extract multiple substr and match & replace using perl - perl

Question

I need to extract multiple substrings at fixed positions from a line and the same time replace whitespaces at another position.
For example, I have a string '01234567890 '. I want to extract characters at positions 1,2,6,7,8 and the same time if position 12, 13 are whitespaces, I want to replace them with 0101. It is all position based.
What is the best way to achieve this using perl ?
I can use substr and string comparison and then concatenate them together, but the code looked rather chuncky....

Answer 1

I would probably split (or: explode) the string into an array of single chars:
my #chars = split //, $string; # // is special with split
Now we can do array slices: extracting multiple arguments at once.
use List::MoreUtils qw(all);
if (all {/\s/} #chars[12, 13]) {
#chars[12, 13] = (0, 1);
my #extracted_chars = #chars[1, 2, 6..8];
# do something with extracted data.
}
We can then turn the #chars back into a string like
$string = join "", #chars;
If you want to remove certain chars instead of extracting them, you would have to use slices inside a loop, an ugly undertaking.
Complete sub with nice interface to do this kind of thing
sub extract (%) {
my ($at, $ws, $ref) = #{{#_}}{qw(at if_whitespace from)};
$ws //= [];
my #chars = split //, $$ref;
if (all {/\s/} #chars[#$ws]) {
#chars[#$ws] = (0, 1) x int(#$ws / 2 + 1);
$$ref = join "", #chars;
return #chars[#$at];
}
return +();
}
my $string = "0123456789ab \tef";
my #extracted = extract from => \$string, at => [1,2,6..8], if_whitespace => [12, 13];
say "#extracted";
say $string;
Output:
1 2 6 7 8
0123456789ab01ef

Answer 2

This is two separate operations, and should be coded as such. This code seems to do what you need.
use strict;
use warnings;
my $str = 'abcdefghijab efghij';
my #extracted = map { substr $str, $_, 1 } 1, 2, 6, 7, 8;
print "#extracted\n";
for (substr $str, 12, 2) {
$_ = '01' if $_ eq ' ';
}
print $str, "\n";
output
b c g h i
abcdefghijab01efghij