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Old 10-20-2011, 03:59 PM   #1
Tech109
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grep behavior using a 'for' loop


Hi, I'm puzzled as to why grep behaves differently under these two circumstances:

>grep -e String_To_Find filename.txt

-Returns just the line with exact match for String_To_Find


>for i in stringsfile.txt; do grep -e filename.txt; done

-Returns results as if it's not obeying the '-e' flag.


What I'm trying to accomplish is use a text file containing a list of strings, come which contain spaces in between and some which do not, and feed them into a loop to search for each exact match of the string in another file. I have even tried listing the strings out of the strings file using echo $(cat stringsfile.txt) and then iterating through that list, but same result.

I've tried bounding the variable with ^ and $, tried variations of single quotes, double-quotes, no quotes, but nothing seems to work.
 
Old 10-20-2011, 04:09 PM   #2
Tech109
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Ok, so I had better results using this:

>grep -f stringsfile.txt filename.txt

But I still get some inaccurate matches.

The strings in stringsfile.txt are each on a separate line, with no single or double-quotes. The file contains 43 lines of strings, but the result I get returns 58 lines, because it is matching greedily, not exactly.
 
Old 10-20-2011, 04:12 PM   #3
SecretCode
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Is your quoted code complete? You are not using the $i variable. (Use [ CODE ] tags e.g via the # button around code snippets.)

As I understand it the -e parameter does not change the behaviour of grep - it's just a way to highlight the pattern when it would be ambiguous. But -E does change behaviour. Did you mean -E?
 
Old 10-20-2011, 04:14 PM   #4
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Cross-posted with your reply ... I think it would be useful if you can post a minimal (2 or 3 lines) example of patterns and a file that illustrates the problem.
 
Old 10-20-2011, 05:30 PM   #5
Tech109
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Sorry, I ommitted the $i variable...

Code:
for i in stringsfile.txt; do grep -e $i filename.txt; done
Or,

Code:
for i in ABCD HIJK LMNO PQRS TUVW; do grep -e $i filename.txt; done
So here's a hypothetical example of a string that I'm searching for an exact match on:

ABCD

I know this string exists in the master file that I'm grepping, but I need to see additional information about it (it's a database item that I need to configure).


So in the master file I'm grepping, there are many lines with strings that contain ABCD:

1234 ABCD char 100 # Description of what it is used for
1235 ABCD_History char 100 # Description of what it is used for
1236 Admin_ABCD char 100 # Description of what it is used for
1237 "ABCD Billing" char 100 # Description of what it is used for


Now the only one I'm interested in returning is the ABCD line, but my search using a loop will return all the lines listed above. I need to see this line because it tells me this is a character type (vs float) and it can hold 100 characters.

Hope this helps, and thanks for responding.

Last edited by Tech109; 10-20-2011 at 05:36 PM. Reason: Added CODE tags
 
Old 10-20-2011, 06:59 PM   #6
syg00
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regex is always (?) greedy. You might be able to get away with using word bounding (probably not given that snippet), or better specify your regex to do what you want.
 
Old 10-21-2011, 03:49 AM   #7
crts
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Quote:
Originally Posted by syg00 View Post
regex is always (?) greedy.
AFAIK, that is true for grep and most other standard tools in Linux.
Exceptions I know of are perl RegEx and Java RegEx which allow you to additionally specify non-greedy RegEx.

http://www.troubleshooters.com/codec...reg.htm#Greedy
http://download.oracle.com/javase/tu...gex/quant.html
 
Old 10-21-2011, 05:30 AM   #8
berbae
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Code:
for i in ABCD HIJK LMNO PQRS TUVW; do
    grep -w "$i" filename.txt
done
The -w option (--word-regexp) matches only whole words.

If you don't want the search string inside double quotes as you post #5 seems to tell:
Code:
for i in ABCD HIJK LMNO PQRS TUVW; do
    grep -w "$i" filename.txt|grep -v "\".*${i}.*\""
done

Last edited by berbae; 10-21-2011 at 11:24 AM.
 
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Old 11-08-2011, 05:23 PM   #9
Tech109
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Thanks everyone for responding, and to berbae, for providing the solution, although I stumbled upon it myself before coming back here.

What worked was the following:

Code:
for i in ABCD HIJK LMNO PQRS TUVW; do
    grep -w "$i" filename.txt
done
The key being the double-quotes around the variable.
 
  


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