Regex- First instance of Time in a string - regex

Question

I am trying to build a regular expression that would pull the first time out of a string.
The issue is the time format is not standardized.
Here are the possible variations.
':' with 1 hour digit before the ':' (ex. 9:00 pm)
':' with 2 hour digits before the ':' (ex. 10:00pm)
no minutes with with 1 hour digit (ex 9pm)
no minutes with with 1 hour digit (ex 10pm)
Additionally there may or may not be a space before "am" or "pm"
Here is an example string.
7:30 pm -9 pm Lorem Ipsum is simply dummy text. 9pm-10pm Lorem Ipsum is simply dummy text
I would like this string to return "7:30 pm"

Answer 1

You did not specify the tool you want to use, here a simple implementation using sed:
echo '7:30 pm -9 pm Lorem Ipsum is simply dummy text. 9pm-10pm Lorem Ipsum is simply dummy text' | sed 's/\([0-2]\?[0-9]\(:[0-5][0-9]\)\? *[ap]m\).*/\1/i'
Legenda:
'[0-2]\?[0-9]' match the hour (with 1 or 2 digits)
'\(:[0-5][0-9]\)\?' match the minutes (optional)
' *' optional spaces
'[ap]m' match am,pm,AM,PM (also Am,aM,pM,Pm)*
'.*' match all the rest of the string
In addiction: the external \(...\) create a group of all the above elements (a backreference) used later in the substitution part of the regex \1.
*: The last /i modifier make the regex case insensitive
You can rewrite all as a standard perl regex:
/(?i)[0-2]?\d(?::[0-5]\d)?\s*[ap]m/
Little ruby code:
#!/usr/bin/env ruby
input = "7:30 pm -9 pm Lorem Ipsum is simply dummy text. 9pm-10pm Lorem Ipsum is simply dummy text"
puts input[/(?i)[0-2]?\d(?::[0-5]\d)?\s*[ap]m/]

Answer 2

Try this regex:
(?i)\d{1,2}(?::\d{2})?\s*[ap]m
Explaining:
(?i) # insensitive case
\d{1,2} # one or two digits
(?: # optional group
:\d{2} # the minutes
)? # end optional group
\s* # any spaces
[ap]m # "am" or "pm"
Regex live here.
Hope it helps.

Answer 3

You can use the following regex:
\d{1,2}\:?(?:\d{1,2}|)\s*[ap]m

Answer 4

A almost generic solution may be achieved using following expression:
([012]?\d(:[0-5]\d)?\s*(pm|am|PM|AM))
It considers capturing groups, getting all present time strings on string.
In javascript, it might be tested like following:
var testTime = "7:30 pm -9 pm Lorem Ipsum is simply dummy text. 9pm-10pm Lorem Ipsum is simply dummy text";
var timeRex = /([012]?\d(:[0-5]\d)?\s*(pm|am|PM|AM))/g;
var firstTime = timeRex.exec(testTime)[0];
console.log(firstTime);
I really believe that there is a better general solution. I will try some more stable, then publish it here.