This chapter describes awk’s built-in functions,
which fall into three categories: numeric, string, and I/O.
gawk provides additional groups of functions
to work with values that represent time, do
bit manipulation, sort arrays,
provide type information, and internationalize and localize programs.
Besides the built-in functions, awk has provisions for
writing new functions that the rest of a program can use.
The second half of this chapter describes these
user-defined functions.
Finally, we explore indirect function calls, a gawk-specific
extension that lets you determine at runtime what function is to
be called.