1
00:00:01,210 --> 00:00:02,580
- [Instructor] Now that we've introduced

2
00:00:02,580 --> 00:00:04,620
the asterisk quantifier,

3
00:00:04,620 --> 00:00:08,170
which says zero or more occurrences

4
00:00:08,170 --> 00:00:12,380
of whatever regular expression
character precedes it,

5
00:00:12,380 --> 00:00:15,400
let's talk about some
of the other quantifiers

6
00:00:15,400 --> 00:00:16,950
that are available to us.

7
00:00:16,950 --> 00:00:19,310
So, of course, asterisk is zero or more

8
00:00:19,310 --> 00:00:21,070
but what if you wanted to guarantee

9
00:00:21,070 --> 00:00:25,140
there is at least one of
a particular character?

10
00:00:25,140 --> 00:00:29,905
Well, in that case, we can
use the plus quantifier.

11
00:00:29,905 --> 00:00:34,740
So, here we have the expression,
the regular expression,

12
00:00:34,740 --> 00:00:37,576
that's going to look for
a capital first letter

13
00:00:37,576 --> 00:00:42,100
followed by at least one lowercase letter.

14
00:00:42,100 --> 00:00:45,100
So, of course, Wally has
a capital first letter

15
00:00:45,100 --> 00:00:47,330
and at least one lowercase letter

16
00:00:47,330 --> 00:00:49,690
and that does indeed match.

17
00:00:49,690 --> 00:00:52,740
On the other hand, if I were to go ahead

18
00:00:52,740 --> 00:00:56,323
and change this to a capital E,

19
00:00:57,880 --> 00:01:00,364
now, that is going to match this piece,

20
00:01:00,364 --> 00:01:04,950
but there is not at least one
lowercase letter following it,

21
00:01:04,950 --> 00:01:07,500
so, in that case, we get invalid

22
00:01:07,500 --> 00:01:09,880
because it's not matching the result,

23
00:01:09,880 --> 00:01:11,670
so we did valid and invalid

24
00:01:11,670 --> 00:01:14,280
in this particular demonstration.

25
00:01:14,280 --> 00:01:16,940
Now, there are some other
quantifiers, as well,

26
00:01:16,940 --> 00:01:19,467
and we're going to demonstrate those here.

27
00:01:19,467 --> 00:01:22,070
By the way, I should
mention before I do that,

28
00:01:22,070 --> 00:01:25,604
the plus quantifier and
the asterisk quantifier

29
00:01:25,604 --> 00:01:28,490
are what we call greedy quantifiers,

30
00:01:28,490 --> 00:01:32,090
which means they're going
to match as many characters

31
00:01:32,090 --> 00:01:34,604
as they possibly can, by default.

32
00:01:34,604 --> 00:01:38,600
All right, let's talk about a quantifier

33
00:01:38,600 --> 00:01:43,600
that matches zero or one
occurrence of a sub-expression

34
00:01:44,240 --> 00:01:46,220
within a regular expression.

35
00:01:46,220 --> 00:01:49,170
So, let me go ahead and copy
and paste in the next one.

36
00:01:49,170 --> 00:01:50,550
Actually, you know what, let's go ahead

37
00:01:50,550 --> 00:01:53,440
and percent-clear this so that we can work

38
00:01:53,440 --> 00:01:55,013
from the top of the screen here.

39
00:01:55,013 --> 00:01:58,280
So, this is the question mark quantifier

40
00:01:58,280 --> 00:02:02,280
and it's going to match
zero or one occurrence

41
00:02:02,280 --> 00:02:05,330
of the sub-expression that precedes it,

42
00:02:05,330 --> 00:02:08,460
which, in this case, is a literal l.

43
00:02:08,460 --> 00:02:10,240
So, what we're doing here is creating

44
00:02:10,240 --> 00:02:12,610
a regular expression that's capable,

45
00:02:12,610 --> 00:02:15,660
for example, of matching
both the US English

46
00:02:15,660 --> 00:02:19,690
and the UK English spellings
of the word labeled.

