[SOLVED] perl script to read line by line

casualzone · 08-02-2011, 05:29 AM

hi
I just learn perl script
May i know how to simplify the code below especially in the red color part?
i saw some examples in internet, they use "next" command

#!/apps/perl/bin/perl
system(clear);
open($INPUT, $ARGV[0]) || die('No input_net file');
@INPUT_FILE=<$INPUT>;
$INPUT_LINE=@INPUT_FILE;
close($INPUT);

$line=0;
while($line < $INPUT_LINE){

if(@INPUT_FILE[$line] =~ m/abcd/ )
{
do_something;
}

}

anomie · 08-02-2011, 03:30 PM

Here's a slightly different approach:

Code:

#!/usr/bin/perl

use warnings ;

$infile = "foo" ;

open(INFILE, $infile) || die "Problem opening file: $!" ;
@lines = <INFILE> ;
close INFILE ;

foreach(@lines) {

  print if /bar/ ;

}

You're using @ARGV, et al., but I'm sure you can piece main points together. Also, just want to confirm you are aware that you are sucking the entire file into memory before processing it.

(NB: I am a perl novice. There may be cleverer ways still to tackle this problem. But what I posted should be acceptable.)

markush · 08-02-2011, 03:43 PM

Code:

#!/usr/bin/perl

use warnings ;

$infile = "foo" ;

open(INFILE, $infile) || die "Problem opening file: $!" ;
@lines = <INFILE> ;


while(<INFILE>) {

  print if /bar/ ;

}
close INFILE ;

Quote:

(NB: I am a perl novice. There may be cleverer ways still to tackle this problem. But what I posted should be acceptable.)

Well, it is not necessary to store the INFILE in an array.

Markus

anomie · 08-02-2011, 03:49 PM

I agree. I thought maybe he was doing it for performance reasons (RAM access vs. disk I/O), but in looking at OP's background and the context here, that is unlikely.

markush's modification is probably best in this case.

markush · 08-02-2011, 03:55 PM

Hello anomie,

the code as I wrote it is always used in such cases in Perl-tutorials and also in the Camel-book http://oreilly.com/catalog/9780596000271

In general one can say that with Perl most often the shortest code is the most efficient. Shortcuts are not only "syntactical sugar" but are made for the efficiency.

Markus

Tinkster · 08-02-2011, 07:10 PM

Moved: This thread is more suitable in <PROGRAMMING> and has been moved accordingly to help your thread/question get the exposure it deserves.

Sergei Steshenko · 08-02-2011, 11:34 PM

Quote:

Originally Posted by casualzone

hi
I just learn perl script
...

http://perldoc.perl.org/ -> http://perldoc.perl.org/index-overview.html -> http://perldoc.perl.org/perlintro.html
http://perldoc.perl.org/perlopentut.html - this one has examples you need.

First refer to that official http://perldoc.perl.org/ site.

casualzone · 08-03-2011, 12:06 AM

thank you very much

need to spend some time to pick up this skill

casualzone · 08-03-2011, 12:23 AM

the input file is not a fixed file name eg "foo", it is an user input file that can be any file name

For this case, is it true that i got to use $ARGV[0]?

Sergei Steshenko · 08-03-2011, 12:28 AM

Quote:

Originally Posted by casualzone

the input file is not a fixed file name eg "foo", it is an user input file that can be any file name

For this case, is it true that i got to use $ARGV[0]?

Using @ARGV is a right thing to do, but do not reinvent the wheel:

Code:

http://cpan.org/ -> http://search.cpan.org/ -> http://search.cpan.org/search?query=getopt&mode=all
                                               http://search.cpan.org/search?query=...+long&mode=all

casualzone · 08-03-2011, 12:33 AM

just test the code:

#!/apps/perl/bin/perl

use warnings;
system(clear);

$infile = "ttt.txt";
open( INFILE, $infile) || die("Problem opening file: $ !");

while(<INFILE>) {
@lines = <INFILE>;
print @lines;
}
close(INFILE);

---------------
ttt.txt file
------------
hello
##############
heheheheheh
hehehehe
hehehe
hehe
he
########

-------
RESULT
-------
##############
heheheheheh
hehehehe
hehehe
hehe
he
########

WHY THE FIRST LINE IS MISSING?

casualzone · 08-03-2011, 12:44 AM

another test case:

#!/apps/perl/bin/perl
system(clear);

open( INFILE, $ARGV[0] ) || die("Can't open file for read.\n");

while (<INFILE>)
{
$line = <INFILE>;
print("-- $line");
}

close(INFILE);

-------
OUTPUT
--------
-- ##############
-- hehehehe
-- hehe
-- ########

WHY THE ODD LINES IS MISSING?

markush · 08-03-2011, 12:50 AM

Hi,

you've written much too much code

try this

Code:

#!/apps/perl/bin/perl

use strict;
use warnings;
system(clear);

my $infile = "ttt.txt";
open( INFILE, $infile) || die("Problem opening file: $ !");

while(<INFILE>) {
        @lines = <INFILE>;
        print @lines;
}
close(INFILE);

You should read the manuals in the link which Sergei Steshenko posted!

In the above code you see a typical situation in Perl. If it is clear what you mean, you don't have to say it (like in human languages). Within a loop the variable $_ stores the iterated variable, you can write "print $_;" but even this is too much because in this context it is clear that $_ is meant, so you don't have to write $_

Also note that it is important to declare a variable with the "my" keyword. It tells perl that this variable is local to this (file) package. And "use strict;" will give you hints about this, at least while learning Perl you should use it.

Markus

markush · 08-03-2011, 01:05 AM

Hi, to your above examples,

in the first case you use the complete INFILE as an array, in this case no loop is needed.

Code:

while(<INFILE>) {
       @lines = <INFILE>;
       print @lines;
}

in the second case you use the complete INFILE as a scalar value.

Code:

$line = <INFILE>

I don't even understand what this code does, but most likely it is not what you wanted to do.

Markus

Sergei Steshenko · 08-03-2011, 01:14 AM

Quote:

Originally Posted by markush

...
in the second case you use the complete INFILE as a scalar value.

Code:

$line = <INFILE>

I don't even understand what this code does, but most likely it is not what you wanted to do.

Markus

Not necessarily complete. By default just one line is read.