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Problem with syntax using awk

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# 1  
Old 08-18-2010
Problem with syntax using awk
Hi Guys,
When below code is executed in script, I get desired output in output file.

Code:
awk 'NR >= $start_line  && NR <= 3' master_scriptlist.txt > $driver1/scriptlist.txt

But when i replace 3 with a variable end_line=3, I do not get ouput. See code below. Is there any problem with syntax

Code:
awk 'NR >= $start_line  && NR <= $end_line' master_scriptlist.txt > $driver1/scriptlist.txt

# 2  
Old 08-18-2010
You need to quote your variable this way:
Code:
awk 'NR >= '"$start_line"'  && NR <= '"$end_line"'' master_scriptlist.txt > $driver1/scriptlist.txt



---------- Post updated at 08:51 AM ---------- Previous update was at 08:45 AM ----------
Quote:
Originally Posted by ajincoep
Hi Guys,
When below code is executed in script, I get desired output in output file.

Code:
awk 'NR >= $start_line  && NR <= 3' master_scriptlist.txt > $driver1/scriptlist.txt

But I am curious how the code above works...
# 3  
Old 08-18-2010
I prefer

Code:
awk -vstart=$start_line -vend=$end_line 'NR >= start  && NR <= end ' master_scriptlist.txt > $driver1/scriptlist.txt

# 4  
Old 08-18-2010
Quote:
Originally Posted by kevintse
But I am curious how the code above works...
The action to take when the condition is true is omitted and by default implies that $0 is printed. Longer form, which might be more understandable, would be:
Code:
awk '
   NR >= $start_line  &&  NR <= 3 { 
        print;
   }' master_scriptlist.txt > $driver1/scriptlist.txt

@rdcwayx -- I'm with you on that 100%. Stitching together quoted segments to incorporate shell variables will end badly at some point in time.
# 5  
Old 08-18-2010
Quote:
Originally Posted by agama
The action to take when the condition is true is omitted and by default implies that $0 is printed. Longer form, which might be more understandable, would be:
Code:
awk '
   NR >= $start_line  &&  NR <= 3 { 
        print;
   }' master_scriptlist.txt > $driver1/scriptlist.txt

I know that, I am just wondering how the code works while the "$start_line" variable is inserted directly into the awk code, I think this is undefined, and the code does not work here.

Quote:
Originally Posted by agama
@rdcwayx -- I'm with you on that 100%. Stitching together quoted segments to incorporate shell variables will end badly at some point in time.
Yea, it is much better to use -v option, I learned something, thank you.
# 6  
Old 08-18-2010
Quote:
Originally Posted by kevintse
I know that, I am just wondering how the code works while the "$start_line" variable is inserted directly into the awk code, I think this is undefined, and the code does not work here.
Sorry, didn't mean to insult you Smilie

I see what you are saying (in addition to the typo that I cut/pasted into my example). It's possible that awk is interpreting $start_line as 0, which would always be true, but I cannot reproduce it, so I'm not sure.
# 7  
Old 08-19-2010
Thank you for responding.

Could you please answer these questions
1. When do we enclose quotes (" ") within a variable?
2. When do we enclose quotes (` `) within a variable?
3. When do we enclose both the above quotes within a variable?

For eg
Code:
awk 'NR >= '"$start_line"'  && NR <= '"$end_line"'' master_scriptlist.txt > $driver1/scriptlist.txt

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