File: gawk.info,  Node: Variable Scope,  Next: Pass By Value/Reference,  Prev: Calling A Function,  Up: Function Calling

9.2.3.2 Controlling Variable Scope
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Unlike in many languages, there is no way to make a variable local to a
'{' ... '}' block in 'awk', but you can make a variable local to a
function.  It is good practice to do so whenever a variable is needed
only in that function.

   To make a variable local to a function, simply declare the variable
as an argument after the actual function arguments (*note Definition
Syntax::).  Look at the following example, where variable 'i' is a
global variable used by both functions 'foo()' and 'bar()':

     function bar()
     {
         for (i = 0; i < 3; i++)
             print "bar's i=" i
     }

     function foo(j)
     {
         i = j + 1
         print "foo's i=" i
         bar()
         print "foo's i=" i
     }

     BEGIN {
           i = 10
           print "top's i=" i
           foo(0)
           print "top's i=" i
     }

   Running this script produces the following, because the 'i' in
functions 'foo()' and 'bar()' and at the top level refer to the same
variable instance:

     top's i=10
     foo's i=1
     bar's i=0
     bar's i=1
     bar's i=2
     foo's i=3
     top's i=3

   If you want 'i' to be local to both 'foo()' and 'bar()', do as
follows (the extra space before 'i' is a coding convention to indicate
that 'i' is a local variable, not an argument):

     function bar(    i)
     {
         for (i = 0; i < 3; i++)
             print "bar's i=" i
     }

     function foo(j,    i)
     {
         i = j + 1
         print "foo's i=" i
         bar()
         print "foo's i=" i
     }

     BEGIN {
           i = 10
           print "top's i=" i
           foo(0)
           print "top's i=" i
     }

   Running the corrected script produces the following:

     top's i=10
     foo's i=1
     bar's i=0
     bar's i=1
     bar's i=2
     foo's i=1
     top's i=10

   Besides scalar values (strings and numbers), you may also have local
arrays.  By using a parameter name as an array, 'awk' treats it as an
array, and it is local to the function.  In addition, recursive calls
create new arrays.  Consider this example:

     function some_func(p1,      a)
     {
         if (p1++ > 3)
             return

         a[p1] = p1

         some_func(p1)

         printf("At level %d, index %d %s found in a\n",
              p1, (p1 - 1), (p1 - 1) in a ? "is" : "is not")
         printf("At level %d, index %d %s found in a\n",
              p1, p1, p1 in a ? "is" : "is not")
         print ""
     }

     BEGIN {
         some_func(1)
     }

   When run, this program produces the following output:

     At level 4, index 3 is not found in a
     At level 4, index 4 is found in a

     At level 3, index 2 is not found in a
     At level 3, index 3 is found in a

     At level 2, index 1 is not found in a
     At level 2, index 2 is found in a