You want to match dates and/or times in the official ISO
8601 format, which is the basis for many standardized date and time
formats. For example, in XML Schema, the built-in date, time, and dateTime types are all based on ISO 8601.
The ISO 8601 standard defines a wide range of date and time formats. Most applications that use ISO 8601 only use a subset of it. These solutions match the most commonly used ISO 8601 date and time formats. We’ve also added solutions for XML Schema, which is one particular implementation of ISO 8601.
The following matches a calendar month (e.g., 2008-08). The hyphen is
required:
^([0-9]{4})-(1[0-2]|0[1-9])$| Regex options: None |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
Named capture makes the regular expression and any code that may reference the capturing groups easier to read:
^(?<year>[0-9]{4})-(?<month>1[0-2]|0[1-9])$| Regex options: None |
| Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9 |
Python uses a different syntax for named capture, adding a
P. For brevity, we only show one
solution using the Python syntax. All the other solutions using
.NET-style named capture can be easily adapted to Python-style named
capture in the same way.
^(?P<year>[0-9]{4})-(?P<month>1[0-2]|0[1-9])$| Regex options: None |
| Regex flavors: PCRE, Python |
ISO 8601 allows hyphens to be omitted from calendar dates, making both 2010-08-20 and 20100820 valid representations of the same date. The following regex accounts for this, but also allows for invalid formats like YYYY-MMDD and YYYYMM-DD.
^([0-9]{4})-?(1[0-2]|0[1-9])-?(3[01]|0[1-9]|[12][0-9])$| Regex options: None |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
^(?<year>[0-9]{4})-?(?<month>1[0-2]|0[1-9])-?↵
(?<day>3[01]|0[1-9]|[12][0-9])$| Regex options: None |
| Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9 |
Calendar date, such as 2008-08-30 or 20080830. The hyphens
are optional. This regex uses a capturing group and a backreference to
match YYYY-MM-DD or YYYYMMDD, but not YYYY-MMDD or YYYYMM-DD.
^([0-9]{4})(-?)(1[0-2]|0[1-9])\2(3[01]|0[1-9]|[12][0-9])$| Regex options: None |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
^(?<year>[0-9]{4})(?<hyphen>-?)(?<month>1[0-2]|0[1-9])↵
\k<hyphen>(?<day>3[01]|0[1-9]|[12][0-9])$| Regex options: None |
| Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9 |
Python also uses a different syntax for named backreferences:
^(?P<year>[0-9]{4})(?P<hyphen>-?)(?P<month>1[0-2]|0[1-9])↵
(?P=hyphen)(?<day>3[01]|0[1-9]|[12][0-9])$| Regex options: None |
| Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9 |
Ordinal date (e.g., 2008-243). The hyphen is
optional:
^([0-9]{4})-?(36[0-6]|3[0-5][0-9]|[12][0-9]{2}|0[1-9][0-9]|00[1-9])$| Regex options: None |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
^(?<year>[0-9]{4})-?↵
(?<day>36[0-6]|3[0-5][0-9]|[12][0-9]{2}|0[1-9][0-9]|00[1-9])$| Regex options: None |
| Regex flavors: .NET, Java 7, PCRE 7, Perl 5.10, Ruby 1.9 |
Week of the year (e.g., 2008-W35). The hyphen is
optional:
^([0-9]{4})-?W(5[0-3]|[1-4][0-9]|0[1-9])$| Regex options: None |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
^(?<year>[0-9]{4})-?W(?<week>5[0-3]|[1-4][0-9]|0[1-9])$| Regex options: None |
| Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9 |
Week date (e.g., 2008-W35-6). The hyphens are
optional.
