Is there a reason you have to define $wget_url outside of the subroutine? If not, then this change should allow it to work as you desire:
my $testfile="/home/user/symbol_list";
&get_symbol_data($testfile);
sub get_symbol_data {
open (FILE, $_[0]) || die "Can't open $_[0] $!\n";
@sym_array = <FILE>;
close <FILE>;
foreach $symbol (@sym_array) {
chomp $symbol;
my $wget_url=qq~/home/user/sym_dir/${symbol}_2013 'http://www.downl
+oadsite.com/${symbol}.dat'~;
`usr/bin/wget -O $wget_url`;
}
}
The qq~...~ allows all occurrences of $symbol to be properly interpolated, even inside single quotes in a string assignment.