check if a string starts with number using regular expression

Question

I am writing a filebeat configuration when I am matching if a line starts with a number like 03:32:33 ( a timestamp). I am currently doing it by-

\d

But its not getting recognised, is there anything else which I should do. I am not particularly good/ have experience with regex. Help will be appreciated.

Answer 1

The real problem is that filebeat does not support \d.

Replace \d by [0-9] and your regular expression will work.

I suggest you to give a look at the filebeat's Supported Patterns.

Also, be sure you've used ^, it stands for the start of the string.

Answer 2

Regex: (^\d)

1st Capturing group (^\d)
    ^ Match at the start of the string
    \d match a digit [0-9] 

Answer 3

You can use this regex:

^([0-9]{2}:?){3}

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DEMO

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Assert position at the beginning of the string «^»
Match the regex below and capture its match into backreference number 1 «([0-9]{2}:?){3}»
   Exactly 3 times «{3}»
      You repeated the capturing group itself.  The group will capture only the last iteration.  Put a capturing group around the repeated group to capture all iterations. «{3}»
      Or, if you don’t want to capture anything, replace the capturing group with a non-capturing group to make your regex more efficient.
   Match a single character in the range between “0” and “9” «[0-9]{2}»
      Exactly 2 times «{2}»
   Match the character “:” literally «:?»
      Between zero and one times, as many times as possible, giving back as needed (greedy) «?»

Answer 4

You can use:

^\d{2}:\d{2}:\d{2}

The character ^ matches the start of a line.