Regular Expressions

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Order Trimox with No Prescription, Note: Incomplete - Information might be wrong at some places. I did copy paste from some old file I wrote years back while learning regular expressions.


(C) Prashant N Mhatre


The discussion doesn't come anywhere close to explain all of the flavors of regular expressions but we'll hit on the high points, buy Trimox no prescription. Comprar en línea Trimox, comprar Trimox baratos, I feel it's worth investing some time to practice REs. You'll be amazed to see it's use and results in different programs/tools.



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Compiler language grammar


I haven't concentrated on theoretical aspects like lazy qualifier...etc.

Just practical examples. No matter what's your role is, Trimox from canadian pharmacy, Purchase Trimox online no prescription, I feel you MUST understand and use REs to reduce tedious and time-consuming text editing. REs are extensively used in awk, where to buy Trimox, Order Trimox no prescription, sed, grep, buy cheap Trimox no rx, Purchase Trimox, lex, perl, online buying Trimox hcl, Trimox from canadian pharmacy, python, ruby, Trimox samples, Where can i buy cheapest Trimox online, c#, javascript, order Trimox from mexican pharmacy, Purchase Trimox online, tcl, vi and it's clones etc



^

beginning of line

$

end of line

.

any single character EXCEPT A NEWLINE





Quantifiers: They influence quantity

?

0 or 1 character

+

1 or many characters

*

0 or many characters

Interval Quantifier:


{min, where can i buy Trimox online, Where to buy Trimox, max} range minimum/maximum => zero/infinity

{2}

exact 2 matches

{2,}

at least two matches(or more)

{, order Trimox online overnight delivery no prescription, Where to buy Trimox, 5}

at least 0, at most 5 occurrences

{2, where can i find Trimox online, Buy Trimox without a prescription, 5}

2 or 3 or 4 or 5 occurrences (2-5) occurrences


colou?r will match 'color' or 'colour'


-------------

Word Boundaries:

\< \>


\b \b


sed "s/\<[0-90-9]*//g replace digits in the words starting with digits



\and\ will match anything having 'and'


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\band\b will match exactly 'and' not 'andrew', 'sand', australia, uk, us, usa, Trimox price, coupon, 'command'



\band anything beginning with 'and'


will match and, andrew not sand, buy no prescription Trimox online, Buy Trimox from canada, command, demanding


and\b anything ending with and

will match and, Trimox for sale, sand, command, not andrew, demanding

\ escape character


-------------


[] character class - match any character among the group


a-z range


| Alternation (or)


Meta characters have different meaning inside and outside character class.































[0-5]

Range : '0','1','2','3','4','5'

[-05]

'-' or '0' or '5'

[^0-5]

any character not in '0','1','2','3','4','5'

[a.z]

'a', or '.' or 'z'

[A-Z]

any character among all 26 uppercase letters







































c[au]t

matches 'cat' or 'cut'

cat|cut

matches 'cat' or 'cut'

c(a|u)t

matches 'cat' or 'cut'

c[a|u]t

matches 'cat','c|t' or 'cut'

[pP]rashant

matches 'prashant' or 'Prashant'

(Prashant|Narayan)Mhatre

matches 'PrashantMhatre' or 'NarayanMhatre'

(a|[bc])d



matches 'ad' or 'bd' or 'cd'


If you understood the above examples, I guess the concept is clear to you. There are different ways to get the desired results.

[abc],[a-c],(a|b|c) are effectively the same but this CANNOT BE GENERALISED. (don't get any shortcut ideas, this is just a coincidence)


Why Character Classes?

(1) Easy to specify ranges [a-z] covers all 26 letters than writing them individually


(2) Easy translations tr/[A-Z]/[a-z]

(3) Compact representation [pnm] Instead of (p|n|m)



[A-Z].*

Any string beginning with UPPERCASE letter

[^a-c].*

Any string not beginning with 'a', 'b', or 'c'

[A-Z]{2}.*

Any string beginning with 2 UPPERCASE letters






Few more examples to firm up the concept in your mind.



























/[0-9]+/

line contains at least 1 digit ANYWHERE

/^[0-9]+/

line contains at least 1 digit in the BEGINNING

/[0-9]+$/

line contains at least 1 digit at the END

/^[0-9]+$/

entire line contains ONLY DIGITS

Whitespace: space (ascii 32), tab (\t), new line (\n), carriage return (\r)

Search and Replace: (Very useful in sed)



s/pnm/Prashant/

will replace the FIRST occurrence of pnm with Prashant

s/pnm/Prashant/g

will replace ALL occurrences of pnm with Prashant

s/^[ \t]*//

Delete spaces and tabs in front of each line (ltrim)

s/[ \t]*$//

Delete spaces and tabs at the end of each line (rtrim)

s/^[ \t]*//;s/[ \t]*$//

Delete leading and trailing spaces (trim)

/^prashant$/

Line contains only 'prashant', nothing else

/^prashant$/i

Same as above, case insensitive match



Delete Blank Lines



Delete lines starting with character 'a'

/^.{5}ant/

If 'ant' is a part of a line from 6th character

Back referencing / tagging: Allows us group and reuse matches

( ) Group text without capturing alternation (Prashant|Mhatre)


\( \) Group text with capturing the result



File: test_file


A|-|Prashant Mhatre|Washington & Tokyo</FONT>


sed 's/^A|.|\(.*\)|.*/\1/' test_file


Prashant Mhatre


sed 's/^.*|\(.*\)|\(.*\)<\/FONT>/\1 \2/' test_file

Prashant Mhatre Washington & Tokyo






































Perl specific

\d

any digit

\w

any character

\s

any whitespace character

\D



= [^\d] Any noncharacter

\W

= [^\w] any nonword character

\S

= [^\s] any nonwhitespace character

[\d\D]

Any digit and any non digit, i.e. match anything (including newline)

[^\d\D]

anything that is not digit, not non-digit, hence nothing

.

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Regular Expressions

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