use strict;
my $str = 'text curl -u scl_test_mon:ypB7HuW9u5yB\'_\'https://mycompany.com/api/healthcheck\'?_2>&1
text curl -u a12345:ypB7HuW9u5yB\'_\'https://mycompany.com/api/healthcheck\'?_2>&1';
my $regex = qr/(a\d+|A\d+|scl[^:]+):([^\']+)(\'|_)/p;
my $subst = '\\1:xxxxx\\3';
my $result = $str =~ s/$regex/$subst/rg;
print "The result of the substitution is' $result\n";
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html