You need to check a configuration option or command-line
response for a positive value. You want to provide some flexibility in the accepted
responses, so that true
, t
, yes
, y
, okay
, ok
, and 1
are all accepted in any combination
of uppercase and lowercase.
Using a regex that combines all of the accepted forms allows you to perform the check with one simple test.
^(?:1|t(?:rue)?|y(?:es)?|ok(?:ay)?)$
Regex options: Case insensitive |
Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby |
The following breakdown shows the individual parts of the regex. Combinations of tokens that are easy to read together are shown on the same line:
^ # Assert position at the beginning of the string. (?: # Group but don't capture... 1 # Match a literal "1". | # or... t(?:rue)? # Match "t", optionally followed by "rue". | # or... y(?:es)? # Match "y", optionally followed by "es". | # or... ok(?:ay)? # Match "ok", optionally followed by "ay". ) # End the noncapturing group. $ # Assert position at the end of the string.
Regex options: Case insensitive, free-spacing |
Regex flavors: .NET, Java, PCRE, Perl, Python, Ruby |
This regex is essentially a simple test for one of seven
literal, case-insensitive values. It could be written in a number of
ways. For example, ‹^(?:[1ty]|true|yes|ok(?:ay)?)$
› is an equally
good approach. Simply alternating between all seven values as ‹^(?:1|t|true|y|yes|ok|okay)$
›
would also work fine, although for performance reasons it’s generally
better to reduce the amount of alternation via the pipe ‹|
› operator in favor of
character classes and optional suffixes (using the ‹?
› quantifier). In this case,
the performance difference is probably no more than a few
microseconds, but it’s a good idea to keep regex performance issues in
the back of your mind. Sometimes the difference between these
approaches can surprise you.
All of these examples surround the potential match values with a
noncapturing group to limit the reach of the alternation operators. If
we omit the grouping and instead use something like ‹^true|yes$
›, the regex engine
will search for “the start of the string followed by ‘true’” or “‘yes’
followed by the end of the string.” ‹^(?:true|yes)$
› tells the regex engine to find
the start of the string, then either “true” or “yes”, and then the end
of the string.
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