If no -f option is specified, the first operand to awk shall be the text of the awk program. The
application shall supply the program operand as a single argument to awk. If the text does not end
in a <newline>, awk shall interpret the text as if it did.
Either of the following two types of argument can be intermixed:
A pathname of a file that contains the input to be read, which is matched against the set of
patterns in the program. If no file operands are specified, or if a file operand is '-' , the
standard input shall be used.
An operand that begins with an underscore or alphabetic character from the portable character set
(see the table in the Base Definitions volume of IEEE Std 1003.1-2001, Section 6.1, Portable
Character Set), followed by a sequence of underscores, digits, and alphabetics from the portable
character set, followed by the '=' character, shall specify a variable assignment rather than a
pathname. The characters before the '=' represent the name of an awk variable; if that name is an
awk reserved word (see Grammar ) the behavior is undefined. The characters following the equal
sign shall be interpreted as if they appeared in the awk program preceded and followed by a
double-quote ( ' )' character, as a STRING token (see Grammar ), except that if the last character
is an unescaped backslash, it shall be interpreted as a literal backslash rather than as the first
character of the sequence "\"" . The variable shall be assigned the value of that STRING token
and, if appropriate, shall be considered a numeric string (see Expressions in awk ), the variable
shall also be assigned its numeric value. Each such variable assignment shall occur just prior to
the processing of the following file, if any. Thus, an assignment before the first file argument
shall be executed after the BEGIN actions (if any), while an assignment after the last file
argument shall occur before the END actions (if any). If there are no file arguments, assignments
shall be executed before processing the standard input.