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  #1 (permalink)  
Old 01-28-2009
javathecat javathecat is offline
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Posts: 5
sed in while loop producing arithmetic output
Hi all

Just wondering if someone can help me with this. I'm trying to write a script that processes the output of another file and prints only the lines I want from it.

This is only the second script I have written so please bare with me here. I have referred to the literature and some of the previous posts and I'm sure I have the logic and syntax correct. It computes, but it takes ages and gives me the wrong output.

heres the code:

#Set the line number variables
filelinenumber=1
datalinenumber=8

lines=`sed -n '$=' test1.out`

while [ $datalinenumber -le $lines ]
do

# print the selected lines into the new file mpck2.out
sed -n "${filelinenumber}p" test1.out` > mpck2.out
sed -n "${datalinenumber}p" test1.out > mpck2.out

# increment the line number variables
filelinenumber=`expr $filelinenumber + 11`
datalinenumber=`expr $datalinenumber + 11`

done

Instead of a file full of the program lines I want I'm just getting this
$ cat mpck2.out
average 156956
  #2 (permalink)  
Old 01-28-2009
cfajohnson's Avatar
cfajohnson cfajohnson is offline Forum Advisor  
Shell programmer, author
  
 

Join Date: Mar 2007
Location: Toronto, Canada
Posts: 2,362
Quote:
Originally Posted by javathecat View Post
This is only the second script I have written so please bare with me here.

Sorry, I don't know you well enough to bare with you ... or do you mean bear with me?
Quote:
I have referred to the literature and some of the previous posts and I'm sure I have the logic and syntax correct. It computes, but it takes ages and gives me the wrong output.

It takes ages because you are calling sed many, many times.
Quote:

heres the code:

Please put code inside [code] tags.
Quote:

Code:
#Set the line number variables
filelinenumber=1
datalinenumber=8

lines=`sed -n '$=' test1.out`

The usual way to count the number of lines in a file is:

Code:
line=$( wc -l < "$FILE" )

Quote:
Code:
while [ $datalinenumber -le $lines ]
do

# print the selected lines into the new file mpck2.out
sed -n "${filelinenumber}p" test1.out` > mpck2.out
sed -n "${datalinenumber}p" test1.out > mpck2.out
# increment the line number variables
filelinenumber=`expr $filelinenumber + 11`
datalinenumber=`expr $datalinenumber + 11`

done

Every time you use > mpck2.out, you are truncating the file before writing to it.

Instead, redirect the output of the loop:


Code:
while [ $datalinenumber -le $lines ]
do
  # print the selected lines into the new file mpck2.out
  sed -n "${filelinenumber}p" test1.out`
  sed -n "${datalinenumber}p" test1.out

  # increment the line number variables (no need for expr)
  filelinenumber=$(( $filelinenumber + 11 ))
  datalinenumber=$(( $datalinenumber + 11 ))
done > mpck2.out

Quote:
Instead of a file full of the program lines I want I'm just getting this
$ cat mpck2.out
average 156956

It would be better done in awk


Code:
awk ' BEGIN { fln = 1; dln = 8 }
NR == fln || NR == dln { print }
      { fln += 11; dln += 11 }
' test1.out > mpck2.out
  #3 (permalink)  
Old 01-29-2009
javathecat javathecat is offline
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Join Date: Jan 2009
Posts: 5
Excellent! It Works. I Appreciate your help with that.

Its very good to see the code work.

I will take a look at implementing the awk solution also if it requires less computation. I did notice that others have been referred to it in quite a few of the other posts.

Cheers
  #4 (permalink)  
Old 02-04-2009
javathecat javathecat is offline
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Join Date: Jan 2009
Posts: 5
I got the awk code to work too. It's impressively faster than calling sed.

This code didn't quite work on my machine:

Code:
awk ' BEGIN { fln = 1; dln = 8 }
NR == fln || NR == dln { print }
      { fln += 11; dln += 11 }
' test1.out > mpck2.out

However this did and it definitely pointed me in the right direction:

Code:
awk ' BEGIN { fln = 1; dln = 8 }
      NR == fln {print; fln += 11}
      NR == dln {print; dln += 11}
' test1.out > mpckawk2.out
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