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Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
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It's marked solved, but since OP didn't post the solution:
-e uses basic regular expressions, where you need to escape the meta-characters ((|)) with a backslash. Alternatively, use extended regex with -E
$ echo a | grep -E "(a|b)"
a
$ echo a | grep -e "\(a\|b\)"
a
$ echo a | grep -e "(a|b)"
$ echo a | grep -E "\(a\|b\)"
Do you get output if you use that exact tail command without the grep pipe?
Yes