I want to add a text on the top of my data.txt file, this code add the text at the end of the file. how I can modify this code to write the text on the top of my data.txt file. thanks in advance for any assistance.
open (MYFILE, '>>data.txt');
print MYFILE "Title\n";
close (MYFILE)
perl -pi -e 'print "Title\n" if $. == 1' data.text
There is a much simpler one-liner to prepend a block of text to every file. Let's say you have a set of files named body1, body2, body3, etc, to which you want to prepend a block of text contained in a file called header:
cat header | perl -0 -i -pe 'BEGIN {$h = <STDIN>}; print $h' body*
Your syntax is slightly off deprecated (thanks, Seth):
open(MYFILE, '>>', "data.txt") or die $!;
You will have to make a full pass through the file and write out the desired data before the existing file contents:
open my $in, '<', $file or die "Can't read old file: $!";
open my $out, '>', "$file.new" or die "Can't write new file: $!";
print $out "# Add this line to the top\n"; # <--- HERE'S THE MAGIC
while( <$in> ) {
print $out $_;
}
close $out;
close $in;
unlink($file);
rename("$file.new", $file);
(gratuitously stolen from the Perl FAQ, then modified)
This will process the file line-by-line so that on large files you don't chew up a ton of memory. But, it's not exactly fast.
Hope that helps.
Appending to the top is normally called prepending.
open(M,"<","data.txt");
@m = <M>;
close(M);
open(M,">","data.txt");
print M "foo\n";
print M @m;
close(M);
Alternately open data.txt- for writing and then move data.txt- to data.txt after the close, which has the benefit of being atomic so interruptions cannot leave the data.txt file truncated.
