parsing of text files using perl

[kkazakos]

Hello friends,

I am exploring write now the PERL language and i must say that i am very excited!!!!

My first personal goal is to write a simple program in perl that does the following :

It reads the info from file1.txt. File1 structure is:
r 250 4 26 960 0 0 88 x1*
There are 64000lines that have the above format with x1....x64000.

I would like to take all the x1..x64000 ONLY and to print them in a new file which i named file2.txt.

Therefore file2.txt will have only the x1...x64000.

Could u please guide me on how to do that?
I have serious problems since i do not know how to recognize the end of each line...

regards
kostas

 

[stevexff]

use strict;
use warnings;

while (<>) {                       # read each line
   my $x64k = (split /\s+/) [-1];  # split and take last item
   print $x64k;                    # print it out
}                                  # er, that's it...

As you are new at this, I've kept it simple. No file opening or closing; it's all implicit. To use it just

perl myscript.pl myinputfile.txt > myoutputfile.txt

Steve

[small]"Every program can be reduced by one instruction, and every program has at least one bug. Therefore, any program can be reduced to one instruction which doesn't work." (Object:erlDesignPatterns)[/small]

 

[kkazakos]

Hello stevexff,

Thanks. Could you please take a look at the following code and let me know if it is correct? Is this how a PERL program should be constructed?
------------------------------------------------------------
#!/usr/local/bin/perl

$file = 'C:\telemetry_vld.txt';
open(INFO, $file); #opens file telemetry_vld.txt
open(DATA, ">final.txt"); #file to write data to
@lines = <INFO>; #assigns lines to array

while (<>) #go through each line in file
{
my $x64k = (split /\s+/) [-1]; # split and take last item
DATA == $x64k;
print DATA "\n";
}

close(INFO); #closes file
close(DATA);
------------------------------------------------------------

What if i had only 4 lines? Then what will have happened?

regards
kkazakos

 

[kkazakos]

Also i would like to get rid of the '*' character

What i mean is this:
I have the input file e.g. ==>
r 250 4 26 960 0 0 88 x1*
r 250 5 26 356 0 0 56 x2*

I want in the output file ==>
x1
x2


How do i do this?

thanks

 

[travs69]

DATA ==  $x64k;
  print DATA "\n";

should be

 print DATA "$x64k\n";

 

[travs69]

Get rid of the *

$x64k =~ s/\*//g;

but I'm sure someone has a better idea

 

[kkazakos]

$x64k =~ s/\*//g;

i am sorry but you lost me there..

where in the code shall i put that?

thank you
kkazakos

 

[KevinADC]

borrowing heavily from steves code:

[gray]#!/usr/local/bin/perl[/gray]
[url=http://perldoc.perl.org/functions/use.html][black][b]use[/b][/black][/url] [green]strict[/green][red];[/red]
[black][b]use[/b][/black] [green]warnings[/green][red];[/red]


[url=http://perldoc.perl.org/functions/my.html][black][b]my[/b][/black][/url] [blue]$file[/blue] = [red]'[/red][purple]C:/telemetry_vld.txt[/purple][red]'[/red][red];[/red]
[url=http://perldoc.perl.org/functions/open.html][black][b]open[/b][/black][/url][red]([/red]IN, [blue]$file[/blue][red])[/red][red];[/red]         [gray][i]#opens file telemetry_vld.txt[/i][/gray]
[black][b]open[/b][/black][red]([/red]OUT, [red]"[/red][purple]>final.txt[/purple][red]"[/red][red])[/red][red];[/red] [gray][i]#file to write data to[/i][/gray]
[olive][b]while[/b][/olive] [red]([/red]<IN>[red])[/red]             [gray][i]#go through each line in file[/i][/gray]
[red]{[/red]
  [black][b]my[/b][/black] [blue]$x[/blue] = [red]([/red][url=http://perldoc.perl.org/functions/split.html][black][b]split[/b][/black][/url] [red]/[/red][purple][purple][b]\s[/b][/purple]+[/purple][red]/[/red][red])[/red] [red][[/red]-[fuchsia]1[/fuchsia][red]][/red][red];[/red]  [gray][i]# split and take last item[/i][/gray]
  [blue]$x[/blue] =~ [red]tr/[/red][purple]*[/purple][red]/[/red][purple][/purple][red]/[/red][red]d[/red][red];[/red] [gray][i]#remove * from string[/i][/gray]
  [url=http://perldoc.perl.org/functions/print.html][black][b]print[/b][/black][/url] OUT [red]"[/red][purple][blue]$x[/blue][purple][b]\n[/b][/purple][/purple][red]"[/red][red];[/red]
[red]}[/red]

[url=http://perldoc.perl.org/functions/close.html][black][b]close[/b][/black][/url][red]([/red]IN[red])[/red][red];[/red]
[black][b]close[/b][/black][red]([/red]OUT[red])[/red][red];[/red]

[tt]------------------------------------------------------------
Pragmas (perl 5.8.8) used :
[ul]
[li]strict - Perl pragma to restrict unsafe constructs[/li]
[li]warnings - Perl pragma to control optional warnings[/li]
[/ul]
[/tt]

------------------------------------------
- Kevin, perl coder unexceptional!

 

[stevexff]

$x64k =~ s/\*//g;

i am sorry but you lost me there..

Understandable, if you are new to Perl. This is a Regular Expression and is one of the most powerful features of Perl, but unfortunately one of the most cryptic.

In English, it says "look at the contents of variable $x64k, and replace every occurrence of "*" with "". This effectively removes your trailing *, although technically we should say

$x64k =~ s/\*$//;

which tells it to only replace the * if it is the last character.

There's a little bit of RegEx in my split command, too. The /\s+/ says "split on one or more whitespace characters.

Now's probably not the time, but there is more information in the perlre documentation. There's also a very good RegEx site at

http://www.regular-expressions.info

Steve

[small]"Every program can be reduced by one instruction, and every program has at least one bug. Therefore, any program can be reduced to one instruction which doesn't work." (Object:erlDesignPatterns)[/small]