Understand a search pattern in AWK?

Question

I am reading section 2.3 of the tutorial at - http://www.vectorsite.net/tsawk_2.html#m2

There is more to Awk's string-searching capabilities. The search can be constrained to a single field within the input line.

For example:

$1 ~ /^France$/

There is no code to which shows how this pattern works. Can someone show me how this line can be used and how it works ?

Answer 1

Sure!

$1 ~ /^France$/

With the following awk command:

awk '$1 ~ /^France$/ { print }'

And the following input

France 1
France1 2
france 3
- France 4
France - 5

The output will be

France 1
France - 5

$1 is the value of the first field; the default for awk is to split using whitespace delimited fields. The /^France$/ is the regular expression matching the exact string France (using start-of-string and end-of-string anchors ^ and $ ). And finally, ~ , is a binary string operator that matches the left-hand side by the regular expression on the right-hand side.

Note that regular expressions can be expressed as normal quoted strings or given in variables as well, but the "/.../" syntax is better when the expression is inline as it's more obvious and there's no need for extra escaping that strings cause when there's either a quote or a backslash in the expression.

Of course, that particular expression would be simpler as $1 == "France" .

Let me know if a more complex example will help.

Answer 2

To learn awk, get the book Effective Awk Programming, Third Edition By Arnold Robbins. Don't rely on random web sites to have accurate or useful information.