Find all lines in a file with a certain character at a certain position

Question

I have a lab question asking me to use grep with a regex pattern to match every word where the third letter from the beginning of the line is an "a" and save it with a redirect. How can I do that?

Answer 1

This should answer your question:

grep -e "^..a" < input > savefile

Answer 2

The solution proposed by @rahmu is simple if you look for low positions, but what if you look for the character number 25? Put in 25 dots?

In such a case the following solutions could be at hand. With grep

grep '^.\{24\}a' input >output

With awk

awk -F '' '$25 == "a"' input >output