awk functions

awk supports functions and comes with a collection of built-in and useful functions.

User defined.

https://www.gnu.org/software/gawk/manual/html_node/User_002ddefined.html#User_002ddefined

  • function - required keyword
  • name( - required, alpha-numeric and underscore. Open parenthesis requird with no space.
  • [parm-list] - optional parameter list, comma delimited arguments.
  • ) - closing parenthesis.
  • { - open brace - start of code block.
  • actions - series of actions.
  • return argument - optional.
  • } - close brace, end of code block. 

    function name( [parm-list] )
{
  actions
  [return argument]
}


    #f.awk
#  For demo, use echo "" | awk -f f.awk
# Note that awk uses a 2 pass process, and functions
#   can be declared later in the script but are available
#   earlier in the script.
# 
# The main block of code, the driver awk script is referred to 
#   in comments as main.
#
BEGIN {
  # no space between function and (
  num=7;
  ary[1]=5;

  print "in main num=", num;
  print "and ary[1]=", ary[1];

  # scalar passed by value and array passed by reference
  ans=ask(num, ary, "boy" );

  # num not changed in main, ary is
  #  and ans contains the 'changed' num value
  print "in main num=", num, " and ans=", ans;
  print "and ary[1]=", ary[1];
  
  # name is created inside function amd continues outside
  # lname was a 'local' declared in the declaration, 
  #   not passed out
  print name, lname;
}

# By passing lname and num, scalars, in, they become local in the function.
# Because ary is an array, it is passed by reference, which means not local.
# Howowever, name, not previously defined, becomes a global scalar value.
#
# A function can return a single argument (string)
# If a function is to 'return' multiple values, use an array created in
#   main and pass it in. The function can then modify elements of the array
#   which will then be available when function completes.
#
function ask (num, ary, lname)
{
   print "lname in", lname;
   name="tim"
   lname="tank" 
   var="in ask, num=";
   print var, num;
   num=4
   print "Num tweaked=", num
   print "local var with value passed in", lname

   ary[1]=3
   # only one argument can be returned
   # if two or more 'arguments' provided, they are 
   #   concatenated.
   return num 1
}

    Output : 
    in main num= 7
and ary[1]= 5
lname in boy
in ask, num= 7
Num tweaked= 4
local var with value passed in tank
in main num= 7  and ans= 41
and ary[1]= 3
tim

    Pre-defined

  • Numeric
  • String