UNIX Command Line

On one of my directory I had a lot of log files and I had to find the count of the total number of lines which starts with 's' (i.e. ^s).
My first approach was:

$ ls | xargs -i grep -c ^s {} | awk '{sum+=$0} END {print sum}'
190978

And I got my result. Then I thought of performing the same using bash scripting for and while loop and this is what I tried.

#!/bin/sh

sum=0
DIR=~/original
for file in $(ls $DIR)
  do
      Slines=$(grep -c ^s $DIR/$file)
      ((sum+=Slines))
      #You can also use
      #sum=$(expr $sum + $Slines)
      #sum=`expr $sum + $Slines`
done
echo $sum

Executing it:

$ ./usingfor.sh
190978

Cool, correct result.

And then I modified the above script for bash while loop:

#!/bin/sh
sum=0
DIR=~/original
ls $DIR | while read file
  do
      Slines=$(grep -c ^s $DIR/$file)
      ((sum+=Slines))
done
echo $sum

Executing it:

$ ./usingwhile.sh
0

Oops!!! what went wrong ?

In Bash shell, piping directly to bash while loop causes the bash shell to function in a sub shell.
So in the above example the scope of the 'sum' variable is limited to the sub-shell of the while loop and so the modified value of 'sum' is not reflected when we exit the loop. Value of sum is still 0 (local value) as we initialized it to 0 at the beginning of the script.

The solution of this variable scoping problem with while and direct piping will be:

Remove the direct pipe and feed the list of file names under '~/original' directory as stdin to the while loop as shown below (Basically create a temp file with the file names of the directory '~/original')

#!/bin/sh
sum=0
DIR=~/original
ls $DIR > /tmp/filelist

while read file
  do
      Slines=$(grep -c ^s $DIR/$file)
      ((sum+=Slines))
done < /tmp/filelist
echo $sum

Executing it:

$ ./usingwhile_1.sh
190978

And the result is correct.