One way that I can see how to do this is with the following subroutine called prepend_file():
#!/usr/bin/perl -w
use strict;
use IO::File;
use constant FILE => 'test.txt';
use constant DATA => "this should be the first line\n";
use constant BUFFER_SIZE => '8096';
my $fh = prepend_file(FILE, DATA, BUFFER_SIZE);
while(my $line = <$fh>) {
print $line;
}
sub prepend_file {
my $file = shift;
my $data = shift;
my $buffer_size = shift;
#Open a temporary and source file handle
my $temp_fh = IO::File->new_tmpfile
or die "Could not open a temporary file: $!";
my $fh= IO::File->new($file, O_RDWR)
or die "Could not open file ", FILE, ": $!";
#Write the first bit of data
$temp_fh->syswrite($data);
#Copy all the $data from the $fh to the temp file handle
$temp_fh->syswrite($data) while $fh->sysread($data, $buffer_size);
$temp_fh->sysseek(0, 0);
$fh->sysseek(0, 0);
#Write out the new file from the temporary file handle
$fh->syswrite($data) while $temp_fh->sysread($data, $buffer_size);
#could return anything here, I just chose the file handle just
#in case we needed to use it for something.
return $fh->sysseek(0, 0) && $fh;
}
__END__
It uses IO::File's new_tmpfile() method to create a temporary file. You then only have to deal with the single filehandle, and IO::File takes care of throwing away the temp file when you're done. I wanted to make sure it could handle most sizes of files, even those that exceed available memory, this is why I used a temporary file and not just memory/slurping.
-
Are you posting in the right place? Check out Where do I post X? to know for sure.
-
Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big>
<blockquote> <br /> <dd>
<dl> <dt> <em> <font>
<h1> <h2> <h3> <h4>
<h5> <h6> <hr /> <i>
<li> <nbsp> <ol> <p>
<small> <strike> <strong>
<sub> <sup> <table>
<td> <th> <tr> <tt>
<u> <ul>
-
Snippets of code should be wrapped in
<code> tags not
<pre> tags. In fact, <pre>
tags should generally be avoided. If they must
be used, extreme care should be
taken to ensure that their contents do not
have long lines (<70 chars), in order to prevent
horizontal scrolling (and possible janitor
intervention).
-
Want more info? How to link
or How to display code and escape characters
are good places to start.
|