I would like to extract specific lines from a file and output them into another file.

Each line in the file has a unique ID, and I have a specific list of IDs (that are not consecutive) that I wish to extract.

for example:

1 aaaaaa bbbcb cccccc
2 aaaaaa bbbbb cccccd
3 aaaaaa bbbab cccccc
4 aaaaaa bbbxb cccccc
5 aaaaaa bbbbb cwcccc
6 aaaaaa bbbbb cqcccc

I wish to extract only lines 3 and 5 of this file, how do I do this?

If the list of id-s is not very very very long, it could be as follows:

cat file | egrep "id1|id2|id3|...|idk"

cat file | egrep "^id1|^id2|^id3|...|^idk"