NCNU Linux User NCNU Linux User Group 2010 Group 2010

<Regular Expression><Regular Expression>王惟綸王惟綸 (Wei-Lun Wang)(Wei-Lun Wang)

2010/07/072010/07/07

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OutlineOutline

What’s a Regular Expression?What’s a Regular Expression? The PurposeThe Purpose What’s grep?What’s grep? Various OperatorsVarious Operators Extended Regular ExpressionsExtended Regular Expressions ExercisesExercises ReferencesReferences

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What’s a Regular What’s a Regular Expression?Expression?

A A regular expressionregular expression is a pattern that d is a pattern that describes a set of strings. escribes a set of strings.

ExamplesExamplesXX[[22--77] ] = {X2, X3, X4, X5, X6, X7} = {X2, X3, X4, X5, X6, X7} TT[[aeae]]steste? ? = {Taste, Tast, Teste, Test}= {Taste, Tast, Teste, Test}

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The PurposeThe Purpose

The regular expression is used to procThe regular expression is used to process strings. It makes users easily do ess strings. It makes users easily do sesearchingarching, , replacementreplacement, and , and deletiondeletion th though the aid of special characters.ough the aid of special characters.

TT[[aeae]]steste? ? = {Taste, Tast, Teste, Test} = {Taste, Tast, Teste, Test} -- These four strings, -- These four strings, TasteTaste, , TastTast, , TesteTeste,, and and TestTest, can be found out by only sea, can be found out by only searching the pattern “Trching the pattern “T[[aeae]]steste??”.”.

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What’s grep?What’s grep? gglobal lobal rregular egular eexpression xpression pprintrint

The The grepgrep command searches for the command searches for the pattern specified by the pattern specified by the PatternPattern parameter and writes each matching line parameter and writes each matching line to standard output. to standard output.

[-i ][-i ] : ignore the type of upper and lower : ignore the type of upper and lower cases cases [-v][-v] : inverse the output : inverse the output

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alias & unaliasalias & unalias

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Various OperatorsVarious Operators

1.1. [ ][ ] presents any one character among those presents any one character among those characters inside.characters inside.

2.2. [ - ][ - ] presents any one character among the code presents any one character among the code range. range.

3.3. [^ ][^ ] represents the characters not in the range of a represents the characters not in the range of a list.list.

4.4. ^ ^ Matches the empty string at the beginning of a Matches the empty string at the beginning of a line.line.

5.5. $ $ Matches the empty string at the end of a line.Matches the empty string at the end of a line.

6.6. . . Matches any single character.Matches any single character.

7.7. * * The preceding item will be matched zero or The preceding item will be matched zero or more times.more times.

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1. [ ]1. [ ] presents any one character among those characters inside. presents any one character among those characters inside.

th[ei] = {the, thi}th[ei] = {the, thi}

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2. [ - ]2. [ - ] presents any one character among the code range. presents any one character among the code range. LANG=C ： 0 1 2 3 4 ... A B C D ... Z a b c d ...z LANG=zh_TW.Big5 ： 0 1 2 3 4 ... a A b B c C d D ... z Z

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LANG=C ： 0 1 2 3 4 ... A B C D ... Z a b c d ...z LANG=zh_TW.Big5 ： 0 1 2 3 4 ... a A b B c C d D ... z Z

2. [ - ]2. [ - ] presents any one character among the code range. presents any one character among the code range.

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Symbol Meaning

[:alnum:] 代表英文大小寫字元及數字，亦即 0-9, A-Z, a-z

[:alpha:] 代表任何英文大小寫字元，亦即 A-Z, a-z

[:blank:] 代表空白鍵與 [Tab] 按鍵兩者[:cntrl:] 代表鍵盤上面的控制按鍵，亦即包括 CR, LF, Tab, Del.. 等等[:digit:] 代表數字而已，亦即 0-9

[:graph:] 除了空白字元 ( 空白鍵與 [Tab] 按鍵 ) 外的其他所有按鍵[:lower:] 代表小寫字元，亦即 a-z

[:print:] 代表任何可以被列印出來的字元[:punct:] 代表標點符號 (punctuation symbol) ，亦即： " ' ? ! ; : # $...

