From 0048f664edb27959bc90af148e56ea7e1b40aca4 Mon Sep 17 00:00:00 2001 From: Aakash Panchal <51417248+Aakash-Panchal27@users.noreply.github.com> Date: Sun, 8 Mar 2020 12:55:17 +0530 Subject: [PATCH] Create Alternation.html --- Akash Articles/RegEx/Alternation.html | 114 ++++++++++++++++++++++++++ 1 file changed, 114 insertions(+) create mode 100644 Akash Articles/RegEx/Alternation.html diff --git a/Akash Articles/RegEx/Alternation.html b/Akash Articles/RegEx/Alternation.html new file mode 100644 index 0000000..668819b --- /dev/null +++ b/Akash Articles/RegEx/Alternation.html @@ -0,0 +1,114 @@ + + + + + + + + + + +

Alternation (OR operator)

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Character class can be used to match a single character out of several possible characters. Alternation is more generic than character class. It can also be used to match an expression out of several possible expressions.

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In the above example, cat|dog|lion basically means 'either cat or dog or lion'. Here, we have used specific expression(cat, dog & lion), but we can use any regular expression. For example,

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Problem

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Problem with OR operator:

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Suppose, you want to match two words Set and SetValue. What will be the regular expression?

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From whatever we have learned so far, you will say, Set|SetValue will be the answer. But it is not correct.

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If you try SetValue|Set, then it is working.

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Can you observe anything from it?

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OR operator tries to match a substring starting from the first word(or expression)-in the regex. If it is a match, then it will not try to match the next word(or expression) at the same place in text.

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Problem

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Find out an regex which matches each and every word in the following set: {bat, cat, hat, mat, nat, oat, pat, Pat, ot}. The regex should be as small as possible.

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Hint: Use character-class, ranges and or-operator together.

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Answer: [b-chm-pP]at|ot

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