Hi

Iam using grep command as follows in my script

read_file1()
{
cat file1.txt | while read line
do
grep $line file2.txt >> out.txt
done
}
read_file1

This way the performance is very slow. We are having lacks of records in file1 and file2

how can i improve the performance.

You can use the '-f' feature of the grep command to do this. I don't know how much faster it will be.

For example, if you have files named file1.txt and file2.txt (as in your example), then

grep -f file1.txt file2.txt >> out.txt

should do the job. Note that each line is a pattern.

No this command is not working.


what is pattern. hope my file is not a pattern

I'm not going to write the code for you, but what I think you want is to take advantage of "egrep" (or "grep -E" if gnu).

For example,

grep -E "one|two|three" yourfile

will find any of "one" "two" or "three" in "yourfile"

By the way, GNU grep has a lot of neat stuff: grep in depth