What does this ($\d\d\d$\s)? regex match?

Question

What does this ((\d\d\d)\s)? regex match?

You have two different expressions in the title and the question. Pick one. — Mad Physicist, Mar 05 '18 at 05:56
Possible duplicate of [Meaning of regular expressions like - \\d , \\D, ^ , $ etc](https://stackoverflow.com/questions/36982512/meaning-of-regular-expressions-like-d-d-etc) — Abdulla Nilam, Mar 05 '18 at 05:56
and https://stackoverflow.com/questions/22937618/reference-what-does-this-regex-mean — Abdulla Nilam, Mar 05 '18 at 05:56
The regex in the header and description is different, which one are you interested to know. — Hassan Imam, Mar 05 '18 at 05:56
Another example, \\d. This regex does not accept a single digit, say 5. How different is it from \d? @TimBiegeleisen — Moses Kirathe, Mar 05 '18 at 06:01
`($\d\d\d$\s)?` means do a non-greedy regex search for 3 digits inside parenthesis followed by a space. — Hassan Imam, Mar 05 '18 at 06:03
Originally, a backslash always escaped any character, so `\.` matches a literal dot, `\[` matches an opening square bracket, etc. At some point, shorthands like `\t` (tab) were loaned from C, and then the floodgates were open. In Perl-style regex, *generally* a backslash before an alphabetic represents a character class, while backslashes before punctuation quotes it. A backslash before a backslash, of course, also quotes it, so `\\ ` (still) matches a literal backslash. — tripleee, Mar 05 '18 at 06:31

score 1 · Answer 1 · answered Mar 05 '18 at 06:01

\d matches the digits. it is all about the langugae you are using. In python3, [0-9] matches only 0123456789 characters, while \d matches [0-9] and other digit characters, for example Eastern Arabic numerals ٠١٢٣٤٥٦٧٨٩.

\s matches any whitespace character

score 1 · Answer 2 · answered Mar 05 '18 at 06:15

\d matches digits from [0-9].

\s matches white-space characters like [ \t\n\r]

? is means optional, it matches even if the following regex are not present.

() are used for grouping.

Now the question is what does ((\d\d\d)\s)? match? \d\d\d matches 3 consecutive digits and group them to $1.

((\d\d\d)\s) matches 3 consecutive followed by space and this is grouped to $2.

since we have ? at the end of the regex, it matches digits followed with space and also if there are no such match.

In case if there is no match, it points to start of the line.

score 1 · Accepted Answer · answered Mar 05 '18 at 06:27

1

The regex expression :

The first backslash escapes the open parenthesis that follows, as it is a special character, so the regex will search for an open and a close parenthesis in the input string

Example : (111)

answered Mar 05 '18 at 06:27

Moses Kirathe

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score 0 · Answer 4 · answered Mar 05 '18 at 05:58

have a look at this site https://regex101.com/r/yS5fU8/2

1st Capturing Group (\d\d\d)

p (\d\d\d) \d matches a digit (equal to [0-9])
\d matches a digit (equal to [0-9])
\d matches a digit (equal to [0-9])
\d matches a digit (equal to [0-9])

and - \s matches any whitespace character (equal to [\r\n\t\f\v ])

What does this (\(\d\d\d\)\s)? regex match?

4 Answers4