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Regular expression: Difference between revisions
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When processing text files through regular expressions, you can quickly search for or replace strings that match specific rules. Processing is done on a line-by-line basis for string manipulation. Regular expressions are also known as regex, regexp, or pattern matching expressions. | |||
{{LanguageSwitcher | content = [[Regular expression | English]], [[Regular expression in Mandarin|漢字]]}} | |||
{{Raise hand | text = '''Need Help?''' You can use the provided explanatory [[#regular-expression-online-tools|online tools]] to try debugging yourself. }} | |||
== Quick Reference Table == | == Quick Reference Table == | ||
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|} | |} | ||
== Regular Expression Online Tools == | == Regular Expression Online Tools == | ||
Websites for testing regular expression syntax: * | Websites for testing regular expression syntax: | ||
* {{Gd}} [http://regex101.com/ RegEx101] - “Online regex tester and debugger: PHP, PCRE, Python, Golang and JavaScript” - Provides syntax explanations | |||
* {{Gd}} [http://gskinner.com/RegExr/ RegExr] - Learn, Build, & Test RegEx - Provides syntax explanations | |||
* [https://regexper.com/ Regexper] - Visual explanation of syntax using diagrams | |||
* [https://jex.im/regulex/ Regulex：JavaScript Regular Expression Visualizer] - JavaScript Regular Expression Visualizer - Visual explanation using diagrams | |||
* [http://www.rubular.com/ Rubular] - A Ruby regular expression editor and tester | |||
* [http://www.phpliveregex.com/ PHP Live Regex] | |||
* [http://www.regextester.com/ Regex Tester and Debugger Online] - JavaScript, PCRE, PHP | |||
== Common Use Cases == | == Common Use Cases == | ||
=== Replace Newlines with Commas === | === Replace Newlines with Commas === | ||
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Convert to: | Convert to: | ||
==== Method 1: Sublime Text, EmEditor ==== | ==== Method 1: Sublime Text, EmEditor ==== | ||
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# Click “Replace all” | # Click “Replace all” | ||
==== Method 2: Notepad++ ==== | ==== Method 2: Notepad++ ==== | ||
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# Click “Replace All” | # Click “Replace All” | ||
==== Method 3: Microsoft Word ==== | ==== Method 3: Microsoft Word ==== | ||
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# Click “Replace All” | # Click “Replace All” | ||
==== Method 4: Sed command for Linux ==== | ==== Method 4: Sed command for Linux ==== | ||
<syntaxhighlight lang="bash">sed ':a;N;$!ba;s/\n/; /g' old.filename > new.filename</syntaxhighlight> | <syntaxhighlight lang="bash">sed ':a;N;$!ba;s/\n/; /g' old.filename > new.filename</syntaxhighlight> | ||
=== Find IP Addresses (IPv4) === | === Find IP Addresses (IPv4) === | ||
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For Sublime Text v. 3.2.21: - Find: <code>(?:\d{1,3}\.){3}\d{1,3}</code> | For Sublime Text v. 3.2.21: - Find: <code>(?:\d{1,3}\.){3}\d{1,3}</code> | ||
=== Remove Black Squares (UNIX Line Endings LF) === | === Remove Black Squares (UNIX Line Endings LF) === | ||
Using Notepad++: 1. Menu: Find -> Replace 2. Search mode: Check “Extended mode” - Find: <code>\n\n</code> (2 LF characters) - Replace with: <code>\r\n</code> (CR and LF) | Using Notepad++: 1. Menu: Find -> Replace 2. Search mode: Check “Extended mode” - Find: <code>\n\n</code> (2 LF characters) - Replace with: <code>\r\n</code> (CR and LF) | ||
=== Add Quotes Around Elements === | === Add Quotes Around Elements === | ||
==== Add Quotes Around Array Elements ==== | ==== Add Quotes Around Array Elements ==== | ||
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'''Method 3: Notepad++''' (Enable “Regular expression” search mode) - Find: <code>([^\s|,]+)</code> - Replace with: <code>'$1'</code> (for single quotes) or <code>"$1"</code> (for double quotes) | '''Method 3: Notepad++''' (Enable “Regular expression” search mode) - Find: <code>([^\s|,]+)</code> - Replace with: <code>'$1'</code> (for single quotes) or <code>"$1"</code> (for double quotes) | ||
=== Find Non-ASCII Characters (Chinese/Non-English Text) === | === Find Non-ASCII Characters (Chinese/Non-English Text) === | ||
