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`perror'--print an error message on standard error

     #include <stdio.h>
     void perror(char *PREFIX);
     void _perror_r(void *REENT, char *PREFIX);
Use `perror' to print (on standard error) an error message
corresponding to the current value of the global variable `errno'.
Unless you use `NULL' as the value of the argument PREFIX, the error
message will begin with the string at PREFIX, followed by a colon and a
space (`: '). The remainder of the error message is one of the strings
described for `strerror'.
   The alternate function `_perror_r' is a reentrant version.  The
extra argument REENT is a pointer to a reentrancy structure.
`perror' returns no result.
ANSI C requires `perror', but the strings issued vary from one
implementation to another.
   Supporting OS subroutines required: `close', `fstat', `isatty',
`lseek', `read', `sbrk', `write'.