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Print individual rows.

 
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# 1  
Old 07-05-2011
Print individual rows.
Hi all,
I have a file im reading with a for loop using:
Code:
for i in $(cat filename)
do
  etc.
done

the original file is 3 columns, this method prints it out into 3 rows, and i would like to just assign the first to rows (originally first two columns) to separate variables. What would be the easiest way to do this?

I tried to awk and fprint, and sed to print just the second row (line), but this did not work, because the individual lines are not files.
Last edited by Scott; 07-07-2011 at 12:22 PM.. Reason: Code tags
# 2  
Old 07-05-2011
Quote:
Originally Posted by jgrosecl
Hi all,
I have a file im reading with a for loop using:

for i in $(cat filename)
That's a useless use of backticks and useless use of cat. This is dangerous because if the file is large you can easily exceed the size limit of a shell variable. It's also inefficient. Better and safer is:

Code:
while read i
do
    ...
done <filename

'read' is even a shell internal.

Quote:
the original file is 3 columns, this method prints it out into 3 rows, and i would like to just assign the first to rows (originally first two columns) to separate variables. What would be the easiest way to do this?
The while read syntax does this for you too, reading line-by-line into whatever variables you tell it to:

Code:
# 'rest' is necessary because with just a b, given '1 2 3', it will set a=1, b="2 3"
while read a b rest
do
       ...
done < filename

What it splits variables on is controllable by the IFS variable, so if you had a file seperated by , instead of whitespace you could do
Code:
while IFS="," read a b rest
do
       ...
done < filename

This User Gave Thanks to Corona688 For This Post:
jgrosecl
# 3  
Old 07-06-2011
Thank you, the while loop is working quite well for me, perhaps you could also help me with the problem I am having now, if its not too much trouble:
Code:
while read a b c
do
  for line in $c
  do
    for i in $b
    do
      wanted_line3=$(grep "$i" /XXXX/XXXX/XXXX/XXXX/*)
      new_name3=$(echo "$wanted_line3" | sed "s/$i/$line/")
      echo $wanted_line3
      echo $new_name3
    done
  done
done< /XXXX/XXXX/XXXX/X.txt

This is turning out quite messy. I am trying to take the argument in each line of b and c, search for lines containing each line of b in a directory, and then replace it with c from the same column row.

Maybe I'm making this a lot harder than it actually needs to be.
Last edited by Scott; 07-07-2011 at 12:21 PM.. Reason: Code tags, please...
# 4  
Old 07-07-2011
Maybe. Could you show the input data you have and the output data you want?
 
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