==== In LibreOffice ==== | ==== In LibreOffice ==== | ||
<pre>[^\u0000-\u0080]+</pre> | <pre>[^\u0000-\u0080]+</pre> | ||
==== Find Chinese Characters in Google Sheets ==== | ==== Find Chinese Characters in Google Sheets ==== | ||
Example: If A2 contains any Chinese character, display “Chinese”, otherwise display “English”: | Example: If cell {{kbd | key=A2}} contains any Chinese character, display “Chinese”, otherwise display “English”: | ||
<pre>=IF(REGEXMATCH(A2, "[\一-\龥]"), "Chinese", "English")</pre> | <pre>=IF(REGEXMATCH(A2, "[\一-\龥]"), "Chinese", "English")</pre> | ||
< | |||
==== Find Non-ASCII Characters in Google Sheets ==== | |||
Extract non-ASCII characters (such as Chinese, Japanese, emoji, etc.) from cell {{kbd | key=A2}} | |||
<pre> | |||
=IF(ISERROR(REGEXEXTRACT(A2, "[^\x00-\x80]+")), "", REGEXEXTRACT(A2, "[^\x00-\x80]+")) | |||
</pre> | |||
Explanation of regular expression {{kbd | key=<nowiki>[^\x00-\x80]+</nowiki>}} | |||
* {{kbd | key=<nowiki>[\x00-\x80]</nowiki>}}: Represents the ASCII character range (character codes 0-128). (1) Standard ASCII range: 0-127 ({{kbd | key=<nowiki>0x00-0x7F</nowiki>}} aka * {{kbd | key=<nowiki>[\x00-\x7F]</nowiki>}})<ref>[https://www.commfront.com/pages/ascii-chart ASCII Chart – CommFront]</ref> (2) Character 128 (({{kbd | key=<nowiki>0x80</nowiki>}}) is actually the first character in the extended ASCII range, not part of the original ASCII standard.<ref>[https://en.wikipedia.org/wiki/UTF-8 UTF-8 - Wikipedia]</ref><ref>[https://en.wikipedia.org/wiki/Control_character Control character - Wikipedia]</ref> | |||
* {{kbd | key=<nowiki>[^...]</nowiki>}}: Means "not" these characters | |||
* {{kbd | key=<nowiki>+</nowiki>}}: Means one or more | |||
Overall meaning: Matches one or more non-ASCII characters | |||
==== Find Chinese Characters in MySQL ==== | ==== Find Chinese Characters in MySQL ==== | ||
Find rows where <code>column_name</code> contains Chinese characters: | Find rows where <code>column_name</code> contains Chinese characters: | ||
< | <pre lang="sql">SELECT `column_name` | ||
FROM `table_name` | |||
WHERE HEX(`column_name`) REGEXP '^(..)*(E[4-9])';</pre> | |||
Query condition used to match records where the <code>column_name</code> field contains only Chinese characters. | |||
<pre lang="sql">SELECT `column_name` | |||
FROM `table_name` | FROM `table_name` | ||
WHERE | WHERE `column_name` REGEXP '^[一-龯]+$';</pre> | ||
< | |||
Explanation: | |||
* {{kbd | key=<nowiki>[一-龯]</nowiki>}} - Character set that matches all characters from "一" to "龯" in Unicode | |||
* "一" has Unicode code point {{kbd | key=<nowiki>U+4E00</nowiki>}}<ref>[https://www.compart.com/en/unicode/U+4E00 “一” U+4E00 CJK Unified Ideograph-4E00 Unicode Character]</ref> | |||
* "龯" has Unicode code point {{kbd | key=<nowiki>U+9FEF</nowiki>}}<ref>[https://www.compart.com/en/unicode/U+9FAF “龯” U+9FAF CJK Unified Ideograph-9FAF Unicode Character]</ref> | |||
* This range U+4E00-U+9FFF already covers over 99% of daily Chinese usage requirements [https://en.wikipedia.org/wiki/CJK_Unified_Ideographs_Extension_B Extension B] and later blocks mainly contain ancient Chinese characters, variant characters, etc., which rarely appear in modern texts | |||
==== Find Non-ASCII Characters in MySQL ==== | ==== Find Non-ASCII Characters in MySQL ==== | ||
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FROM `table_name` | FROM `table_name` | ||
WHERE `column_name` <> CONVERT(`column_name` USING ASCII)</syntaxhighlight> | WHERE `column_name` <> CONVERT(`column_name` USING ASCII)</syntaxhighlight> | ||
==== Find Chinese Characters in PHP ==== | ==== Find Chinese Characters in PHP ==== | ||
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preg_match_all($pattern, $string, $matches, PREG_OFFSET_CAPTURE); | preg_match_all($pattern, $string, $matches, PREG_OFFSET_CAPTURE); | ||
var_dump($matches);</syntaxhighlight> | var_dump($matches);</syntaxhighlight> | ||
=== Find ASCII Characters in PHP === | === Find ASCII Characters in PHP === | ||
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echo "Contains non-ASCII characters"; | echo "Contains non-ASCII characters"; | ||
}</syntaxhighlight> | }</syntaxhighlight> | ||
=== Remove Empty Lines === | === Remove Empty Lines === | ||
