CODEWITHSUNDEEP
awk
Jerry Smith
Jerry Smith

Reputation: 91

What does it mean when an awk script has code outside curly braces?

Going through an awk tutorial, I came across this line

substr($0,20,5) == "HELLO" {print}

which prints a line if there is a "HELLO" string starting at 20th char.

Now I thought curly braces were necessary at the start of an awk script and an 'if' for this to work, but it works without nevertheless.

Can some explain how it evaluates?

Upvotes: 2

Views: 781

Answers (1)

Charles Duffy
Charles Duffy

Reputation: 295687

If you have:

{ action }

...then that action runs on every line. By contrast, if you have:

condition { action }

...then that action runs only against lines for which the condition is true.

Finally, if you have only a condition, then the default action is print:

NR % 2 == 0

...will thus print every other line.

You can similarly have multiple pairs in a single script:

condition1 { action1 }
condition2 { action2 }
{ unconditional_action }

...and can also have BEGIN and END blocks, which run at the start and end of execution.

Upvotes: 6

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