Function Definition Examples

Here is an example of a user-defined function, called myprint, that takes a number and prints it in a specific format.

function myprint(num)
{
     printf "%6.3g\n", num
}

To illustrate, here is an awk rule which uses our myprint function:

$3 > 0     { myprint($3) }

This program prints, in our special format, all the third fields that contain a positive number in our input. Therefore, when given:

 1.2   3.4    5.6   7.8
 9.10 11.12 -13.14 15.16
17.18 19.20  21.22 23.24

this program, using our function to format the results, prints:

   5.6
  21.2

This function deletes all the elements in an array.

function delarray(a,    i)
{
    for (i in a)
       delete a[i]
}

When working with arrays, it is often necessary to delete all the elements in an array and start over with a new list of elements (see section The delete Statement). Instead of having to repeat this loop everywhere in your program that you need to clear out an array, your program can just call delarray.

Here is an example of a recursive function. It takes a string as an input parameter, and returns the string in backwards order.

function rev(str, start)
{
    if (start == 0)
        return ""

    return (substr(str, start, 1) rev(str, start - 1))
}

If this function is in a file named `rev.awk', we can test it this way:

$ echo "Don't Panic!" |
> gawk --source '{ print rev($0, length($0)) }' -f rev.awk
-| !cinaP t'noD

Here is an example that uses the built-in function strftime. (See section Functions for Dealing with Time Stamps, for more information on strftime.) The C ctime function takes a timestamp and returns it in a string, formatted in a well known fashion. Here is an awk version:

# ctime.awk
#
# awk version of C ctime(3) function

function ctime(ts,    format)
{
    format = "%a %b %d %H:%M:%S %Z %Y"
    if (ts == 0)
        ts = systime()       # use current time as default
    return strftime(format, ts)
}

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