Where are the simple AWK examples to get started?

Question

All of my codes fail. They should print "he", "hello" and "5 \n 3", respectively:

awk -v e='he' {print $e}       // not working, why?
awk NF { print hello }
awk { print ARGV[5,3] }

Are there some simple examples about AWK?

Answer 1

For the first, you don't use $ for variables inside awk, try this instead:

fury> echo | awk -v e='he' '{print e}'
he

For the second, your condition NF means NF!=0 so it will only print for non empty lines:

fury> echo | awk 'NF {print "hello"}'
fury> echo "7 8" | awk 'NF {print "hello"}'
hello

I've never seen your syntax for the third one, ARGV is a single dimensional array, so you can use:

fury> awk 'BEGIN {print ARGV[5]}' 1 2 3 4 5 6 7
5
fury> awk 'BEGIN {print ARGV[5] "\n" ARGV[3]}' 1 2 3 4 5 6 7
5
3

Note I'm using a BEGIN block for the third, otherwise it'll try to open and process 1, 2, 3, ... as files.

Answer 2

I use this site. The O'Reilly Sed & Awk book is good as well.

Answer 3

Try:

echo "hello" | awk ' {print $0} '
echo "hello" | awk ' {print $1} '

Note that $0 returns the whole record, and $1 just the first entry; awk starts its counters at 1. So

echo "hello1 hello2 hello3" | awk ' {print $0} '

returns hello1 hello2 hello3. While

echo "hello1 hello2 hello3" | awk ' {print $3} '

will return hello3

I like this awk tutorial.

Answer 4

First, basic shell scripting sanity:

• Always enclose your script in single quotes

Note that the script is a single argument - or a filename with '-f file'.

An awk script is a sequence of '<pattern> <action>' pairs. The action is enclosed in braces '{}' for clarity - and sanity, again.

As Pax said, the first example should be:

awk -v -e e='he' '{ print e }'

The second example is inscrutable - you probably meant:

awk '{ print "hello" }'

The variable NF is the number of fields on the line. You might get awk to interpret

awk 'NF { print "hello" }'

as if there is any data on the input line (NF != 0, or number of fields is not zero), then print 'hello'.

The last example is likewise inscrutable; ARGV is an array of the arguments to 'awk', and the command line provided none. But it is a one-dimensional array. Your sub-scripting notation wants to treat it like a Python dictionary or Perl hash, with two indexes combined. You're OK - awk supports associative arrays; but since you didn't add anything to the array at ARGV[5,2], it won't print anything.

Answer 5

nice tutorial on http://www.w3reference.com

Answer 6

Also, lots of useful info and tutorials at http://awk.info