1. Regular Expressions

2. Where can I use Powerful in Text Editors – vi, editplus
- Search , search and replace, text processing
Text Editors – vi, editplus
Programming languages - perl, Java
Grep,awk
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3. Before RegEx Wildcard *.txt My_report*.doc
Here the * indicates any number of any characters.
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4. !
Regular expressions (RegEx) tend to be easier to write than they are to read
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5. What is RegEx
a regular expression-- a pattern that describes or matches a set of strings
Matched text– chunk of text which matches the regular expression.
ca[trn]
Matches car, can, cat
Editplus is used throughout this presentation as tool to demonstrate the regular expressions
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6. Structure of RegEx Made up of normal characters and metacharacters.
Metacharacters – special function
$ ^ . \ [] \( \) + ?
$ means end of line
^ start of line
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7. Literal match RegEx: cat will match the word cat
It will also match words like concatenation , delicate, located, modification
It is not desired sometimes ?
solution
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8. Matching Match the space before and after “cat” “ cat ”
? Still problem
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9. Character class Want to search ‘in’ or ‘on’ ..
So searching RegEx : [io]n will match in and on both
[ ] : used to specify a set of character to select from.
[a-h] : indicates set of all characters from a to h
[4-9A-T]
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10. Character class
It can also contain individual characters as : [acV5y0]
[0-9] : ?
[0-9][0-9] :?
18[0-9][0-9]:?
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11. Example set of vowels set of consonents
[aeiou]
set of consonents
[bcdfghjklmnpqrstvwxyz]
Consider matching words which start with 2 vowels and end with consonant
[aeiou][aeiou][bcdfghjklmnpqrstvwxyz] ?
“ [aeiou][aeiou][bcdfghjklmnpqrstvwxyz] ”
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12. Negation
The absence of any character or set of character can be shown using ^ symbol
[^ab^8] : means not a , but b , but not 8
[^c-p] : means any character other than c..p
“[^t]ion ” : select all words ending with ion but with not before it
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13. Start/End of line ^ : indicates start of line
$ : indicates end of line
Example:
search lines starting with I
Use RegEx : “^I ”
search lines ending ending with is
Use RegEx : “ is$”
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14. match . : Any character match
e.e : match all strings where first letter is e and last is e.
Try “ e.e ”
If you want only words to be searched then change the query to
e[a-z]e
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15. Repeated match
* : match the previous character or character-class zero or more times
be* : will match sequence of zero or more ‘e’ preceded by b
+ : similar to *
Only difference is that it matches sequence of one or more.
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16. Selecting a number Single digit : [0-9]
When single digit is repeated zero or more times it is a number.
(digit)repeat
[0-9]*
$[0-9]* : ?
\$[0-9]*
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17. Selecting a word Word is composed of alphabets A word is : [a-z]*
A word in all capital letters : ??
A word starting with capital letter :[ ][ ]*
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18. Alternate match | : symbol is used to specify alternate match
Search: (above)|(below)
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19. Search Day Words [a-z]*day “[a-z]+day ” - “[A-Z][a-z]+day ”
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20. Escaping Special meaning
How to match (, ) or *
To match the characters which are used as Metacharacter, ‘\’ is added before them as an escape character.
i.e. to match ( write \( and to match period . write \.
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21. Search patterns has, have, had not, n’t ((have)|(had)|(has))
(( )|(n't)|( not ))*
((have)|(had)|(has))(( )|(n't)|( not ))*
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23. References Editplus help pages
OReilly - Mastering Regular Expressions
Google “regular expression tutorial”
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24. Thank you !
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