^([0-9]{4})-?W(5[0-3]|[1-4][0-9]|0[1-9])-?([1-7])$| Regex options: None |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
^(?<year>[0-9]{4})-?W(?<week>5[0-3]|[1-4][0-9]|0[1-9])-?(?<day>[1-7])$| Regex options: None |
| Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9 |
Hours and minutes (e.g., 17:21). The colon is optional:
^(2[0-3]|[01][0-9]):?([0-5][0-9])$
| Regex options: None |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
^(?<hour>2[0-3]|[01][0-9]):?(?<minute>[0-5][0-9])$
| Regex options: None |
| Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9 |
Hours, minutes, and seconds (e.g., 17:21:59). The colons are
optional:
^(2[0-3]|[01][0-9]):?([0-5][0-9]):?([0-5][0-9])$
| Regex options: None |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
^(?<hour>2[0-3]|[01][0-9]):?(?<minute>[0-5][0-9]):?↵ (?<second>[0-5][0-9])$
| Regex options: None |
| Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9 |
Time zone designator (e.g., Z, +07 or +07:00). The colons and the minutes are
optional:
^(Z|[+-](?:2[0-3]|[01][0-9])(?::?(?:[0-5][0-9]))?)$
| Regex options: None |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
Hours, minutes, and seconds with time zone designator (e.g.,
17:21:59+07:00). All the colons are
optional. The minutes in the time zone designator are also
optional:
^(2[0-3]|[01][0-9]):?([0-5][0-9]):?([0-5][0-9])↵ (Z|[+-](?:2[0-3]|[01][0-9])(?::?(?:[0-5][0-9]))?)$
| Regex options: None |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
^(?<hour>2[0-3]|[01][0-9]):?(?<minute>[0-5][0-9]):?(?<second>[0-5][0-9])↵ (?<timezone>Z|[+-](?:2[0-3]|[01][0-9])(?::?(?:[0-5][0-9]))?)$
| Regex options: None |
| Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9 |
Calendar date with hours, minutes, and seconds (e.g.,
2008-08-30
17:21:59 or 20080830 172159). A space is required
between the date and the time. The hyphens and colons are optional.
This regex matches dates and times that specify some hyphens or colons
but omit others. This does not follow ISO 8601.
^([0-9]{4})-?(1[0-2]|0[1-9])-?(3[01]|0[1-9]|[12][0-9])↵
●(2[0-3]|[01][0-9]):?([0-5][0-9]):?([0-5][0-9])$| Regex options: None |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
^(?<year>[0-9]{4})-?(?<month>1[0-2]|0[1-9])-?↵
(?<day>3[01]|0[1-9]|[12][0-9])●(?<hour>2[0-3]|[01][0-9])↵
:?(?<minute>[0-5][0-9]):?(?<second>[0-5][0-9])$| Regex options: None |
| Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9 |
A more complicated solution is needed if we want to match date and time values that specify either all of the hyphens and colons, or none of them. The cleanest solution is to use conditionals. But only some flavors support conditionals.
^([0-9]{4})(-)?(1[0-2]|0[1-9])(?(2)-)(3[01]|0[1-9]|[12][0-9])↵
●(2[0-3]|[01][0-9])(?(2):)([0-5][0-9])(?(2):)([0-5][0-9])$| Regex options: None |
| Regex flavors: .NET, PCRE, Perl, Python |
^(?<year>[0-9]{4})(?<hyphen>-)?(?<month>1[0-2]|0[1-9])↵
(?(hyphen)-)(?<day>3[01]|0[1-9]|[12][0-9])●(?<hour>2[0-3]|[01][0-9])↵
(?(hyphen):)(?<minute>[0-5][0-9])(?(hyphen):)(?<second>[0-5][0-9])$| Regex options: None |
| Regex flavors: .NET, PCRE 7, Perl 5.10 |
^(?P<year>[0-9]{4})(?P<hyphen>-)?(?P<month>1[0-2]|0[1-9])↵
(?(hyphen)-)(?P<day>3[01]|0[1-9]|[12][0-9])●(?P<hour>2[0-3]|[01][0-9])↵
(?(hyphen):)(?P<minute>[0-5][0-9])(?(hyphen):)(?P<second>[0-5][0-9])$| Regex options: None |
| Regex flavors: PCRE, Perl 5.10, Python |
If conditionals are not available, then we have to use alternation to spell out the alternatives with and without delimiters.
