CODEWITHSUNDEEP
regexlinuxgrep
LZh
LZh

Reputation: 103

Regex getting dot files except the current and parent dictionaries

I'm reading the book "How Linux Works". The author gave the following regular expressions so I can get all dot files except the current and parent directories. (Page 21)

.??*
.[^.]*

If any dot files exist in the directory the both work. But when no dot files exist only the first one work.

I can't understand them. Can you describe me?

$ ls -a
. .. .hiding something

$ ls -a | grep .??*
.hiding

$ ls -a | grep .[^.]*
.hiding

$ mv .hiding hiding

$ ls -a | grep .??*

$ ls -a | grep .[^.]*
.
..
hiding
something

Upvotes: 2

Views: 278

Answers (1)

ntki
ntki

Reputation: 2314

The first does not really make sense, does not work for me, and I cannot find any documentation about ?? either.

Regardless, there are two problems with both of these regexes:

  1. The . here matches any char. In order to match only for a single dot as it is, you have to put a \ in front of it, like \..

  2. The whole expression can match anywhere in the line. You have to assert that the matching starts at the beginning. So start with ^.

Try: ls -a | grep '^\.[^.]' This means: starting at the beginning of the line, find a single dot. Then any char that is not listed (negation is done by the second ^ here) between the brackets, so not a literal dot.

In brackets you don't have to use \, although you can.

Upvotes: 2

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