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grep a string in a file

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# 1  
Old 04-13-2012
grep a string in a file
Hi ,

i'm trying to create a code for the belwo scenario.

i have a data in a file file.txt like below.

Code:
ram
dept
comp
shyam
field
comp

Now i need write a code to find the string which is always 2 lines before the string "comp"

Can you please help me in this.

Thanks in advance
Last edited by Scrutinizer; 04-13-2012 at 05:38 PM.. Reason: code tags
# 2  
Old 04-13-2012
grep is not a programming language. it can't be told to rewind 2 lines and print if it finds a match.

awk is a programming language and, while it can't rewind, it can save lines for later:

Code:
awk '{ LINES[(++L)%3]=$0 }; /comp/ && (L>2) { print LINES[(L-2)%3] }' filename

This User Gave Thanks to Corona688 For This Post:
p.bhaskar
# 3  
Old 04-13-2012
Use this code. Just one line would do the job for you
Code:
nawk 'c-->0;$0~s{if(b)for(c=b+1;c>1;c--)print r[(NR-c+1)%b];print;c=a}b{r[NR%b]=$0}' b=2 a=0 s="comp" file.txt

You can change the "b" and "a" variables to match your criteria.
use "b" to get lines above and "a" to get lines below your string pattern ("s" variable is pattern)
eg: b=0 and a=2 will give you two lines below the string (shyam and field in this case)
This User Gave Thanks to grep_me For This Post:
p.bhaskar
# 4  
Old 04-13-2012
Hi ,

Thanks for the quick reply.It's giving me the correct o/p.Say if i need to finf a string 26 lines before "comp" string do i need to write then?

---------- Post updated at 11:04 AM ---------- Previous update was at 11:01 AM ----------

Hi ,

Thanks for the reply.
I have run the code sent by you which is giving me all the strings for b=2 and a=0
# 5  
Old 04-13-2012
Code:
grep -B2 comp <file>

Well this is not the ideal solution! as different systems have different flavors of grep

See if it matches with your requirement. Personally i would not use grep to do this because it will add "external" dependency for your script.
# 6  
Old 04-13-2012
I thought you needed 2 lines above the string you wanted. isnt it?
the code above gives you 2 lines above and 0 lines below the string including the string you wanted.
# 7  
Old 04-13-2012
Thanks for the reply.
Here in the file i put 2 lines above only.
Actually my requirement is to print the string which is 26 lines above every occurence of "comp" string only.

Sorry if i have misguided you.
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