editing files inline, searching for \n\n\n
Hi,
I have got two versions of a script to eliminate single line-feeds from
a file. The first one does weird stuff - duplicating lines and messing
the text file up. The second one works (I copied it from a Perl guide),
but I don't understand why. I would much prefer the first one to work -
Can you tell me how to change the first one to make it work?
Also, I understand that the <> operator reads in one line at a time. If
I wish to eliminate only triple line-feeds (\n\n\n) and leave double and
single linefeeds, I presume <> won't work. Without reading in the whole
file at once, how can I achieve this?
I am using MacPerl.
Thanks for any help!
Tim
----------------------------------------------------
Version #1 (works dreadfully....stuffs up the file)
#! perl -w -i
$filetobechanged = "iBook HD:Desktop Folder:tim.txt";
open(FILE, "+< $filetobechanged") ;
while (<FILE>) {
s/\n//g;
print FILE ;
}
close(FILE);
Version #2 (works fine)
$filetobechanged = "iBook HD:Desktop Folder:tim.txt";
@ARGV = ($filetobechanged);
$^I = ".bak";
while (<>) {
s/\n//g;;
print;
}
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0 |
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tduke
5/10/2004 4:20:11 AM
perl.beginners
29388 articles. 
4 followers.
2 Replies
659 Views
Timothy Duke <tduke@itconnect.net.au> wrote:
:
: Also, I understand that the <> operator reads in one
: line at a time. If I wish to eliminate only triple
: line-feeds (\n\n\n) and leave double and single
: linefeeds, I presume <> won't work. Without reading
: in the whole file at once, how can I achieve this?
The diamond operator uses the record separator ($/)
to determine what a line ending looks like. By setting
this to "\n\n\n" we get "lines" that have "\n\n\n" at
the end. Conveniently, 'chomp' also uses $/ to figure
out what needs to be lopped off a line.
It is best to limit a change in $/. The 'local'
function does this in a code block.
{
local $/ = "\n\n\n";
while ( <DATA> ) {
chomp;
print;
}
}
# $/ back to its old value
__END__
foo
foo
foo
foo
HTH,
Prints:
foo
foo foo
foo
HTH,
Charles K. Clarkson
--
Mobile Homes Specialist
254 968-8328
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cclarkson
5/10/2004 11:12:20 AM
Timothy Duke wrote:
>
> Hi,
Hello,
> I have got two versions of a script to eliminate single line-feeds from
> a file.
You should use chomp() to remove newlines. Using the substitution
operator globally is forcing the whole line to be scanned.
> The first one does weird stuff - duplicating lines and messing
> the text file up.
That is because you are using '+<', the read/write mode.
> The second one works (I copied it from a Perl guide),
> but I don't understand why.
That is because Perl's <> operator and the $^I variable do all the work
behind the scenes of managing your file and the backup file.
> I would much prefer the first one to work -
> Can you tell me how to change the first one to make it work?
Yes.
> Also, I understand that the <> operator reads in one line at a time.
It opens one "line" at a time where a "line" is defined by the value of
the input record separator ($/) which is set to "\n" by default.
> If
> I wish to eliminate only triple line-feeds (\n\n\n) and leave double and
> single linefeeds, I presume <> won't work. Without reading in the whole
> file at once, how can I achieve this?
Set the input record separator to paragraph mode.
> ----------------------------------------------------
>
> Version #1 (works dreadfully....stuffs up the file)
>
> #! perl -w -i
> $filetobechanged = "iBook HD:Desktop Folder:tim.txt";
> open(FILE, "+< $filetobechanged") ;
You should *ALWAYS* verify that the file opened correctly.
> while (<FILE>) {
> s/\n//g;
> print FILE ;
In read/write mode you read line one and then print over line two and
then read line three and then print over line four, etc.
> }
> close(FILE);
>
> Version #2 (works fine)
> $filetobechanged = "iBook HD:Desktop Folder:tim.txt";
> @ARGV = ($filetobechanged);
> $^I = ".bak";
> while (<>) {
> s/\n//g;;
> print;
> }
If I understand correctly, you can achieve what you want like this:
#! perl -w
use strict;
( $/, $^I, @ARGV ) = ( '', '.bak', 'iBook HD:Desktop Folder:tim.txt' );
print while <>;
However, since you seem to want to open the files yourself, you could do
it like this:
#! perl -w
use strict;
my $filetobechanged = 'iBook HD:Desktop Folder:tim.txt';
my $backup_file = "$filetobechanged.bak";
rename $filetobechanged, $backup_file
or die "Cannot rename $filetobechanged, $backup_file: $!";
open BACK, '<', $backup_file or die "Cannot open $backup_file: $!";
open FILE, '>', $filetobechanged or die "Cannot open $filetobechanged:
$!";
$/ = ''; # Set paragraph mode
while ( <BACK> ) {
print FILE;
}
close BACK;
close FILE;
__END__
John
--
use Perl;
program
fulfillment
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krahnj
5/10/2004 12:09:39 PM
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