How to search and replace string in a file in Perl - perl

Question

The content of my input file is shown below:
abc\**def\ghi**\abc\!!!!!
abc\**4nfiug\frgrefd\gtefe\wf4fs**\abc\df3gwddw
abc\**eg4/refw**\abc\f3
I need to replace whatever string in between abc \ --------------\abc in my input file with ABC\CBA.
I have tried something like below to get the strings that need to be replaced. But I get stuck when I need to use the search and replace:
my $string1 = qr/abc\W+([^a]+)/;
my $string2 = map{/$string1/ => " "} #input_file; # The string that needs to be replaced
my $string3 = 'ABC\CBA' # String in that. I want it to replace to
s/$string2/$string3/g
How can I fix this?

Answer 1

perl -i -pe 's/this/that/g;' file1

Answer 2

A one-liner to fix a file:
perl -plwe 's/abc\\\K.*(?=\\abc)/ABC\\CBA/' input.txt > output.txt
Or as a script:
use strict;
use warnings;
while (<DATA>) {
s/abc\\\K.*(?=\\abc)/ABC\\CBA/;
print;
}
__DATA__
abc\**def\ghi**\abc\!!!!!
abc\**4nfiug\frgrefd\gtefe\wf4fs**\abc\df3gwddw
abc\**eg4/refw**\abc\f3
The \K (keep) escape sequence means these characters will not be removed. Similarly, the look-ahead assertion (?= ... ) will keep that part of the match. I assumed you only wanted to change the characters in between.
Instead of \K one can use a look-behind assertion: (?<=abc\\). As a personal preference, I used \K instead.

Answer 3

#!/usr/bin/perl
use strict;
use warnings;
open my $fh,"<", "tryit.txt" or die $!;
while (my $line = <$fh>) {
$line =~ s/(abc\\)(.*?)(\\abc)/$1ABC\\CBA$3/;
print $line;
}
gives the following with the input data.
abc\ABC\CBA\abc\!!!!!
abc\ABC\CBA\abc\df3gwddw
abc\ABC\CBA\abc\f3

Answer 4

If you do not want the substitution to operate on the default variable $_, you have to use the =~ operator:
#!/usr/bin/perl
use warnings;
use strict;
my #input_file = split /\n/, <<'__EOF__';
abc\**def\ghi**\abc\!!!!!
abc\**4nfiug\frgrefd\gtefe\wf4fs**\abc\df3gwddw
abc\**eg4/refw**\abc\f3
__EOF__
my $pattern = qr/abc\\.*\\abc/; # pattern to be matched
my $string2 = join "\n", #input_file; # the string that need to be replaced
my $string3 = 'ABC\CBA'; # string i that i want it to replace to
$string2 =~ s/$pattern/$string3/g;
print $string2;

Answer 5

To address your comment about replacing text "inplace" in the file directly, you can use the -i switch for a one-liner. In a script, you can perhaps look at using Tie::File, which allows read-write access to lines of a file as (mutable) elements in an array. To copy Mike/TLP's answer:
#!/usr/bin/perl
use strict;
use warnings;
use Tie::File;
tie my #file, "Tie::File", "tryit.txt" or die $!;
# I think you have to use $_ here (done implicitly)
while (#file) {
s/(abc\\)(.*?)(\\abc)/$1ABC\\CBA$3/;
print;
}