How do I write to a file?

[vroom]

How do I write to a file?

Originally posted as a Categorized Question.

[revdiablo]

The 3-arg form of open is fairly useful to prevent problems with filenames "tricking" perl, and other nasty surprises:

open FH, ">", $outfile or die "Error writing '$outfile': $!\n";
print FH $output;
close FH;

Also useful are lexical filehandles:

open my $filehandle, ">", $outfile or die "Error writing '$outfile': $
+!\n";
print $filehandle $output;
close $filehandle;

[devslashneil]

The Tie::File module can be used to bind an array to a file.

Any changes you make to the array are then made retrospectivly to the file, without having to load the file into memory.

This is especially useful for large files
ex.

#!/usr/bin/perl
use strict;
use Tie::File;
my @array;
my $filename = 'foo.dat';
tie @array, 'Tie::File', $filename or die "Error: Cannot open $filenam
+e\n";
push @array, "Hello, World!\n";

[Crulx]

The open command opens a file. The first few characters of the second argument tell you how the file is opened. This code

open FH , ">$output_file";

truncates and opens a file for writing. All the contents are lost.

open FH, ">>$output_file";

Opens a file for appending. When you start writing to this file, it will write to the end. To actually WRITE to that file you use the print command

print FH "I will print this to a file\n";

[DigitalKitty]

A good idea when writing to a file is to include a space between the filename and the direction symbol. Like this:



open(FH, "> sample.txt") or die("Cannot write to file: $!\n");


Perl will ignore the extra space between the '>' and the filename. It is useful in preventing unexpected results.
-DigitalKitty

[chromatic]

Always, ALWAYS check the return value of a command such as open: open INPUT "myfile.txt" || die "Cannot open file: $!"; This will save you hours of aggregate troubleshooting when your program fails silently. (The special variable $! contains the error message. Print it to discover why the file couldn't be opened.)

[I0]

#I think you meant either
open INPUT, "myfile.txt" or die "Cannot open file: $!";
#or
(open INPUT, "myfile.txt") || die "Cannot open file: $!";
#"myfile.txt" || die "Cannot open file: $!"  is always true