard Lamb/My Documents/HTML"; open INFILE, "$path/dummy.html" or die "$!: Can't open this file"; open OUTFILE, ">$path/new_dummy.html" or die "$!: Can't write to the HTML file"; while (<INFILE>) { s/(<h[1-6]\s+style=.)">/$1; word-spacing: 50px">/ig; s/(<li\sstyle=.)">/$1; word-spacing: 20px">/ig; s/(<p style=.*)">/$1; word-spacing: 20px">/ig; print OUTFILE $_; } close INFILE; close OUTFILE or die "$0: $!"; rename "$path/new_dummy.html", "$path/dummy.html" or die "$0: $!"; [download] This way you're writing to the output file as you're modifying the data from the input file (not the input file itself) and once that's finished you replace the input file with the output file. See. `open`, `perlopen` and `rename` for more info on the functions used. HTH `_________ broquaint`	[reply] [d/l]
Re: Writing to a file: problem by gjb (Vicar) on Sep 04, 2003 at 14:28 UTC
In the `print (OUTFILE);` you just print the empty string to the file you've just read from. So its content will be empty after you close the file. You'd better open a temp file to print to and rename it later to the original file's name. File::Temp might help. Hope this helps, -gjb-	[reply] [d/l]
Re: Writing to a file: problem by Abigail-II (Bishop) on Sep 04, 2003 at 14:33 UTC
The line: `print (OUTFILE);` [download] prints $_ to the filehandle. But what is $_? It's set by the while loop, so it has the value of the last time the while was checked. Which was at the end of the file, and hence $_ is undefined. That's why you get your warning, and that's why the file is empty - undef stringified gives you the empty string. Abigail	[reply] [d/l]
Re: Writing to a file: problem by zby (Vicar) on Sep 04, 2003 at 16:03 UTC
You might consider using the `-i` switch to the perl interpreter for such editing. Type `perldoc perlrun` for documentation.	[reply] [d/l] [select]