Sometimes, the IRB prints a warning during boot:
irb: warn: can't alias source from irb_source.
Explanation
During boot, the IRB creates 
  many aliases
  
    Show archive.org snapshot
  
 to give the user quick access to irb functions like source-ing a file.
However, if IRB's context already responds to the alias it wants to create Show archive.org snapshot , it will not overwrite the method with its alias and print the above warning instead.
This may happen especially when invoking IRB programmatically, e.g. in Spreewald Show archive.org snapshot .
Solution
A workaround is to 
  undef the method IRB complains about
  
    Show archive.org snapshot
  
, prior to IRB initialization.
If this is not feasible, e.g. because you depend on the method, you can try to patch IRB, e.g. by modifying the EXTEND_COMMANDS or overriding 
  this method
  
    Show archive.org snapshot
  
.