Regex works in terminal but not in Perl script - regex

Question

This is related to this question
Where combination of all lines that end with a backslash character is done. The following Perl command works in terminal but not in Perl script:
perl -i -p -e 's/\\\n//' input_file
In Perl script, I set it this way but it does not work:
`perl -i -p -e 's/\\\n//' $input_file_path_variable`;
**Updated the file content and code used
Input file content as follows:
foo bar \
bash \
baz
dude \
happy
Desired output content:
foo bar bash baz
dude happy
Current script:
#!/usr/bin/env perl
use Getopt::Long;
use FindBin;
use File::Path;
use File::Copy;
use DirHandle;
use FileHandle;
use File::Basename;
use Env;
use File::Slurp;
my $dummy_file = "/wdir/dummy.txt";
my $file_content = read_file($dummy_file);
print "$file_content\n";
print "==============================================\n"
my $ttest = $file_content =~ s/\\\n//;
print "$ttest\n";
Current Output
foo bar \
bash \
baz
dude \
happy
==============================================
1

Answer 1

I think I realized what your problem is. You need to make your substitution match multiple times.
You are working with this one-liner:
perl -i -p -e 's/\\\n//' input_file
Which will replace the backslash and newline once per line in a file read in line-by-line mode. And now you are trying to implement it inside another program, where you are slurping a whole file into a variable, as mentioned in your comment on another answer:
I tried reading the whole file into a variable and applied your solution, not working for me: my $file_content = read_file($input_file_path_variable) and then $file_content =~ s/\\n//;
This will only replace one time. The first match in the file. You need to add the modifier /g to make the match global, as many times as possible:
$file_content =~ s/\\\n//g;
I am not sure how you are using your code, since you are not showing us. This makes answering simple questions hard. But if my assumptions are correct, this will fix your problem.

Answer 2

I think you've changed your code/approach at least once since originally asking the question, but based on your current code, your issue is this line:
my $ttest = $file_content =~ s/\\\n//;
Firstly, the s/// operator needs a g at the end so that it's a global search and replace, instead of stopping after the first substitution.
Secondly, $file_content =~ s/\\\n// doesn't return the final string; it modifies the string in-place. (So it's changing $file_content.) In recent versions of Perl, you can add an r modifier to the end to get it to return the modified string.
So either of these will work for you:
my $ttest = ( $file_content =~ s/\\\n//gr );
Or:
( my $ttest = $file_content ) =~ s/\\\n//g;
Full script which produces the output you want:
#!/usr/bin/env perl
use strict;
use warnings;
use File::Slurp;
my $file_content = read_file('/tmp/dummy.txt');
(my $ttest = $file_content) =~ s/\\\n//g;
print "$file_content\n";
print "==============================================\n";
print "$ttest\n";

Answer 3

In a Perl you should write:
$input_file_variable =~ s/\\\n//;