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Old 09-02-2010, 03:57 AM   #1
babaqga
LQ Newbie
 
Registered: Aug 2010
Posts: 18

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awk for-loop


Hi guys,

I am writing a simple bash script looking like this:
LOOP1
Code:
#!/bin/bash
...
echo $OUTPUT | awk '{
for (i="'"$NRCORES"'";i<="'"$ENDLOOP"'";i++)
print $i
}'
My problem is that the script doesn't output anything
BUT !
If I change it to the following:
LOOP2
Code:
#!/bin/bash
echo $OUTPUT | awk '{
for (i=8;i<=17;i++)
print $i
}'
It gives me what it is supposed to give (the 8-th to 17-th column of the $OUTPUT variable)

Strangely, if I echo $NRCORES or $ENDLOOP in the script I get 8 and 17 respectively, so in my view LOOP1 is exactly the same as LOOP2. However, awk doesn't seem to agree with me. In addition, I know for sure that when awk encounters a non-numeric variable in the print statement, it will take it as a zero and print the whole string. Therefore, I don't see what the problem can be.
WHAT IS WRONG WITH IT ?
please respond

Last edited by babaqga; 09-02-2010 at 04:03 AM.
 
Old 09-02-2010, 04:02 AM   #2
druuna
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Registered: Sep 2003
Posts: 10,532
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Hi,

This works:
Code:
#!/bin/bash

OUTPUT="1234567890"
NRCORES=4
ENDLOOP=6

echo $OUTPUT | awk '{
for (i='$NRCORES';i<='$ENDLOOP';i++)
print i
}'
Mind the quoting and the print i (not $i)

Hope this helps.
 
Old 09-02-2010, 04:08 AM   #3
babaqga
LQ Newbie
 
Registered: Aug 2010
Posts: 18

Original Poster
Rep: Reputation: 1
Quote:
Originally Posted by druuna View Post
Hi,

This works:
Code:
#!/bin/bash

OUTPUT="1234567890"
NRCORES=4
ENDLOOP=6

echo $OUTPUT | awk '{
for (i='$NRCORES';i<='$ENDLOOP';i++)
print i
}'
Mind the quoting and the print i (not $i)

Hope this helps.
Yep, it helped, with the exception I want not the i itself, but the $i. Anyway, you were right for the quoting.

Last edited by babaqga; 09-02-2010 at 04:09 AM.
 
Old 09-02-2010, 04:17 AM   #4
druuna
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Registered: Sep 2003
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Hi,

Which $i are you talking about?

The for loop with the i=x;i<=y;i++ part is were i is generated (not $i). This is how awk works.

Maybe you should tell us what it is you are trying to accomplish so we can come up with code that suits that.

Hope this helps.
 
Old 09-02-2010, 04:57 AM   #5
ghostdog74
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Registered: Aug 2006
Posts: 2,697
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use the -v option of awk to pass in shell variables to awk. Its "preferred" , than messy quoting.
Code:
#!/bin/bash
...
NRCORES="something"
ENDLOOP="something"

echo $OUTPUT | awk -vnc="$NCORES" -v el="$ENDLOOP" '{
for (i=nc;i<=el;i++)
  print $i
}'
 
  


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