use strict;
my $str = '2019-05-14 11:28:08,257 [tomcat-http--12] INFO com.my.org.SomeClass - Usage Event: ,SomeField=null,SomeOtherField=Some value,Action=[Name] Action Detail,OtherField=null';
my $regex = qr/(Action=)(\[[^,]+)/mp;
my $subst = '';
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