bash shell script read file line by line. - Page 2

d.anitkumar · 10-03-2007, 06:15 AM

Hi This is my script like..
while read line
do
myval="DAKS"
done
echo $myval

i am not getting the value output outside the while loop
help me out if u havr some others

ghostdog74 · 10-03-2007, 07:34 AM

Quote:

Originally Posted by Darren[UoW]

I am using the following code to read line by line from a file, however my problem is that $value=0 at the end of the loop possibly because bash has created a subshell for the loop or something similar. How can I solve this.

value=0;

while read line
do
value=`expr $value + 1`;
echo $value;
done < "myfile"

echo $value;

Note: This example just counts the number of lines, I actually desire to do more complex processing than this though, so 'wc' is not an alternative, nor is perl im afraid.

Thanks Darren.

most of the problems i need to solve doesn't involve the use of loops at all. sometimes, using while loops sometime could be slower than just using tools like awk.
if you want to do more complex processing, why not try awk.

Code:

awk '{
     # some processing with file
     }
END { print "number of lines is " NR }' file

dpoper1 · 04-28-2008, 03:05 PM

hi,

I am trying to do a loop, the main puporse of the loop is that it will search in a multiple text files stored on tmp2 a pattern /remote-host so it would output the pattern into tmp3.

The code that I have is the following:

for i in $( tmp2 ) ; do
sed -n '/remote-host/p' tmp2 >> tmp3
done

and obviously is not working, I would appreciate any help.

regards,

mike

lbt · 08-10-2009, 07:39 AM

A simple solution to the subject line:

cat file |
(
while read line
do
echo process $line
done
)

ghostdog74 · 08-10-2009, 08:47 AM

you are digging up an old thread. check the date of post next time. also, no need to use cat. its useless

lbt · 08-10-2009, 09:14 AM

Quote:

Originally Posted by ghostdog74

you are digging up an old thread. check the date of post next time. also, no need to use cat. its useless

The only reason I posted is because such an old thread was the top search result on google and had no answers that a new user could, IMHO, understand.

Using cat rather than a redirect here (again IMO) makes the answer crystal clear and hopefully will educate rather than confuse

Code:

(
  while read line
  do
    echo process $line
  done
) < file

does work but it isn't clear as you start to read the code without realising that, potentially many lines later, a file will be directed into the sub shell.

If you are after an optimised solution feel free to use exec with a fd numeric redirect and read -u too :

Code:

exec 9<file
while read -u9 line
do
  echo process $line
done

Explanation left as an exercise for the reader...