how to cat command output to string in shell script

Question

in my script i need to loop through lines in a file, once i find some specific line i need to save it to variable so later on i can use it outside the loop, i tried the following but it wont' work:

count=0
res=""
python my.py -p 12345 |
  while IFS= read -r line
  do
     count=$((count+1))
     if [ "$count" -eq 5 ]; then
        res=`echo "$line" | xargs`
     fi
  done
echo "$res"

it output nothing, i also tried this,

res=""

... in the loop...
   res=$res`echo "$line" | xargs`

still nothing. please help. thanks.

Update: Thanks for all the help. here is my final code: res=python my.py -p 12345 | sed -n '5p' | xargs

@anubhava: the input is an command output. updated in the post — user468587
– user468587, Commented Feb 27, 2015 at 22:38

Matt · Accepted Answer · 2015-02-27 22:43:25Z

1

for finding a specific line in a file, have you considered using grep?

grep "thing I'm looking for" /path/to/my.file

this will output the lines that match the thing you're looking for. Moreover this can be piped to xargs as in your question.

If you need to look at a particularly numbered line of a file, consider using the head and tail commands (which can also be piped to grep).

cat /path/to/my.file | head -n5 | tail -n1 | grep "thing I'm looking for"

These commands take the first lines specified (in this case, 5 and 1 respectively) and only prints those out. Hopefully this will help you accomplish your task.

Happy coding! Leave a comment if you have any questions.

edited Feb 27, 2015 at 22:43

answered Feb 27, 2015 at 22:19

Matt

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