[:upper:] 代表大寫字元，亦即 A-Z

[:space:] 任何會產生空白的字元，包括空白鍵 , [Tab], CR 等等

[:xdigit:]代表 16 進位的數字類型，因此包括： 0-9, A-F, a-f 的數字與字元

2. [ - ]2. [ - ] presents any one character among the code range. presents any one character among the code range.

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3. [^3. [^ ]] represents the characters not in the range of a list. represents the characters not in the range of a list.

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4. ^ 4. ^ Matches the empty string at the beginning of a line.Matches the empty string at the beginning of a line.

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5. $ 5. $ Matches the empty string at the end of a line. Matches the empty string at the end of a line.

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6. . 6. . Matches any single character.Matches any single character.

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7. * 7. * The preceding item will be matched zero or more times.The preceding item will be matched zero or more times.

go* = {g, go, goo, gooo, …}go* = {g, go, goo, gooo, …}

goo* = {go, goo, gooo, …}goo* = {go, goo, gooo, …}

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Extended Regular Extended Regular ExpressionsExpressions

In basic regular expressions the metacharacters "?", "+",In basic regular expressions the metacharacters "?", "+", "{", "|", "(", and ")" lose their special meaning; instead use "{", "|", "(", and ")" lose their special meaning; instead use the the backslashed versionsbackslashed versions "\?", "\+", "\{", "\|", "\(", and "\)". "\?", "\+", "\{", "\|", "\(", and "\)".

Using Using grep -Egrep -E or or egrepegrep instead of grep. instead of grep.

1.1. ++ The preceding item will be matched one or more time The preceding item will be matched one or more times. s.

2.2. ? ? The preceding item will be matched zero or one time. The preceding item will be matched zero or one time. 3.3. | | represents the preceding item or the following item. represents the preceding item or the following item.4.4. ( )( ) represents group strings. represents group strings.5.5. {N}{N} The preceding item is matched exactly N times. The preceding item is matched exactly N times. 6.6. {N, }{N, } The preceding item is matched N or more times. The preceding item is matched N or more times. 7.7. {N,M}{N,M} The preceding item is matched at least N times, The preceding item is matched at least N times,

but not more than M times. but not more than M times.

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1. +1. + The preceding item will be matched one or more times. The preceding item will be matched one or more times.

goo+ = {goo, gooo, goooo, …}goo+ = {goo, gooo, goooo, …}

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2. ?2. ? The preceding item will be matched zero or one time. The preceding item will be matched zero or one time.

goog? = {goog, goo}goog? = {goog, goo}

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3. |3. | represents the preceding item or the following item. represents the preceding item or the following item.

goo|fav = {goo, fav}goo|fav = {goo, fav}

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4. ( )4. ( ) represents group strings. represents group strings.

f(oo|ee)d = {food, feed}f(oo|ee)d = {food, feed}

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5. {N}5. {N} The preceding item is matched exactly N times. The preceding item is matched exactly N times.

go\{2\} = {goo}go\{2\} = {goo}

go\{5\} = {gooooo}go\{5\} = {gooooo}

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6. {N, }6. {N, } The preceding item is matched N or more times. The preceding item is matched N or more times.

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7. {N,M}7. {N,M} The preceding item is matched at least N times, The preceding item is matched at least N times, but not more than M times.but not more than M times.

go\{2,5\}g = {goog, gooog, goooog, gooooog}go\{2,5\}g = {goog, gooog, goooog, gooooog}

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ExercisesExercises

1.1. What does What does grep -n '^[^A-z] 'grep -n '^[^A-z] ' mean? mean?

2.2. How to find out How to find out empty linesempty lines??

3.3. How to find out “How to find out “[LUG2010][LUG2010]”?”?

4.4. Find all files and their contents Find all files and their contents containing the symbol “containing the symbol “**” under ” under /etc/etc

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ReferencesReferences

http://linux.vbird.org/linux_basic/0330reghttp://linux.vbird.org/linux_basic/0330regularex.phpularex.php

http://tldp.org/LDP/Bash-Beginners-Guide/http://tldp.org/LDP/Bash-Beginners-Guide/html/chap_04.htmlhtml/chap_04.html

http://en.wikipedia.org/wiki/Regular_exprhttp://en.wikipedia.org/wiki/Regular_expressionession

http://www.regular-expressions.info/http://www.regular-expressions.info/posix.htmlposix.html