Yes, braces are one way to disambiguate where the variable name ends.
Often I will use the concatenate operator to avoid the need for braces.
This probably runs slower, but you can space out the var names to be substituted in order to make them more obvious (YMMV).

my $opstr = '01';
my $foo = "a_${opstr}_b";
my $bar = 'a_'. $opstr .'_b';

print "$foo\n";
print "$bar\n";

[download]
Also, OP probably meant: my ($opstr) = $vmstr =~ /-(\d+)$/; in the case of one digit (e.g. 0)?

In reply to Re^2: appending a variable by Marshall
in thread appending a variable by pragovnj

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