How can I pass variable to "awk" and use print ?

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# 1  
Old 08-11-2011
Data How can I pass variable to "awk" and use print ?

Problem comes with following command:
[saturn@localhost Desktop]$ a=2
[saturn@localhost Desktop]$ awk  'NR==2 {print $2}' about.txt 
[saturn@localhost Desktop]$ awk  "NR==2 {print $2}" about.txt 
All rights reserved. Use is subject to license terms.           ????why print all fields????
[saturn@localhost Desktop]$ awk  "NR==$a {print $2}" about.txt 
All rights reserved. Use is subject to license terms.           ????why print all fields????
[saturn@localhost Desktop]$ awk  'NR==$a {print $2}' about.txt 
                                                               !!!print nothing!!!

Why does it print all fields? How to resolve it.
# 2  
Old 08-11-2011
awk  "NR==2 {print $2}" about.txt

The awk script is specified between ", so the shell makes the substition for $2 before awk execution.
# 3  
Old 08-11-2011
However I want to use $a, not "2", I want to use variable set by others in the awk.
# 4  
Old 08-11-2011
awk -v a=$a 'NR==$a {print $2}' about.txt
awk 'NR==$a {print $2}' a=$a about.txt

# 5  
Old 08-11-2011
Thanks, your command seems get nothing:
[saturn@localhost Desktop]$ echo $a
[saturn@localhost Desktop]$ awk 'NR==$a {print $2}' a=$a about.txt
[saturn@localhost Desktop]$ awk -v a=$a 'NR==$a {print $2}' about.txt
[saturn@localhost Desktop]$

What's wrong?
# 6  
Old 08-11-2011
Oups !
awk -v a=$a 'NR==a {print $2}' about.txt
awk 'NR==a {print $2}' a=$a about.txt

# 7  
Old 08-11-2011
Thanks all !!
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