perl + append text between two lines in file

Question

hi all

I need to edit file , the main issue is to append text between two known lines in the file

for example I need to append the following text

a b c d e f

1 2 3 4 5 6

bla bla

Between the first_line and the second_line

first_line=")"

second_line="NIC Hr_Nic ("

remark: first_line and second_line argument can get any line or string

How to do this by perl ? ( i write bash script and I need to insert the perl syntax in my script)

lidia

Answer 1

Well to concenate strings you do

my $text = $first_line . $second_line;

or

my $text = $first_line;
$text .= $second_line;

Answer 2

You could read the file in as a single string and then use a regular expression to do the search and replace:

use strict;
use warnings;

# Slurp file myfile.txt into a single string
open(FILE,"myfile.txt") || die "Can't open file: $!";
undef $/;
my $file = <FILE>;

# Set strings to find and insert
my $first_line = ")";
my $second_line = "NIC Hr_Nic (";
my $insert = "hello world";

# Insert our text
$file =~ s/\Q$first_line\E\n\Q$second_line\E/$first_line\n$insert\n$second_line/;

# Write output to output.txt
open(OUTPUT,">output.txt") || die "Can't open file: $!";
print OUTPUT $file;
close(OUTPUT);

By unsetting $/ we put Perl into "slurp mode" and so can easily read the whole file into $file.

We use the s/// operator to do a search and replace using our two search lines as a pattern.

The \Q and \E tell Perl to escape the strings between them, i.e. to ignore any special characters that happen to be in $first_line or $second_line.

You could always write the output over the original file if desired.

The problem as you state it is not solvable using the -i command line option since this option processes a file one line at a time; to insert text between two specific lines you'll need to know about two lines at once.

Answer 3

I'm not sure if I understand your question correctly. A "before and after" example of the file content would, I think, be easier. Anyhow, Here's my take on it, using splice instead of a regular expression. We must of course know the line numbers for this to work.

Load the file into an array:

my @lines;
open F, '<', 'filename' or die $!;
push @lines, $_ for <F>;
close F;

Insert the stuff (see perldoc -f splice):

splice @lines, 1, 0, ('stuff');

..and you're done. All you need to do now is save the array again:

open F, '>', 'filename' or die $!;
print F @lines;
close F;