grep: problem with regular expression

Question

Can anyone explain why this does not work?

grep -ne '[A-Za-z]{1,30}\ [A-Z][a-z]{1,30}\W[A-Za-z]{1,30}\ [0-9]{1,30}\W[0-9]{5}\ [A-Za-z]{1,30}(\ [A-Za-z]{1,30})?' emails

(possibly) Related: https://unix.stackexchange.com/questions/194912/what-is-the-email-matching-regex-in-basic-regex-for-grep — Kusalananda, Apr 28 '17 at 07:09
For one, because the `{n,m}` needs extended regular expressions (`grep -E`) or backslashes. See: [here](https://unix.stackexchange.com/questions/119905/why-does-my-regular-expression-work-in-x-but-not-in-y) and grep's man page too — ilkkachu, Apr 28 '17 at 07:15

score 3 · Answer 1 · edited Apr 28 '17 at 10:47

3

First, you are using extended regular expression (ERE) syntax like {}, () and ?. Add option -E to use ERE or do escape {} and () with backslashes and replace ? like this: grep -ne '[A-Za-z]\{1,30\} [A-Z][a-z]\{1,30\}\W[A-Za-z]\{1,30\} [0-9]\{1,30\}\W[0-9]\{5\} [A-Za-z]\{1,30\}\( [A-Za-z]\{1,30\}\)\{0,1\}' emails

Second, you are escaping spaces with backslashes inside single quotes. While most implementations of grep will handle this as simple spaces, the posix standard considers this undefined: The interpretation of an ordinary character preceded by a backslash ( '\' ) is undefined.

There may be additional problems, but we can't know without knowing the syntax of your file and what you want to grep

edited Apr 28 '17 at 10:47

Stéphane Chazelas

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answered Apr 28 '17 at 08:08

Philippos

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`[A-Z]` is also undefined other than in the `C`/`POSIX` locale per posix. In practice, it generally matches more characters (even possibly collating sequences made of more than one character) than the 26 letters of the english alphabet. – Stéphane Chazelas Apr 28 '17 at 10:49
Given that the pattern is not anchored, the `\( [A-Za-z]\{1,30\}\)\{0,1\}` is also superfluous. Possibly `-x` is missing. – Stéphane Chazelas Apr 28 '17 at 10:51

grep: problem with regular expression

1 Answers1