invocation:

   $ awk '/milk/ {print "drinking milk in this way " $2}'  file1 file2 ...

   -----------------------------------------------------------------------

   $ awk -f awk-file file1 file2 ....
   $ cat awk-file
   /milk/ {print "drinking milk in this way " $2}
   $

   -----------------------------------------------------------------------

   $ ./awk-prog file1 file2 ...
   $ ls -al awk-prog
   -rwxr-xr-x 1 klim sys 72 Nov 27 16:11 awk-prog
   $ cat awk-prog 
   #! /usr/local/bin/gawk -f
   /milk/ {print "drinking milk in this way " $2}
   $  which gawk
   /usr/local/bin/gawk
   $

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
      The following is extracted from the man page of gawk.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

body of the program
   An AWK program consists  of  a  sequence  of  pattern-action
   statements and optional function definitions.
       pattern   { action statements }
       function name(parameter list) { statements }

Patterns
    BEGIN
    END
    /regular expression/
    relational expression
    pattern && pattern
    pattern || pattern
    pattern ? pattern : pattern
    (pattern)
    ! pattern
    pattern1, pattern2

The control statements are as follows:
    if (condition) statement [ else statement ]
    while (condition) statement
    do statement while (condition)
    for (expr1; expr2; expr3) statement
    for (var in array) statement
    break
    continue
    delete array[index]
    delete array
    exit [ expression ]
    { statements }

I/O Statements
     getline var 
     getline var <file  
     command | getline [var]
     command |& getline [var]
     next 
     nextfile 
     print   
     print expr-list  

Numeric Functions
     atan2(y, x)   
     cos(expr)  
     exp(expr)
     int(expr)
     log(expr)
     rand()
     sin(expr)
     sqrt(expr)
     srand([expr])

String Functions
     asort(s [, d])
     asorti(s [, d])
     gensub(r, s, h [, t])
     gsub(r, s [, t])
     index(s, t)
     length([s])
     match(s, r [, a])
     split(s, a [, r]) 
     sprintf(fmt, expr-list)
     strtonum(str)
     sub(r, s [, t])
     substr(s, i [, n])
     tolower(str) 
     toupper(str)

VARIABLES, RECORDS AND FIELDS
     AWK variables are dynamic; they  come  into  existence  when
     they are first used. 
  Records
     Normally, records are separated by newline characters.   You
     can control how records are separated by assigning values to
     the built-in variable RS. 
  Fields
     As each input record is read, gawk splits  the  record  into
     fields,  using  the  value  of  the FS variable as the field
     separator.

     Each field in the input record  may  be  referenced  by  its
     position,  $1,  $2,  and  so  on.   $0  is the whole record.
     Fields need not be referenced by constants:
          n = 5
          print $n
     prints the fifth field in the input record.
     The variable NF is set to the total number of fields in  the
     input record.

Built-in Variables
     ARGIND 
     ARGV  
     BINMODE 
     CONVFMT
     ENVIRON 
     ERRNO  
     FIELDWIDTHS
     FILENAME  
     FNR      
     FS      
     IGNORECASE
     LINT     
     NF      
     NR     
     OFMT  
     OFS  
     ORS 
     PROCINFO 
     RS      
     RT     
     RSTART  

Arrays
     Arrays are subscripted with  an  expression  between  square
     brackets ([ and ]). 
      For example:
          i = "A"; j = "B"; k = "C"
          x[i, j, k] = "hello, world\n"
     assigns the string "hello, world\n" to the  element  of  the
     array  x  which is indexed by the string "A\034B\034C".  All
     arrays in  AWK  are  associative,  i.e.  indexed  by  string
     values.
     The special operator in may be used in an if or while state-
     ment to see if an array has an index consisting of a partic-
     ular value.
          if (val in array)
               print array[val]
     If the array has multiple subscripts, use (i, j) in array.
     The in construct may also be used in a for loop  to  iterate
     over all the elements of an array.


EXAMPLES
     Print and sort the login names of all users:

          BEGIN     { FS = ":" }
               { print $1 | "sort" }

     Count lines in a file:

               { nlines++ }
          END  { print nlines }

     Precede each line by its number in the file:

          { print FNR, $0 }

     Concatenate and line number (a variation on a theme):

          { print NR, $0 }
     Run an external command for particular lines of data:

          tail -f access_log |
          awk '/myhome.html/ { system("nmap " $1 ">> logdir/myhome.html") }'