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Old 11-11-2011, 11:04 AM   #1
cristalp
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AWK: match multiple strings in the file, print 1 when match and 0 when not


Dear Experts,

I just want to achieve a very simple function by awk that when there matchs a string "A" or "B" in the file, print 1 otherwise print 0.

How could I do this simply without if else?
 
Old 11-11-2011, 11:34 AM   #2
colucix
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Do you want to match both the string or at least one of them? And must the strings be in the same line or can they be on different lines?

This one matches both the strings on different lines:
Code:
awk '/A/{one=1}/B/{two=1}END{print (one+two==2)}' file

Last edited by colucix; 11-11-2011 at 11:35 AM.
 
Old 11-11-2011, 11:54 AM   #3
grail
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Alternative:
Code:
awk '/A|B/{print "1";exit}END{print "0"}' file
 
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Old 11-11-2011, 05:13 PM   #4
cristalp
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Quote:
Originally Posted by colucix View Post
Do you want to match both the string or at least one of them? And must the strings be in the same line or can they be on different lines?

This one matches both the strings on different lines:
Code:
awk '/A/{one=1}/B/{two=1}END{print (one+two==2)}' file
Thanks! But I just want to match one of them. "A" OR "B". I mean, as long as there is string match "A" or "B", I got a print out 1. If there is there is neither "A" nor "B" in the file, print 0.
 
Old 11-11-2011, 10:16 PM   #5
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a tad better (but slower), easy to mod.
Code:
awk 'BEGIN { count=0;} $0 ~ /(A)|(B)/ { count++; } END { print "Number of times the patterns were seen =",count;}' infile
 
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Old 11-12-2011, 02:01 AM   #6
colucix
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Quote:
Originally Posted by cristalp View Post
Thanks! But I just want to match one of them. "A" OR "B". I mean, as long as there is string match "A" or "B", I got a print out 1. If there is there is neither "A" nor "B" in the file, print 0.
A slight modification to the suggested code: put >=1 in place of ==2. Easy.
 
Old 11-15-2011, 08:10 AM   #7
cristalp
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Quote:
Originally Posted by grail View Post
Alternative:
Code:
awk '/A|B/{print "1";exit}END{print "0"}' file
Thank you for your code. I tired it. When there is no A and no B in my file, the output is "0" which is what I want. But when there is a A or B in my file, the output is
Code:
1
0
which has a redundant "0" at newline. That is not what I want.

I think your code is the easiest to understand. I don't know where it is wrong, may be the "exit"? Do you have any ideas.
Thanks anyway!
 
Old 11-15-2011, 08:23 AM   #8
cristalp
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Originally Posted by colucix View Post
A slight modification to the suggested code: put >=1 in place of ==2. Easy.
Thank you! It works. Could you explain a bit what the meaning of print (one+two>=1)?

what I understood is, this code search A and B separately. If it find a string match "A" it send 1 to variable "one", if it find a string match "B" it send 1 to variable "two". So, if there is no match what value would be send to "one" and "two"? Is that 0??

And then print the result for one+two if one+two larger or equal then 1. So, if there are both "A" and "B" found in the file, one+two should equal to 2, why the output is still 1 in this case?

Or, if there is no "A" and no "B" in the file, own+two now is smaller than 1, why AWK is still able to print 0?

My understanding for the meaning of print (one+two>=1) must be wrong, so what is its correct meaning?
Thanks!!!
 
Old 11-15-2011, 08:31 AM   #9
colucix
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Quote:
Originally Posted by cristalp View Post
Could you explain a bit what the meaning of print (one+two>=1)?

what I understood is, this code search A and B separately. If it find a string match "A" it send 1 to variable "one", if it find a string match "B" it send 1 to variable "two". So, if there is no match what value would be send to "one" and "two"? Is that 0??
Yes. In AWK an uninitialized variable has value 0 if treated arithmetically, is a null string otherwise. The operation one+two causes the variables to be numeric.
Quote:
Originally Posted by cristalp View Post
And then print the result for one+two if one+two larger or equal then 1. So, if there are both "A" and "B" found in the file, one+two should equal to 2, why the output is still 1 in this case? Or, if there is no "A" and no "B" in the file, own+two now is smaller than 1, why AWK is still able to print 0?
The expression is a logical statement which in awk translates to 0 (false) or 1 (true). This is common to many other scripting languages: if you print out a logical variable or expression you will see 0 or 1.
 
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Old 11-15-2011, 08:36 AM   #10
colucix
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Quote:
Originally Posted by cristalp View Post
I don't know where it is wrong, may be the "exit"? Do you have any ideas. Thanks anyway!
On behalf of grail, I can tell that indeed the exit statement is the problem. The logic is correct (as soon as it encounters A or B the program should print out 1 and exit, without further processing). However in awk the exit statement doesn't prevent the execution of the END block (if present). A slightly different approach, similar to mine could be:
Code:
awk '/A|B/{var=1}END{print var+0}' file
The notation var+0 is necessary to print out the value of 0. Try to remove the +0 part and see the difference.
 
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Old 11-15-2011, 09:57 AM   #11
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Sorry about that ... it was 3am and wasn't paying attention Thank you to colucix for the altered solution
 
Old 11-15-2011, 10:06 AM   #12
colucix
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Quote:
Originally Posted by grail View Post
Sorry about that ... it was 3am and wasn't paying attention
We forgive you!
 
Old 11-15-2011, 10:18 AM   #13
cristalp
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Thanks for colucix's excellent explanations and the help from grail and Linux_Kidd, all together I get a deeper understanding for AWK at the end. Thanks a lot for your patient and kind teaching.
 
  


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