use strict;
my $str = '\\int_{1}^{2}\\frac{x}{x/2}+{\\frac{\\sqrt{81}}{7x}}^7
\\int x
\\int_{19{} cz }^{2}{\\frac{x}{x/2}+7}+7
(\\int_{1}^{2}\\frac{x}{x/2})/2';
my $regex = qr/\{((?>[^{}]+|{(?1)})*)\}/mp;
my $subst = '$1';
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