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bashawkvariable-assignment
user3375672
user3375672

Reputation: 3768

basic understanding of variable assignment in awk

I am having a very basic quarrel with my understanding of awk's way of using variable assignment. In the below how come the output from the variable new that I assign is not printed - instead the whole record ($0) get printed. I did look trough the GNU user's guide but failed to comprehend this very fundamental behavior. Thanks for the patience!

echo "a b c" | awk '
{
print $NF #This prints c    
new=$NF
print $new #Why does this not print c 
}'

Output:

c
a b c

Upvotes: 1

Views: 357

Answers (3)

gbarry
gbarry

Reputation: 10552

It is tempting to associate the $ with strings, as some languages use this convention. Furthermore, shells such as bash use the $ to retrieve a variable value. And the most confusing thing is, both the shell and awk use $ with a number to parse fields from a complete line. So $1 contains the first field, and so on. But nowhere else do variables in awk use the dollar sign.

Upvotes: 0

Linga Murthy C S
Linga Murthy C S

Reputation: 5432

You can update the line to print to print new; Accessing variables is C-type in awk.

new=$NF is same as:
new=$3 (the value of NF is evaluated to 3)

And now that the variable new has the value of 3rd column(c), you can use: print new

Else, as per @anubhava's answer, you can assign the value of NF to new and use it with the $ symbol to print the 3rd column.

Upvotes: 0

anubhava
anubhava

Reputation: 784878

To understand difference use this code:

echo "a b c" | awk '
{
print $NF #This prints c    
new=NF
print $new #Why does this not print c 
}'

Output: It correctly prints:

c
c

When you use new=$NF instead of new=NF you assign value of last field into new. And then when you do $new again in print statement then awk attempts to convert c to a number and gets 0 hence it prints whole line.

Upvotes: 3

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