as - assembler

     as [ - ] name ...

     As assembles the concatenation of the named files.  If the
     optional first argument - is used, all undefined symbols in
     the assembly are treated as global.

     The output of the assembly is left on the file a.out.  It is
     executable if no errors occurred during the assembly, and if
     there were no unresolved external references.

     /lib/as2        pass 2 of the assembler
     /tmp/atm[1-3]?  temporary
     a.out           object

     ld (I), nm (I), db (I), a.out (V), `UNIX Assembler Manual'.

     When an input file cannot be read, its name followed by a
     question mark is typed and assembly ceases.  When syntactic
     or semantic errors occur, a single-character diagnostic is
     typed out together with the line number and the file name in
     which it occurred.  Errors in pass 1 cause cancellation of
     pass 2.  The possible errors are:

     )  Parentheses error
     ]  Parentheses error
     <       String not terminated properly
     *  Indirection used illegally
     A  Error in address
     B  Branch instruction is odd or too remote
     E  Error in expression
     F  Error in local (`f' or `b') type symbol
     G  Garbage (unknown) character
     I  End of file inside an if
     M  Multiply defined symbol as label
     O  Word quantity assembled at odd address
     P  `.' different in pass 1 and 2
     R  Relocation error
     U  Undefined symbol
     X  Syntax error

     Symbol table overflow is not checked.  x errors can cause
     incorrect line numbers in following diagnostics.