Effective awk Programming, 3rd Edition

Chapter 10. Advanced Features of gawk

This chapter discusses advanced features in gawk. It’s a bit of a “grab bag” of items that are otherwise unrelated to each other. First, a command-line option allows gawk to recognize nondecimal numbers in input data, not just in awk programs. Next, two-way I/O, discussed briefly in earlier parts of this book, is described in full detail, along with the basics of TCP/IP networking and BSD portal files. Finally, gawk can profile an awk program, making it possible to tune it for performance.

The Section C.3 in Appendix C discusses the ability to dynamically add new built-in functions to gawk. As this feature is still immature and likely to change, its description is relegated to an appendix.

Allowing Nondecimal Input Data

If you run gawk with the --non-decimal-data option, you can have nondecimal constants in your input data:

$ echo 0123 123 0x123 |
> gawk --non-decimal-data '{ printf "%d, %d, %d\n", $1, $2, $3 }'
83, 123, 291

For this feature to work, write your program so that gawk treats your data as numeric:

$ echo 0123 123 0x123 | gawk '{ print $1, $2, $3 }'
0123 123 0x123

The print statement treats its expressions as strings. Although the fields can act as numbers when necessary, they are still strings, so print does not try to treat them numerically. You may need to add zero to a field to force it to be treated as a number. For example:

$ echo 0123 123 0x123 | gawk --non-decimal-data '
> { print $1, $2, $3
>  print $1 + 0, $2 ...