^(?:([0-9]{4})-?(1[0-2]|0[1-9])-?(3[01]|0[1-9]|[12][0-9])↵
●(2[0-3]|[01][0-9]):?([0-5][0-9]):?([0-5][0-9])|↵
([0-9]{4})(1[0-2]|0[1-9])(3[01]|0[1-9]|[12][0-9])↵
●(2[0-3]|[01][0-9])([0-5][0-9])([0-5][0-9]))$| Regex options: None |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
The date and time types defined in the XML Schema
standard are based on the ISO 8601 standard. The date types allow
negative years for years before the start of the calendar (B.C.
years). It also allows for years with more than four digits, but not
for years with fewer than four digits. Years with more than four
digits must not have leading zeros. If you only want to allow years
with four digits as in the preceding solutions, remove -?(?:[1-9][0-9]*)? from the following
solutions.
Date, with optional time zone (e.g., 2008-08-30 or 2008-08-30+07:00).
Hyphens are required. This is the XML Schema date type:
^(-?(?:[1-9][0-9]*)?[0-9]{4})-(1[0-2]|0[1-9])-(3[01]|0[1-9]|[12][0-9])↵
(Z|[+-](?:2[0-3]|[01][0-9]):[0-5][0-9])?$| Regex options: None |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
^(?<year>-?(?:[1-9][0-9]*)?[0-9]{4})-(?<month>1[0-2]|0[1-9])-↵
(?<day>3[01]|0[1-9]|[12][0-9])↵
(?<timezone>Z|[+-](?:2[0-3]|[01][0-9]):[0-5][0-9])?$| Regex options: None |
| Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9 |
Time, with optional fractional seconds and time zone (e.g.,
01:45:36 or
01:45:36.123+07:00). There is no limit
on the number of digits for the fractional seconds. This is the XML
Schema time
type:
^(2[0-3]|[01][0-9]):([0-5][0-9]):([0-5][0-9])(\.[0-9]+)?↵ (Z|[+-](?:2[0-3]|[01][0-9]):[0-5][0-9])?$
| Regex options: None |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
^(?<hour>2[0-3]|[01][0-9]):(?<minute>[0-5][0-9]):(?<second>[0-5][0-9])↵ (?<frac>\.[0-9]+)?(?<timezone>Z|[+-](?:2[0-3]|[01][0-9]):[0-5][0-9])?$
| Regex options: None |
| Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9 |
Date and time, with optional fractional seconds and time zone
(e.g., 2008-08-30T01:45:36 or 2008-08-30T01:45:36.123Z). This is the
XML Schema dateTime
type:
^(-?(?:[1-9][0-9]*)?[0-9]{4})-(1[0-2]|0[1-9])-(3[01]|0[1-9]|[12][0-9])↵
T(2[0-3]|[01][0-9]):([0-5][0-9]):([0-5][0-9])(\.[0-9]+)?↵
(Z|[+-](?:2[0-3]|[01][0-9]):[0-5][0-9])?$| Regex options: None |
| Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
^(?<year>-?(?:[1-9][0-9]*)?[0-9]{4})-(?<month>1[0-2]|0[1-9])-↵
(?<day>3[01]|0[1-9]|[12][0-9])T(?<hour>2[0-3]|[01][0-9]):↵
(?<minute>[0-5][0-9]):(?<second>[0-5][0-9])(?<ms>\.[0-9]+)?↵
(?<timezone>Z|[+-](?:2[0-3]|[01][0-9]):[0-5][0-9])?$| Regex options: None |
| Regex flavors: .NET, Java 7, XRegExp, PCRE 7, Perl 5.10, Ruby 1.9 |
ISO 8601 defines a wide range of date and time formats. The
regular expressions presented here cover the most common formats, but
most systems that use ISO 8601 only use a subset. For example, in XML
Schema dates and times, the hyphens and colons are mandatory. To make
hyphens and colons mandatory, simply remove the question marks after
them. To disallow hyphens and colons, remove the hyphens and colons
along with the question mark that follows them. Do watch out for the
noncapturing groups, which use the ‹(?:⋯)› syntax. If a question mark and a colon
follow an opening parenthesis, those three characters open a
noncapturing group.
