our $password = 'mysecret';

....

system( "command -p $password" );

...
## If you print $password here, you get "mysecret";
## But for the first time it was FETCH'd ONLY, 
## it would be different.
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Right, so I print the password before the system call, and then I get the real password. What are you gonna do? Go and change the password? This won't work at all.