A cleaned up copy of what you posted:
#!/usr/bin/perl
use strict;
use warnings;
my @cmd = ('/sbin/route');
push @cmd, 'add';
push @cmd, 'default';
push @cmd, 'gw',
push @cmd, '172.16.0.200',
push @cmd, 'dev';
push @cmd, 'enxb827eb95400d';
system(@cmd);
some lines end with commas when they should be semicolons:
#!/usr/bin/perl
use strict;
use warnings;
my @cmd = ('/sbin/route');
push @cmd, 'add';
push @cmd, 'default';
push @cmd, 'gw';
push @cmd, '172.16.0.200';
push @cmd, 'dev';
push @cmd, 'enxb827eb95400d';
system(@cmd);
If in doubt, print what your variables contain. Tutorials->PerlMonks for the Absolute Beginner/Basic debugging checklist.