HPR2438: Gnu Awk - Part 8

Hacker Public Radio

Gnu Awk - Part 8

Introduction

This is the eighth episode of the "Learning Awk" series that b-yeezi and I are doing.

Recap of the last episode

• The while loop: tests a condition and performs commands while the test returns true

• The do while loop: performs commands after the do, then tests afterwards, repeating the commands while the test is true.

• The for loop (type 1): initialises a variable, performs a test, and increments the variable all together, performing commands while the test is true.

• The for loop (type 2): sets a variable to successive indices of an array, preforming a collection of commands for each index.

These types of loops were demonstrated by examples in the last episode.

Note that the example for 'do while' was an infinite loop (perhaps as a test of the alertness of the audience!):

#!/usr/bin/awk -f BEGIN { i=2; do { print "The square of ", i, " is ", i*i; i = i + 1 } while (i != 2) exit; }

The condition in the while is always true:

The square of 2 is 4 The square of 3 is 9 The square of 4 is 16 The square of 5 is 25 The square of 6 is 36 The square of 7 is 49 The square of 8 is 64 The square of 9 is 81 The square of 10 is 100 ... The square of 1269630 is 1611960336900 The square of 1269631 is 1611962876161 The square of 1269632 is 1611965415424 The square of 1269633 is 1611967954689 The square of 1269634 is 1611970493956 ...

The variable i is set to 2, the print is executed, then i is set to 3. The test "i != 2" is true and will be ad infinitum.

Some more statements

We will come back to loops later in this episode, but first this seems like a good point to describe another statement: the switch statement.

Long notes

The notes for rest of this episode are available here.

Links

• GNU Awk User's Guide
• Previous shows in this series on HPR:
  • "Gnu Awk - Part 1" - episode 2114
  • "Gnu Awk - Part 2" - episode 2129
  • "Gnu Awk - Part 3" - episode 2143
  • "Gnu Awk - Part 4" - episode 2163
  • "Gnu Awk - Part 5" - episode 2184
  • "Gnu Awk - Part 6" - episode 2238
  • "Gnu Awk - Part 7" - episode 2330
• Resources:
  • ePub version of these notes
  • PDF version of these notes
  • Demonstration of the switch statement:
    • Script: switch_example.awk
    • Output: switch_example.out
  • Demonstration of the break statement:
    • Script: divisor.awk
    • Output: divisor.out
  • Demonstration of the continue statement:
    • Script: continue_example.awk
  • Demonstration of the next statement:
    • Script: next_example.awk
    • Output: next_example.out