#!/usr/bin/perl

use warnings;
use strict;

$\ = $/;

$_ = reverse "(a+b)*c"; # or some longer sequence

s/\)([^()]+)\(/]$1[/g;

print scalar reverse y/][/)(/r;

__END__

$ perl test.pl
Missing right curly or square bracket at test.pl line 10, within string
syntax error at test.pl line 10, at EOF
Execution of test.pl aborted due to compilation errors.

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;
use feature 'say';

my $reversed = reverse "(a+b)*c"; # or some longer sequence
$reversed =~ tr/()/[]/;
my $str = reverse $reversed;
say $str;

__END__

$ perl test.pl
[a+b]*c

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;
use feature 'say';

my $test = "(a+b)*c";
$test =~ tr/()/[]/;
say $test;

__END__

$ perl test.pl
[a+b]*c

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;
use feature 'say';

sub replaceChar {
    my ($str, $char, $replace) = @_;
    substr($str, index($str, $char), length($char), $replace);
    return $str;
}

my $s = "(a+b)*c";
my $leftParenthesis = "(";
my $rightParenthesis = ")";
my $leftCurlyBracket = "[";
my $rightCurlyBracket = "]";

my $str = replaceChar($s, $leftParenthesis, $leftCurlyBracket);
say $str;
say replaceChar($str, $rightParenthesis, $rightCurlyBracket);

__END__

$ perl test.pl
[a+b)*c
[a+b]*c