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gawk: Return Statement

 9.2.4 The 'return' Statement
 As seen in several earlier examples, the body of a user-defined function
 can contain a 'return' statement.  This statement returns control to the
 calling part of the 'awk' program.  It can also be used to return a
 value for use in the rest of the 'awk' program.  It looks like this:
      'return' [EXPRESSION]
    The EXPRESSION part is optional.  Due most likely to an oversight,
 POSIX does not define what the return value is if you omit the
 EXPRESSION.  Technically speaking, this makes the returned value
 undefined, and therefore, unpredictable.  In practice, though, all
 versions of 'awk' simply return the null string, which acts like zero if
 used in a numeric context.
    A 'return' statement without an EXPRESSION is assumed at the end of
 every function definition.  So, if control reaches the end of the
 function body, then technically the function returns an unpredictable
 value.  In practice, it returns the empty string.  'awk' does _not_ warn
 you if you use the return value of such a function.
    Sometimes, you want to write a function for what it does, not for
 what it returns.  Such a function corresponds to a 'void' function in C,
 C++, or Java, or to a 'procedure' in Ada.  Thus, it may be appropriate
 to not return any value; simply bear in mind that you should not be
 using the return value of such a function.
    The following is an example of a user-defined function that returns a
 value for the largest number among the elements of an array:
      function maxelt(vec,   i, ret)
           for (i in vec) {
                if (ret == "" || vec[i] > ret)
                     ret = vec[i]
           return ret
 You call 'maxelt()' with one argument, which is an array name.  The
 local variables 'i' and 'ret' are not intended to be arguments; there is
 nothing to stop you from passing more than one argument to 'maxelt()'
 but the results would be strange.  The extra space before 'i' in the
 function parameter list indicates that 'i' and 'ret' are local
 variables.  You should follow this convention when defining functions.
    The following program uses the 'maxelt()' function.  It loads an
 array, calls 'maxelt()', and then reports the maximum number in that
      function maxelt(vec,   i, ret)
           for (i in vec) {
                if (ret == "" || vec[i] > ret)
                     ret = vec[i]
           return ret
      # Load all fields of each record into nums.
           for(i = 1; i <= NF; i++)
                nums[NR, i] = $i
      END {
           print maxelt(nums)
    Given the following input:
       1 5 23 8 16
      44 3 5 2 8 26
      256 291 1396 2962 100
      -6 467 998 1101
      99385 11 0 225
 the program reports (predictably) that 99,385 is the largest value in
 the array.
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