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< h2 id = "practicalapplicationsofregex" > Practical Applications of RegEx< / h2 >
< ol >
< li > Syntax highlighting systems< / li >
< li > Data scraping and wrangling< / li >
< li > In find and replace facility of text editors< / li >
< / ol >
< p > Let's look at some classical examples of RegEx.< / p >
< h2 id = "numberranges" > Number Ranges< / h2 >
< p > Can you find a regex matching all integers from 0 to 255?< / p >
< p > First, Let's look at how can we match all integers from 0 to 59:< / 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/4vubt" class = "embed" > < / iframe >
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< p > As you can see, we have used < code > ?< / code > quantifier to make the first digit(0-5) optional. Now, can you solve it for 0-255?< / p >
< p > Hint : Use OR operator.< / p >
< p > We can divide the range 0-255 into three ranges: 0-199, 200-249 & 250-255. Now, creating an expression, for each of them independently, is easy.< / p >
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< td > Range< / td >
< td > RegEx< / td >
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< tr >
< td > 0-199< / td >
< td > [01][0-9][0-9]< / td >
< / tr >
< tr >
< td > 200-249< / td >
< td > 2[0-4][0-9]< / td >
< / tr >
< tr >
< td > 250-255< / td >
< td > 25[0-5]< / td >
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< p > Now, by using OR operator, we can match the whole 0-255 range.< / 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/4vuc0" class = "embed" > < / iframe >
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< p > As you can see, the above regex is not going to match 0, but 000. So, how can you modify the regex which matches 0 as well, rather than matching 001 only?< / 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/4vuc3" class = "embed" > < / iframe >
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< p > We have just used < code > ?< / code > quantifier.< / p >
< h2 id = "validateanipaddress" > Validate an IP address< / h2 >
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< p > IP address consists of digits from 0-255 and 3 points(< code > .< / code > ). Valid IP address format is < br > (0-255).(0-255).(0-255).(0-255).< / p >
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< p > For example, 10.10.11.4, 255.255.255.255, 234.9.64.43, 1.2.3.4 are Valid IP addresses.< / p >
< p > Can you find a regex to match an IP-address?< / p >
< p > We have already seen, how to match number ranges and to match a point, we use escaped-dot(< code > \.< / code > ). But in IP address, we don't allow leading zeroes in numbers like 001. < / p >
< p > So, We have to divide the range in four sub-ranges: 0-99, 100-199, 200-249, 250-255. And finally we use OR-operator.< / 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/4vuc9" class = "embed" > < / iframe >
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< p > So, Regex to match IP Address is as below:
< img src = "https://lh3.googleusercontent.com/n2CaC-8Q8NH-H5RkDrCM4AQQkV2PamIAlA3dwljdRsW33WWoj18qJEIN5iyzjLzfifHj-dh-IW-u=s1600" alt = "enter image description here" / > < / p >
< p > < strong > Note:< / strong > The whole expression is contiguous, for the shake of easy understanding it is shown the way it is.< / p >
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