We put parentheses around all the number parts of the regexes. That makes it easy to retrieve the numbers for the years, months, days, hours, minutes, seconds, and time zones. Recipe 2.9 explains how parentheses create capturing groups. Recipe 3.9 explains how you can retrieve the text matched by those capturing groups in procedural code.
For most regexes, we also show an alternative using named capture.
Some of these date and time formats may be unfamiliar to you or your
fellow developers. Named capture makes the regex easier to understand.
.NET, Java 7, XRegExp, PCRE 7, Perl 5.10, and Ruby 1.9 support the
‹(?<› syntax used in the
solutions in this recipe. All versions of PCRE and Python covered in
this book support the alternative ‹name>⋯)(?P<› syntax, which adds a
‹name>⋯)P›. See Recipes 2.11 and 3.9
for details.
The number ranges in all the regexes are strict. For example, the calendar day is restricted between 01 and 31. You’ll never end up with day 32 or month 13. None of the regexes here attempts to exclude invalid day and month combinations, such as February 31st; Recipe 4.5 explains how you can deal with that.
The regular expressions, except those in the XML Schema
subsection, make the individual hyphens and colons optional. This does
not follow ISO 8601 exactly. For example, 1733:26 is not a valid ISO 8601 time, but
will be accepted by the time regexes. Requiring all hyphens and colons
to be present or omitted at the same time makes your regex quite a bit
more complex.
If the delimiters are all the same, we can do this quite
easily using a capturing group for the first delimiter and
backreferences for the remaining delimiters. The “dates” subsection of
the “Solution” section shows an example. For the first hyphen, we use
‹(-?)›, ‹(?<hyphen>-?)› or ‹(?P<hyphen>-?)› to match an
optional hyphen and capture it into a named or numbered group. If the
hyphen was omitted, the capturing group stores the zero-length string.
The question mark that makes the hyphen optional must be inside the
group. If we made the group itself optional, then backreferences to that
group would always fail to match if the hyphen was not matched, as the
group would not have participated in the match at all. For the remaining
hyphens, we use ‹\2›,
‹\k<hyphen>›, or
‹(?P=hyphen)› to match the
same text that was matched by the capturing group, which is either a
hyphen or nothing at all, depending on whether the first hyphen was
matched or not. When using numbered capture, make sure to use the
correct number for the backreference.
If the delimiters are different, such as when matching a single
string with both a date and a time, the solution is more complex. The
“date and time” subsection shows an example. This time, we use ‹(-)?›, ‹(?<hyphen>-)?› or ‹(?P<hyphen>-)?› to match the hyphen. Now the
question mark is outside the capturing group so that it will not
participate in the match at all when the hyphen is omitted. This allows
us to use the capturing group with a conditional. ‹(?(2)-)› matches a hyphen and
‹(?(2):)› matches a colon
if the second capturing group participated in the match. The
conditionals have no alternative, which means they will match nothing at
all (but still succeed) when the second capturing group did not
participate in the match. ‹(?(hyphen)-)› and ‹(?(hyphen):)› do the same using named
capture.
Only some flavors support conditionals. If conditionals are not available, the only solution is to use alternation to spell out the two alternatives with and without delimiters. The disadvantage of this solution is that it results in two capturing groups for each part of the date and time. Only one of the two sets of capturing groups will participate in the match. Code that uses this regex will have to check both groups.
This chapter has several other recipes for matching dates and times. Recipes 4.4 and 4.5 show how to validate traditional date formats. Recipe 4.6 shows how to validate traditional time formats.
Techniques used in the regular expressions in this recipe are discussed in Chapter 2. Recipe 2.3 explains character classes. Recipe 2.5 explains anchors. Recipe 2.8 explains alternation. Recipe 2.9 explains grouping. Recipe 2.10 explains backreferences. Recipe 2.11 explains named capturing groups. Recipe 2.12 explains repetition. Recipe 2.17 explains conditionals.
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