411 REFERENCE · Wikibooks
An Awk Primer/User-defined Functions
Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.
Awk supports user-defined functions.
Reusing code
A function definition is specified outside of patterns and actions and looks like:
function <name>(<comma-separated list of parameters>) { <actions> }
For example, the following program, for each record, prints sum of squares of its first two fields:
function print_sumsq(x, y) {
print x * x + y * y
}
NF >= 2 {
print_sumsq($1, $2)
}
A function call should not contain any intervening whitespaces between the function name and the left parenthesis. This applies only to user-defined functions, and the goal is to avoid confusion with the concatenation operator:
function print_sumsq(x, y) {
print x * x + y * y
}
NF >= 2 {
print_sumsq($1, $2); # Correct
print_sumsq ($1, $2); # Incorrect
print(atan2($1, $2)); # Correct
print(atan2 ($1, $2)); # Correct, as atan2 is not a user-defined function
}
In order to return a value, use the return statement:
function sumsq(x, y) {
return x * x + y * y
}
NF >= 2 {
print(sumsq($1, $2))
}
Local variables
In order to use local variables, they should be specified at the end of the parameter list, but not in the function call:
function sumsq(x, y, u, v) {
# u, v are local
u = x * x;
v = y * y;
return u + v
}
NF >= 2 {
print(sumsq($1, $2))
}
By convention, local variables are separated from parameters by extra spaces.
Indirect function calls
As a GAWK extension, there is an indirect function call. It looks like this:
@<a variable whose value is a function name>(comma-separated list of parameters>)
Example:
function print_sumsq(x, y) {
print x * x + y * y
}
BEGIN {
myfun = "print_sumsq"
}
NF >= 2 {
@myfun($1, $2)
}