Using regex with grep

One of my homework questions is to search using grep an lines that contain the word 'death' or 'breath'.

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I know the [] operator acts as an or, but how do I use it to specify 'd' or 'br' ?

This won't work:

egrep [dbr]eath test_file

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(d|br) is for either d or br.

The square brackets are for matching a single character from square brackets.

For example: [asdf]ello would match aello, sello, dello, or fello.

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egrep '(d|br)eath' test_file

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The "|" operator (vertical bar) acts as an "or". However:

grep 'breath|death' test_file

What you wrote would find "death", "beath", and "reath".

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Study up on "alternation" and you'll figure it out.

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egrep is FYI, deprecated. Use grep -E

grep -E '(d|br)eath' file