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Get nth occurence of string from a file

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Top Forums Shell Programming and Scripting Get nth occurence of string from a file
# 8  
Old 04-10-2015
My txt file has data something like this,

Code:
01,0000000,xxxxxxx/                        
02,xxxxxxxx,yyyyyy/                                    
03,test1,41203016,,/      
01,0000000,xxxxxxx/                        
02,xxxxxxxx,yyyyyy/                                    
03,test2,41203017,,/     
01,0000000,xxxxxxx/     
04,xxxxx,00000,test2                   
02,xxxxxxxx,yyyyyy/                                    
03,test3,41203018,,/

I need to get the string 2nd column value after 03.
That means in this case it is test1, test2 and test3. The same string may exist in other lines too (like test2 exist in line starting 04 which I dont want to replace).

So this is what I am expecting..
get the value 'test1' and I am passing this to a prog. and getting replace string 'replace1' and then need to replace with this in the file.
similarly for test2 and test3.

I used this to get each occurence value, put it in variable and use sed to replace. But this is replacing 'test2' string in both line starting with 03 and 04.

Code:
$testvalue=`awk -F"," -v X="03" -v N=2 '($1 == X) && ((++L)>=(N+0)) { $2="replace2"; print $2 ; exit }'

$replacevalue='replace2'

sed "s/$testvalue/$replacevalue/" $1 > temp.txt

like this
Code:
01,0000000,xxxxxxx/                        
02,xxxxxxxx,yyyyyy/                                    
03,replace1,41203016,,/      
01,0000000,xxxxxxx/                        
02,xxxxxxxx,yyyyyy/                                    
03,replace2,41203017,,/     
01,0000000,xxxxxxx/     
04,xxxxx,00000,replace2                   
02,xxxxxxxx,yyyyyy/                                    
03,replace3,41203018,,/

So I am looking for single command which gets the string and also replaces it.
# 9  
Old 04-10-2015
Try

Code:
awk -F, '$1=="03"{gsub(/test/,"replace",$2)}1' OFS="," file

# 10  
Old 04-10-2015
Quote:
Originally Posted by senhia83
Try

Code:
awk -F, '$1=="03"{gsub(/test/,"replace",$2)}1' OFS="," file

Its working when I hard code the values but when I use the variables like this the its not replacing..

Code:
awk -F, '$1=="03"{gsub(/$l_test/,$l_replace,$2)}1' OFS="," file.txt > temp.txt

# 11  
Old 04-11-2015
Quote:
Originally Posted by r@v!7*7@
Its working when I hard code the values but when I use the variables like this the its not replacing..
Code:
awk -F, '$1=="03"{gsub(/$l_test/,$l_replace,$2)}1' OFS="," file.txt > temp.txt

You haven't defined any variables in this awk script except FS and OFS. In an ERE, $l_test is looking for end of field 2 followed by the string l_test in field 2 (which it will NEVER find) and for each time that it is found, will replace it with the entire input line (since undefined awk variables expand to 0 or an empty string depending on context, and in awk $ followed by a field number refers to the contents of that field). If you are saying that you have defined shell variables in your shell script:
Code:
l_test="test"
l_replace="replace"

and you want to use those variables as the extended regular expression search pattern and substitution replacement specification, respectively, inside your awk script, that could be done with something like:
Code:
l_test="test"
l_replace="replace"
awk -F, -v ERE="$l_test" -v rep="$l_replace" '$1=="03"{gsub(ERE,rep,$2)}1' OFS="," file.txt > temp.txt

Note that if your search pattern occurs multiple times in field 2 in your input, each occurrence will be replaced. If you just want to replace the first occurrence of the search pattern, you should change:
Code:
gsub(ERE,rep,$2)

to:
Code:
sub(ERE,rep,$2)

This User Gave Thanks to Don Cragun For This Post:
r@v!7*7@
# 12  
Old 04-11-2015
Quote:
Originally Posted by Don Cragun
You haven't defined any variables in this awk script except FS and OFS. In an ERE, $l_test is looking for end of field 2 followed by the string l_test in field 2 (which it will NEVER find) and for each time that it is found, will replace it with the entire input line (since undefined awk variables expand to 0 or an empty string depending on context, and in awk $ followed by a field number refers to the contents of that field). If you are saying that you have defined shell variables in your shell script:
Code:
l_test="test"
l_replace="replace"

and you want to use those variables as the extended regular expression search pattern and substitution replacement specification, respectively, inside your awk script, that could be done with something like:
Code:
l_test="test"
l_replace="replace"
awk -F, -v ERE="$l_test" -v rep="$l_replace" '$1=="03"{gsub(ERE,rep,$2)}1' OFS="," file.txt > temp.txt

Note that if your search pattern occurs multiple times in field 2 in your input, each occurrence will be replaced. If you just want to replace the first occurrence of the search pattern, you should change:
Code:
gsub(ERE,rep,$2)

to:
Code:
sub(ERE,rep,$2)

Thanks a lot. That was really helpful.
But even though I changed it to below, it is replacing mutiple occurrence's. Am I missing something.
Code:
sub(ERE,rep,$2)

[/QUOTE]
Last edited by r@v!7*7@; 04-11-2015 at 03:17 AM..
# 13  
Old 04-11-2015
Quote:
Originally Posted by r@v!7*7@
Thanks a lot. That was really helpful.
But even though I changed it to below, it is replacing mutiple occurrence's. Am I missing something.
Code:
sub(ERE,rep,$2)

Using gsub(ERE,rep,2 replaces every string matched by ERE in field 2 on each line with the replacement string indicated by rep.

Using sub(ERE,rep,2 replaces the 1st string matched by ERE in field 2 on each line with the replacement string indicated by rep.

With the sample input you provided and the sample output you said you wanted, both of these do exactly what you said you wanted. You did not provide any sample input with the string test appearing two or more times in field 2 on a line where the 1st field on that line is the string 03.
# 14  
Old 04-11-2015
Quote:
Originally Posted by Don Cragun
Using gsub(ERE,rep,2 replaces every string matched by ERE in field 2 on each line with the replacement string indicated by rep.

Using sub(ERE,rep,2 replaces the 1st string matched by ERE in field 2 on each line with the replacement string indicated by rep.

With the sample input you provided and the sample output you said you wanted, both of these do exactly what you said you wanted. You did not provide any sample input with the string test appearing two or more times in field 2 on a line where the 1st field on that line is the string 03.
you are right. But is there a way we can only replace only first occurrence of the string in a file for line starting with
Code:
03

.
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