$a="/my/module/path";
eval "use lib '$a'";
eval { use MyModule; }
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No, that won't work. The use inside the eval BLOCK is compiled at compile time, but the string in eval EXPR is not. eval "use Foo"; is nothing but an obfuscated way to say require Foo; Foo->import;

Neither case is a job for eval here. If you want variable paths at compile time, you do the following:

my $libpath;
BEGIN { $libpath = "/foo/bar"; }
use lib $libpath;
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If you want to load modules with dynamic @INC at runtime, you make use of the aforemention construct:

{
    local @INC = ("/foo/bar", @INC);
    require Foo;
    Foo->import;
}
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eval will not help. And $a is a really awful name for a variable (plus $a and $b are reserved for sort). :)

Makeshifts last the longest.

BEGIN {
  my $a = "c:/";
  use lib "$a";
}

use GetWords;
print new GetWords;
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The warning message (without -w swicth or 'use warnings'):

Empty compile time value given to use lib at C:\Documents and Settings\mt2k\De sktop\testing.pl line 3

-------------------------------------
eval reverse@{[lreP
=>q{ tsuJ\{qq},' rehtonA'
,q{\}rekcaH },' tnirp']}[1+1+
1,1-1,1+1,1*1,(1+1)*(1+1)];
-------------------------------------

Mm?

my $somewhere;
BEGIN { $somewhere = q(/over/the/rainbow) }

use lib $somewhere;
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Makeshifts last the longest.

Oh yeah.. that's funny. Get this - right as soon as the implicit BEGIN (via the use) is parsed inside the currently-being-parsed BEGIN block it is executed. So you're attempting to use $a in your nested BEGIN block prior to defining it. See?

 BEGIN {
   my $a = "c:/";
   BEGIN { require "$a"; import "$a"; }
 }
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