Why is a variable name followed by an underscore not evaluated correctly during string interpolation in Perl?

Why is a variable name followed by an underscore not evaluated correctly during string interpolation in Perl?

my $i = 3;

print "i = $i\n"; # works, prints "i = 3"
print "_i = _$i\n"; # works, 开发者_高级运维prints "_i = _3"
print "i_ = $i_\n"; # FAILS, prints "i_ = "
print "_i_ = _$i_\n"; # sort of works, prints "_i_ = _"

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In addition to the other answers, you can use the alternative syntax for specifying variables:

print "i_ = ${i}_\n";

Note the usage of curly brackets: { and } to specify the variable name. Whenever in doubt, you may opt for this syntax.

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$i_ is a valid identifier, so it's trying to print the value of that variable (which you haven't set, so it is undef).

Turn on strict and warnings.

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Mat is right. If you really need that underscore immediately after the value use backslash: "$i\_".

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Always use these:

use strict;
use warnings;