Shell Programming and Scripting

Will someone give me an explanation on how the sed command below works.

Code:

sed 's/[.].*//'

Thanks!

Yes. On each line, sed deletes (substitutes nothing for) the leftmost dot (period) and the remainder of the line.

Code:

$ cat test.txt
.
abc.asfasfsadf
abc.abc.asfasdfa
abcabcddd

Code:

$ sed 's/[.].*//' test.txt

abc
abc
abcabcddd

Thanks. What does the right dot(period) and * mean and how is it seperated from the left period?

Sure. The right dot means "any single character", and * means "zero or more of preceding thing". So .* means "zero or more of any character". And each of the zero or more can be a different character. So .* matches the rest of the line after the first literal dot (literal period) on the line.

A* means "zero or more A".
.* means "zero or more ANY character".

You already know the left dot is inside the brackets, so is interpreted as a literal dot (literal period).

Oh, right dot is not separated from the left period. If it was separated, something different would happen.