Question

I’m sure I’m doing something really obviously wrong here, but I can’t figure out what. Using grep from a bash shell, I have a file test.txt:

ABC123
ABC456
ABC789
DEF123
DEF456
DEF789

Now at the command line:

$ grep ABC test2.txt
ABC123
ABC456
ABC789

$ grep DEF test2.txt
DEF123
DEF456
DEF789

So those work great. Now, I expect the following command to print the whole file, but:

$ grep ABC\|DEF test2.txt

$ grep (ABC)\|(DEF) test2.txt
-bash: syntax error near unexpected token `ABC'

$ grep \(ABC\)\|\(DEF\) test2.txt

$ grep 'ABC|DEF' test2.txt

What am I doing wrong?

Answer 1

Turn on the extended regex with -E:

grep -E "ABC|DEF" test2.txt