Question

I am pretty new to bash commands, and I’m trying to make a for statement that prints out each line with a value of 3 in the 6th column (space delimited) to a file. My syntax looks like this:

for i in `cat test`
do
section=`echo ${i} | cut -d ' ' -f 6`
line=`echo ${i}`
if [ ${section} == "3" ];
then
echo ${line} > test.out
fi
done

Unfortunately, this doesn’t work… Can anyone tell me what’s wrong with this?

Answer 1

You’re not reading the file the right way.

You can debug it by trying:

for i in `cat file.txt`
    echo $i
done

you will see that it prints each word on a new line, because the for-loop is actually iterating over each word in the file, instead of each line.

To read a file line by line use the following:

while IFS= read -r line
do
     echo "$line"
done < file.txt

By the way, if you want an alternative solution, you can use this awk one-liner:

awk '$6 == "3"' test > test.out