47
00:02:19,690 --> 00:02:23,132
So this will match one or two l's in a row

48
00:02:23,132 --> 00:02:25,890
but it would not match zero l's

49
00:02:25,890 --> 00:02:27,530
and it would not match three l's

50
00:02:27,530 --> 00:02:31,360
which would be incorrectly
spelled words in that case.

51
00:02:31,360 --> 00:02:34,093
So, we do indeed get a match there.

52
00:02:35,470 --> 00:02:38,060
On the other hand, actually
not on the other hand,

53
00:02:38,060 --> 00:02:39,900
in this case, let's do it again.

54
00:02:39,900 --> 00:02:43,290
So, we used two l's in
this one and that matched

55
00:02:43,290 --> 00:02:46,170
but we want to show that it
will work with one l as well,

56
00:02:46,170 --> 00:02:48,470
so, again, we still get the match there.

57
00:02:48,470 --> 00:02:51,680
On the other hand now, if I do three l's

58
00:02:51,680 --> 00:02:53,630
in the string that we're searching,

59
00:02:53,630 --> 00:02:56,010
that will not match because this says

60
00:02:56,010 --> 00:02:59,810
I only want zero or one of the character

61
00:02:59,810 --> 00:03:02,090
that precedes the question mark.

62
00:03:02,090 --> 00:03:03,890
So, let's go ahead and execute that,

63
00:03:03,890 --> 00:03:07,179
and indeed, we can see
that we get no match.

64
00:03:07,179 --> 00:03:11,462
Now, you can also specify a quantifier

65
00:03:11,462 --> 00:03:14,976
that's for a range of values.

66
00:03:14,976 --> 00:03:18,970
You can do it for at least
a specific number of items

67
00:03:18,970 --> 00:03:23,970
or between a starting
and ending value as well.

68
00:03:24,250 --> 00:03:26,820
So let's do at least first.

69
00:03:26,820 --> 00:03:30,120
So here we have a regular expression

70
00:03:30,120 --> 00:03:32,530
with a quantifier that says I would like

71
00:03:32,530 --> 00:03:35,200
at least three digits in a row.

72
00:03:35,200 --> 00:03:39,080
So backslash d is the
character class for digits

73
00:03:39,080 --> 00:03:42,730
and three comma inside of curly braces

74
00:03:42,730 --> 00:03:46,120
says I want three or more digits in a row.

75
00:03:46,120 --> 00:03:48,580
Now, of course, we have
exactly three digits

76
00:03:48,580 --> 00:03:51,320
right here so I'll go
ahead and execute that

77
00:03:51,320 --> 00:03:54,040
and we do get match as a result

78
00:03:54,040 --> 00:03:56,470
and let's do it with more digits

79
00:03:56,470 --> 00:03:59,470
so same regular expression,
lots more digits,

80
00:03:59,470 --> 00:04:01,090
we still have a match,

81
00:04:01,090 --> 00:04:04,000
but if I do that same thing once again,

82
00:04:04,000 --> 00:04:08,670
and let's say, this time we
cut it down to only two digits,

83
00:04:08,670 --> 00:04:13,190
now we get no match because
it's looking for at least three.

84
00:04:13,190 --> 00:04:17,340
Now, you can also do a
closed range of values.

85
00:04:17,340 --> 00:04:20,590
So, for example, here we
are saying we would like

86
00:04:20,590 --> 00:04:25,260
consecutive digits of either three, up to,

87
00:04:25,260 --> 00:04:28,130
of three up to but, and including,

88
00:04:28,130 --> 00:04:30,840
up to and including six
total digits in a row.

89
00:04:30,840 --> 00:04:33,710
So, somewhere between three and six digits

90
00:04:33,710 --> 00:04:36,730
will match this particular
regular expression.

91
00:04:36,730 --> 00:04:38,960
So, three certainly does match

92
00:04:38,960 --> 00:04:42,850
and we'll do six next
to test the other end,

93
00:04:42,850 --> 00:04:45,870
so that matched, but if I
go ahead and modify that,

94
00:04:45,870 --> 00:04:48,030
and let's make that a seven,

95
00:04:48,030 --> 00:04:50,290
so that we have seven digits in a row,

96
00:04:50,290 --> 00:04:52,763
now we have no further match.