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'''Using Notepad++ v7.8.7:''' - Menu: Edit -> Line Operations -> Remove Empty Lines (Including Blank Lines) | '''Using Notepad++ v7.8.7:''' - Menu: Edit -> Line Operations -> Remove Empty Lines (Including Blank Lines) | ||
=== Find Non-Whitespace Text === | === Find Non-Whitespace Text === | ||
* Find: <code>[^\s]+</code> | * Find: <code>[^\s]+</code> | ||
=== Convert Symbol-Separated Text to Line-by-Line Display === | === Convert Symbol-Separated Text to Line-by-Line Display === | ||
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'''Using Sublime Text or EmEditor:''' - Find: <code>([^、]+)([、]{1})</code> - Replace with: <code>\1\n</code> | '''Using Sublime Text or EmEditor:''' - Find: <code>([^、]+)([、]{1})</code> - Replace with: <code>\1\n</code> | ||
=== Replace Multiple Spaces with Tab Characters === | === Replace Multiple Spaces with Tab Characters === | ||
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'''Using Sublime Text:''' - Find: <code>([^\S\n]+)</code> or <code>([^\S\r\n]+)</code> or <code>\s\s+</code> - Replace with: <code>\t</code> | '''Using Sublime Text:''' - Find: <code>([^\S\n]+)</code> or <code>([^\S\r\n]+)</code> or <code>\s\s+</code> - Replace with: <code>\t</code> | ||
=== Remove Leading/Trailing Whitespace === | === Remove Leading/Trailing Whitespace === | ||
==== Remove Leading Whitespace ==== | ==== Remove Leading Whitespace ==== | ||
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* Replace with: (empty) | * Replace with: (empty) | ||
==== Remove Trailing Whitespace ==== | ==== Remove Trailing Whitespace ==== | ||
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* Replace with: (empty) | * Replace with: (empty) | ||
==== Remove Both Leading and Trailing Whitespace ==== | ==== Remove Both Leading and Trailing Whitespace ==== | ||
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* Replace with: (empty) | * Replace with: (empty) | ||
== Text Editors Supporting Regular Expressions == | == Text Editors Supporting Regular Expressions == | ||
Various text editors support regular expressions including: - Sublime Text - EmEditor - Notepad++ - Visual Studio Code - Atom - Vim/Neovim | Various text editors support regular expressions including: - Sublime Text - EmEditor - Notepad++ - Visual Studio Code - Atom - Vim/Neovim | ||
== Syntax Reference == | == Syntax Reference == | ||
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* Non-whitespace: <code>\S</code> - Does not include half-width spaces and full-width spaces | * Non-whitespace: <code>\S</code> - Does not include half-width spaces and full-width spaces | ||
== Troubleshooting Regular Expressions == | == Troubleshooting Regular Expressions == | ||
'''Tips:''' 1. Use online tools like regex101 to understand your syntax 2. Test with small data: Prepare small file data to verify syntax 3. Highlight or output matched text for debugging 4. Simplify the syntax when encountering issues 5. Try alternative syntax due to compatibility issues (e.g., <code>\d</code> to <code>[0-9]+</code>) | '''Tips:''' 1. Use online tools like regex101 to understand your syntax 2. Test with small data: Prepare small file data to verify syntax 3. Highlight or output matched text for debugging 4. Simplify the syntax when encountering issues 5. Try alternative syntax due to compatibility issues (e.g., <code>\d</code> to <code>[0-9]+</code>) | ||
== Alternative Solutions == | == Alternative Solutions == | ||
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* Copy multiple rows and paste between different applications (compatibility varies) | * Copy multiple rows and paste between different applications (compatibility varies) | ||
== Further Reading == | == Further Reading == | ||
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* Platform-specific regular expression documentation | * Platform-specific regular expression documentation | ||
{{Template:Data factory flow}} | {{Template: Data factory flow}} | ||
[[Category:Regular expression]] [[Category:Software]] [[Category:Programming]] [[Category:Data Science]] [[Category:Search]] [[Category:String manipulation]] | [[Category: Regular expression]] | ||
[[Category: Software]] | |||
[[Category: Programming]] | |||
[[Category: Data Science]] | |||
[[Category: Search]] | |||
[[Category: String manipulation]] | |||
[[Category: Revised with LLMs] | |||