ay isn't the target of the change to %ENV which produced the warning.
Too late to run %s block
(W void) A CHECK or INIT block is being defined during run time proper, when the opportunity to run them has already passed. Perhaps you are loading a file with require or do when you should be using use instead. Or perhaps you should put the require or do inside a BEGIN block.
Unknown open() mode '%s'
(F) The second argument of 3-argument open() is not among the list of valid modes: <, >, >>, +<, +>, +>>, -|, |-.
Unknown process %x sent message to prime_env_iter: %s
(P) An error peculiar to VMS. Perl was reading values for %ENV before iterating over it, and someone else stuck a message in the stream of data Perl expected. Someone's very confused, or perhaps trying to subvert Perl's population of %ENV for nefarious purposes.
Unrecognized escape \\%c passed through
(W misc) You used a backslash-character combination which is not recognized by Perl. The character was understood literally.
Unterminated attribute parameter in attribute list
(F) The lexer saw an opening (left) parenthesis character while parsing an attribute list, but the matching closing (right) parenthesis character was not found. You may need to add (or remove) a backslash character to get your parentheses to balance. See attributes.
Unterminated attribute list
(F) The lexer found something other than a simple identifier at the start of an attribute, and it wasn't a semicolon or the start of a block. Perhaps you terminated the parameter list of the previous attribute too soon. See attributes.
Unterminated attribute parameter in subroutine attribute list
(F) The lexer saw an opening (left) parenthesis character while parsing a subroutine attribute list, but the matching closing (right) parenthesis character was not found. You may need to add (or remove) a backslash character to get your parentheses to balance.
Unterminated subroutine attribute list
(F) The lexer found something other than a simple identifier at the start of a
