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< h2 id = "characterswithspecialmeaning" > Characters with special meaning< / h2 >
< p > We have seen that, we are using < code > *< / code > , < code > +< / code > , < code > .< / code > , < code > $< / code > , etc for different purposes. Now, if we want to match them themselves, we have to escape them using escape character(backslash-\) .< / p >
< p > Below is the table for these kind of characters and their escaped version, along with their usages.< / p >
< table >
< tr >
< td > Character< / td >
< td > Usage< / td >
< td > Escaped version< / td >
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< / tr >
< tr >
< td > \< / td >
< td > escape character< / td >
< td > \\< / td >
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< / tr >
< tr >
< td > .< / td >
< td > predefined character class< / td >
< td > \.< / td >
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< / tr >
< tr >
< td > |< / td >
< td > OR operator< / td >
< td > \\< / td >
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< / tr >
< tr >
< td > *< / td >
< td > as quantifier< / td >
< td > \*< / td >
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< / tr >
< tr >
< td > +< / td >
< td > as quantifier< / td >
< td > \+< / td >
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< / tr >
< tr >
< td > ?< / td >
< td > as quantifier< / td >
< td > \?< / td >
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< / tr >
< tr >
< td > ^< / td >
< td > boundary matcher< / td >
< td > \^< / td >
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< / tr >
< tr >
< td > $< / td >
< td > boundary matcher< / td >
< td > \$< / td >
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< / tr >
< tr >
< td > {< / td >
< td > in quantifier notation< / td >
< td > \{< / td >
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< / tr >
< tr >
< td > }< / td >
< td > in quantifier notation< / td >
< td > \}< / td >
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< / tr >
< tr >
< td > [< / td >
< td > in character class notation< / td >
< td > \[< / td >
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< / tr >
< tr >
< td > ]< / td >
< td > in character class notation< / td >
< td > \]< / td >
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< / tr >
< tr >
< td > (< / td >
< td > in group notation< / td >
< td > \(< / td >
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< / tr >
< tr >
< td > )< / td >
< td > in group notation< / td >
< td > \)< / td >
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< / tr >
< tr >
< td > -< / td >
< td > range operator< / td >
< td > NA< / td >
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< / tr >
< / table >
< p > Sometimes, it is also preferred to use escaped forward slash(< code > /< / code > ).< / p >
< h2 id = "bonusproblems" > Bonus Problems< / h2 >
< ol >
< li > < p > Predict the output of the following regex:< / p >
< p > < strong > RegEx:< / strong > < code > \b(0|(1(01*0)*1))*\b< / code > < br >
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< strong > Text:< / strong > < code > This RegEx denotes the set of binary numbers divisible by 3:
0,11,1010, 1100, 1111, 1001< / code > < / p >
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< p > Answer: < / p >
< div class = "container" >
< iframe scrolling = "no" style = "position: absolute; top: -9999em; visibility: hidden;" onload = "this.style.position='static'; this.style.visibility='visible';" src = "https://regexr.com/4vtqu" class = "embed" > < / iframe >
< / div > < / li >
< li > < p > Find a regular expression to match whole lines in the text containing either Apple, Orange, Grape as a word.< / p >
< p > Hint: Use < code > ^< / code > and < code > $< / code > to match whole lines.< / p >
< p > Answer: < code > ^.*\b(apple|orange|grape)\b.*$< / code > < / p >
< div class = "container" >
< iframe scrolling = "no" style = "position: absolute; top: -9999em; visibility: hidden;" onload = "this.style.position='static'; this.style.visibility='visible';" src = "https://regexr.com/4vtra" class = "embed" > < / iframe >
< / div > < / li >
< li > < p > Find an expression which matches < code > cat.< / code > , < code > 896.< / code > , < code > ?=++< / code > but not < code > abc1< / code > .< / p >
< p > Answer: < code > ...\W< / code > < / p >
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< iframe scrolling = "no" style = "position: absolute; top: -9999em; visibility: hidden;" onload = "this.style.position='static'; this.style.visibility='visible';" src = "https://regexr.com/4vu8e" class = "embed" > < / iframe >
< / div > < / li >
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