Question

For some mysterious reason, whenever I run grep from a “standalone” shell script as opposed to a simple function, the coloring of the output is not preserved.

Why is this happening and how can I prevent it?

This is best illustrated with an example:

Answer 1

You should try in your script :

grep --color

But please, no need to

echo `ls` |  grep ".txt"

just

ls -1 | grep --color ".txt"

or

printf '%s\n' | grep --color ".txt"

See http://porkmail.org/era/unix/award.html

EDIT

To change the defautl colors of grep, see man grep and search GREP_COLORS