adding text in a file PERL

[goude]

Hello everyone,

I was wondering if someone can help me. I am trying to insert a textline in a file, but I want to insert it on a particular line number without replacing the text that is already there.
The text I want to insert is Option "TwinView" "True" on line 7 and I want to insert it to the xorg file below.

1) Section "Screen"
2) Identifier "Screen1"
3) Device "Videocard1"
4) Monitor "Monitor1"
5) DefaultDepth 24
6) Option "MetaModes" "nvidia-auto-select, nvidia-auto-select"
7) SubSection "Display"
8 ) Viewport 0 0
9) Depth 24
10)Modes "1280x1024"
11)EndSubSection
12) EndSection

The script I've written so far after reading a not very useful book called perl in 24 hours is below.


$newline= 'This goes into text';
open(FILE, ">>/home/yanni/scripts/testfiles/j_run") or die "Can't open file: $!\n";
@textlines = <FILE>;
while(<FILE>)
{
if { print FILE "$newline\n"; }
else {print;}
}
close(FILE);

First, I assign the text into a variable, then open the file for appending.
Put the content of that file into an array and read it with a while command. My problem is that I don't know how to say to perl "after reading line 6, stop and print at line 7 without overwriting what's on that line". In the book it mentions the $_ variable, which confused me but i think that's what I need to use but I don't know how.

Any suggestions please?

Thanks a lot.

[drl]

Hi.

Like Kirk, I change the problem. If learning perl is your goal, then we can talk about that, but I would use the stream editor sed for this:

#!/usr/bin/env bash

# @(#) s1       Demonstrate append text to specific line with sed.

echo
set +o nounset
LC_ALL=C ; LANG=C ; export LC_ALL LANG
echo "Environment: LC_ALL = $LC_ALL, LANG = $LANG"
echo "(Versions displayed with local utility \"version\")"
version >/dev/null 2>&1 && version "=o" $(_eat $0 $1) sed
set -o nounset
echo

FILE=${1-data1}

echo " Data file $FILE:"
cat $FILE

echo
echo " Results:"
sed '/SubSection "Display"/s/$/ Option "TwinView" "True"/' $FILE

exit 0

Producing:

% ./s1

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 2.6.11-x1, i686
Distribution        : Xandros Desktop 3.0.3 Business
GNU bash 2.05b.0
GNU sed version 4.1.2

 Data file data1:
1) Section "Screen"
2) Identifier "Screen1"
3) Device "Videocard1"
4) Monitor "Monitor1"
5) DefaultDepth 24
6) Option "MetaModes" "nvidia-auto-select, nvidia-auto-select"
7) SubSection "Display"
8 ) Viewport 0 0
9) Depth 24
10)Modes "1280x1024"
11)EndSubSection
12) EndSection

 Results:
1) Section "Screen"
2) Identifier "Screen1"
3) Device "Videocard1"
4) Monitor "Monitor1"
5) DefaultDepth 24
6) Option "MetaModes" "nvidia-auto-select, nvidia-auto-select"
7) SubSection "Display" Option "TwinView" "True"
8 ) Viewport 0 0
9) Depth 24
10)Modes "1280x1024"
11)EndSubSection
12) EndSection

I think sed can be cryptic, but it's probably easier than learning an entire new language like perl ... cheers, drl

[goude]

Thanks a lot for your reply drl but I'd rather use Perl.
I need to write a statement after if that says when you read line 7 print "something" below that line.

What I have done so far is here:

open(FILE, "+>>/home/yanni/scripts/testfiles/j_run") || die "Can't open file: $!\n";
@textlines = <FILE>; 
 while(<FILE>)
   {
       if  (@textlines: $textlines[7] { print FILE "something\n"; }
       else {print;}
   }
close(FILE);

With @textlines = <FILE>; the contents of the file are read into an array (according to the book), with while perl reads the file line by line and then I'm trying to say that when you read element 7 of the array which I think is line 7 (plz, correct me if I'm wrong) print "something".

[drl]

Hi.

OK, perl it is. In your situation, there are two basic ways of getting to the line of interest. One is by matching unique content, as we did with sed. The second is by counting lines -- because you know the number of the line. Neither method requires all lines to be in memory, because we either match or count a single line as we read. Therefore, we do not need to use an array. If the current line is of interest, we modify it, and in any case, we print it. First case:

#!/usr/bin/perl

# @(#) p1       Demonstrate append text to a specific line, matching.

use warnings;
use strict;

my ($debug);
$debug = 0;
$debug = 1;

while (<>) {
  chomp;
  if (/SubSection "Display"/) {
    s/$/ Option "TwinView" "True"/;
  }
  print "$_\n";
}

print STDERR " ( Lines read: $. )\n";

exit(0);

Producing:

% ./p1 data1
1) Section "Screen"
2) Identifier "Screen1"
3) Device "Videocard1"
4) Monitor "Monitor1"
5) DefaultDepth 24
6) Option "MetaModes" "nvidia-auto-select, nvidia-auto-select"
7) SubSection "Display" Option "TwinView" "True"
8 ) Viewport 0 0
9) Depth 24
10)Modes "1280x1024"
11)EndSubSection
12) EndSection
 ( Lines read: 12 )

Second:

#!/usr/bin/perl

# @(#) p2       Demonstrate append text to a specific line, counting.

use warnings;
use strict;

my ($debug);
$debug = 0;
$debug = 1;

while (<>) {
  chomp;
  if ( $. == 7 ) {
    s/$/ Option "TwinView" "True"/;
  }
  print "$_\n";
}

print STDERR " ( Lines read: $. )\n";

exit(0);

Also producing:

% ./p2 data1
1) Section "Screen"
2) Identifier "Screen1"
3) Device "Videocard1"
4) Monitor "Monitor1"
5) DefaultDepth 24
6) Option "MetaModes" "nvidia-auto-select, nvidia-auto-select"
7) SubSection "Display" Option "TwinView" "True"
8 ) Viewport 0 0
9) Depth 24
10)Modes "1280x1024"
11)EndSubSection
12) EndSection
 ( Lines read: 12 )

You may have noticed that the substitution is exactly the same as in sed, but we are using a lot more characters to do the same thing. That's why I would use sed.

See perldoc perldoc for how to find documentation on perl constructs ... cheers, drl

[goude]

Thank you very much for your help drl.
I have a better understanding on how

[goude]

Thank you very much for your help drl.
I now have a better understanding on how I can do this (i.e. appending text files), however there is something else.
On your second script you state if $. is 7 do "that".
$. is not defined, how come you make an if "statement" about it?

use warnings;
use strict;

my ($debug);
$debug = 0;
$debug = 1;

while (<>) {
  chomp;
  if ( $. == 7 ) {
    s/$/ Option "TwinView" "True"/;
  }
  print "$_\n";
}

print STDERR " ( Lines read: $. )\n";

exit(0);

Also, can you please tell me why the angle operators are the only characters in your while expression? Shouldn't you include the filehandle in there? Just asking.