Regular Expressions 101

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An explanation of your regex will be automatically generated as you type.
Detailed match information will be displayed here automatically.
  • All Tokens
  • Common Tokens
  • General Tokens
  • Anchors
  • Meta Sequences
  • Quantifiers
  • Group Constructs
  • Character Classes
  • Flags/Modifiers
  • Substitution
  • A single character of: a, b or c
    [abc]
  • A character except: a, b or c
    [^abc]
  • A character in the range: a-z
    [a-z]
  • A character not in the range: a-z
    [^a-z]
  • A character in the range: a-z or A-Z
    [a-zA-Z]
  • Any single character
    .
  • Alternate - match either a or b
    a|b
  • Any whitespace character
    \s
  • Any non-whitespace character
    \S
  • Any digit
    \d
  • Any non-digit
    \D
  • Any word character
    \w
  • Any non-word character
    \W
  • Non-capturing group
    (?:...)
  • Capturing group
    (...)
  • Zero or one of a
    a?
  • Zero or more of a
    a*
  • One or more of a
    a+
  • Exactly 3 of a
    a{3}
  • 3 or more of a
    a{3,}
  • Between 3 and 6 of a
    a{3,6}
  • Start of string
    ^
  • End of string
    $
  • A word boundary
    \b
  • Non-word boundary
    \B

Regular Expression
No Match

/
/
g

Test String

Code Generator

Generated Code

# coding=utf8 # the above tag defines encoding for this document and is for Python 2.x compatibility import re regex = r"(?<=^|[\n;](?:[\t ]*(?:\w+ )?)?)import\s*(?<type>type(?=\s+))?(?:[\s\"']*(?<imports>[\w\t\n\r \"$'*,/{}-]+?)\s+from\s*)?[\"']\s*(?<specifier>(?:(?<='\s*)[^']*[^\s'](?=\s*'))|(?:(?<=\"\s*)[^\"]*[^\s\"](?=\s*\")))\s*[\"'](?:\s+assert\s+(?<assertion>{[\w\t\n\r \"':]+?}))?(?=[\s;]*)" test_str = ("/**\n" " * @file Interfaces\n" " * @module mlly/interfaces\n" " */\n\n" "export type { default as DynamicImport } from './import-dynamic'\n" "export type { default as StaticImport } from './import-static'\n" "export type { default as ResolveOptions } from './options-resolve'\n" "export type { default as ResolveAliasOptions } from './options-resolve-alias'\n" "export type { default as Statement } from './statement'\n" "export type { default as ExportStatement } from './statement-export'\n" "export type { default as ImportStatement } from './statement-import'\n" "export type { default as RequireStatement } from './statement-require'\n\n" "import { CONDITIONS, RESOLVE_EXTENSIONS } from '#src/constants'\n" "import type { ResolveOptions } from '#src/interfaces'\n" "import type { SpecifierType } from '#src/types'\n" "import isBuiltin from '@flex-development/is-builtin'\n" "import { moduleResolve, type ErrnoException } from 'import-meta-resolve'\n" "import { pathToFileURL, URL } from 'node:url'\n" "import upath from 'upath'\n" "import toBareSpecifier from './to-bare-specifier'\n" "import toRelativeSpecifier from './to-relative-specifier'\n" "import 'file:///home/dir/file.ts'\n\n" "import pkg from './package.json' assert { type:'json' }\n" "import * as color from 'colorette'\n" "import consola from 'consola'\n" "import { defu } from 'defu'\n" "import type { Format } from 'esbuild'\n" "import fse from 'fs-extra'\n" "import * as pathe from 'pathe'\n" "import { resolve } from 'node:path'\n" "import url from 'node:url'\n" "import type { PackageJson } from 'pkg-types'\n" "import pb from 'pretty-bytes'\n" "import { EXT_DTS_REGEX, IGNORE_PATTERNS } from './config/constants'\n" "import loadBuildConfig from './config/load'\n" "import type { Config, Entry, Result } from './interfaces'\n" "import type { OutputExtension } from './types'\n" "import { readPackage, type PackageJson } from \"read-pkg\"\n" "import {OutputExtension} from './types'\n" "import analyzeResults from './utils/analyze-results'\n" "import esbuilder from './utils/esbuilder'; import write from './utils/write';import write2 from './utils/write'\n" "// import write from './utils/write'\n" "import 'side-effect.mjs'\n" "import type StatementType from '../types/statement-type'\n" "import type {\n" " BuildOptions,\n" " BuildResult,\n" " OutputFile,\n" " Plugin,\n" " PluginBuild\n" "} from './esbuild'\n\n" "import defaultExport from \"module-name\";\n" "import * as name from \"module-name\";\n" "import { export1 } from \"module-name\";\n" "import { export1 as alias1 } from \"module-name\";\n" "import { default as alias } from \"module-name\";\n" "import { export1, export2 } from \"module-name\";\n" "import { export1, export2 as alias2 } from \"module-name\";\n" "import { 'string name' as alias } from \"module-name\";\n" "import { \"string name\" as alias } from \"module-name\";\n" "import defaultExport, { export1 } from \"module-name\";\n" "import defaultExport, * as name from \"module-name\";\n" "import \"module-name\";\n" "import 'module-name';\n" "import './polyfill.mjs'\n" "import { \"h-i\" as hi } from './hi.js'\n" "import { 'j-k' as jk } from \"./jk.js\"\n\n" "declare module '__fixtures__/values' {\n" " import MAX_VALUE from '#fixtures/max-value'\n" " import MIN_VALUE from '#fixtures/min-value'\n" "}\n\n" "const ERR_UNSUPPORTED_DIR_IMPORT: NodeErrorConstructor<\n" " ErrorConstructor,\n" " [string, string]\n" "> = createNodeError(\n" " ErrorCode.ERR_UNSUPPORTED_DIR_IMPORT,\n" " Error,\n" " 'Directory import '%s' is not supported resolving ES modules imported from %s'\n" ")\n\n" "const text: string = await resolveModules(output.text, {\n" " conditions: [format === 'esm' ? 'import' : 'require'],\n" " ext: ext as Ext,\n" " extensions,\n" " parent\n" "})\n\n" "/**\n" " * @example\n" " * import write from './utils/write'\n" " * write()\n" " */\n\n" "import { 'j-k' as jk } from \"./jk.js\"") matches = re.finditer(regex, test_str) for matchNum, match in enumerate(matches, start=1): print ("Match {matchNum} was found at {start}-{end}: {match}".format(matchNum = matchNum, start = match.start(), end = match.end(), match = match.group())) for groupNum in range(0, len(match.groups())): groupNum = groupNum + 1 print ("Group {groupNum} found at {start}-{end}: {group}".format(groupNum = groupNum, start = match.start(groupNum), end = match.end(groupNum), group = match.group(groupNum))) # Note: for Python 2.7 compatibility, use ur"" to prefix the regex and u"" to prefix the test string and substitution.

Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Python, please visit: https://docs.python.org/3/library/re.html