了解正则表达式标准，各个之间存在一些差异
- BRE (Basic Regular Expressions)
- ERE (Extended Regular Expressions)
- PCRE (Perl Compatible Regular Expressions)
常用工具
| What | Syntax | Comments/gotchas |
|---|---|---|
| Programming languages | ||
| Perl | PCRE | PCRE is actually a separate implementation from Perl's, with slight differences |
Python's re standard lib | Python's own syntax (Perl-inspired) | |
| Ruby | Ruby's own syntax (Perl-inspired) | |
| Java's java.util.regex | Almost PCRE | |
| Boost.Regex | PCRE | |
| Text editors | ||
| Eclipse | PCRE | |
| Emacs | ? | |
| Netbeans | PCRE | |
| Notepad++ | PCRE (Boost.Regex) | |
| PyCharm | PCRE | Perl-inspired |
| Sublime Text | ? | |
| UltraEdit | PCRE | |
| ViM | ViM | |
| Command-line tools | ||
| awk | ERE | might depend on the implementation |
| grep | BRE, egrep for ERE, grep -P for PCRE (optional) | |
| less | ERE | usually; man page says "regular expression library supplied by your system" |
| screen | plain text | |
| sed | BRE, -E switches to ERE | |
语法差异
| What | Perl/PCRE | Python's re | POSIX (BRE) | POSIX extended (ERE) | ViM |
|---|---|---|---|---|---|
| Basics | |||||
| Custom character class | [...] | [...] | [...] | [...] | [...] |
| Negated custom character class | [^...] | [^...] | [^...] | [^...] | [^...] |
| \ special in class? | yes | yes | no, ] escaped if comes first | no, ] escaped if comes first | yes |
| Ranges | [a-z], - escaped if comes last | [a-z], - escaped if first or last | [a-z], - escaped if comes last | [a-z], - escaped if comes last | |
| Alternation | | | | | \| | | | \| \& (low precedence) |
| Escaped character | \033 \x1B \x{1234} \N{name} \N{U+263D} | \x12 | \%d123 \%x2A \%u1234 \%U1234ABCD | ||
| Character classes | |||||
| Any character (except newline) | . | . | . | . | . |
| Any character (including newline) | \_. | ||||
Match a "word" character (alphanumeric plus _) | \w [[:word:]] | \w | \w | \w | \w |
| Case | [[:upper:]] / [[:lower:]] | [[:upper:]] / [[:lower:]] | [[:upper:]] / [[:lower:]] | \u [[:upper:]] / \l [[:lower:]] | |
| Match a non-"word" character | \W | \W | \W | ||
| Match a whitespace character (except newline) | \s [[:space:]] | \s [[:space:]] | \s [[:space:]] | ||
| Whitespace including newline | \s [[:space:]] | \s | \_s | ||
| Match a non-whitespace character | \S | \S | [^[:space:]] | [^[:space:]] | \S [^[:space:]] |
| Match a digit character | \d [[:digit:]] | \d | [[:digit:]] | [[:digit:]] | \d [[:digit:]] |
| Match a non-digit character | \D | \D | [^[:digit:]] | [^[:digit:]] | \D [^[:digit:]] |
| Any hexadecimal digit | [[:xdigit:]] | [[:xdigit:]] | [[:xdigit:]] | \x [[:xdigit:]] | |
| Any octal digit | \o | ||||
| Any graphical character excluding "word" characters | [[:punct:]] | [[:punct:]] | [[:punct:]] | [[:punct:]] | |
| Any alphabetical character | [[:alpha:]] | [[:alpha:]] | [[:alpha:]] | \a [[:alpha:]] | |
| Non-alphabetical character | [^[:alpha:]] | [^[:alpha:]] | \A [^[:alpha:]] | ||
| Any alphanumerical character | [[:alnum:]] | [[:alnum:]] | [[:alnum:]] | [[:alnum:]] | |
| ASCII | [[:ascii:]] | ||||
| Character equivalents (e = é = è) (as per locale) | [[=e=]] | [[=e=]] | [[=e=]] | ||
| Zero-width assertions | |||||
| Word boundary | \b | \b | \b | \b | \< / \> |
| Anywhere but word boundary | \B | \B | \B | \B | |
| Beginning of line/string | ^ / \A | ^ / \A | ^ | ^ | ^ (beginning of pattern ) \_^ |
| End of line/string | $ / \Z | $ / \Z | $ | $ | $ (end of pattern) \_$ |
| Captures and groups | |||||
| Capturing group | (...) (?<name>...) | (...) (?P<name>...) | \(...\) | (...) | \(...\) |
| Non-capturing group | (?:...) | (?:...) | \%(...\) | ||
| Backreference to a specific group. | \1 \g1 \g{-1} | \1 | \1 | \1 non-official | \1 |
| Named backreference | \g{name} \k<name> | (?P=name) | |||
| Look-around | |||||
| Positive look-ahead | (?=...) | (?=...) | \(...\)\@= | ||
| Negative look-ahead | (?!...) | (?!...) | \(...\)\@! | ||
| Positive look-behind | (?<=...) | (?<=...) | \(...\)\@<= | ||
| Negative look-behind | (?<!...) | (?<!...) | \(...\)\@<! | ||
| Multiplicity | |||||
| 0 or 1 | ? | ? | \? | ? | \? |
| 0 or more | * | * | * | * | * |
| 1 or more | + | + | \+ | + | \+ |
| Specific number | {n} {n,m} {n,} | {n} {n,m} {n,} | \{n\} \{n,m\} \{n,\} | {n} {n,m} {n,} | \{n} \{n,m} \{n,} |
| 0 or 1, non-greedy | ?? | ?? | |||
| 0 or more, non-greedy | *? | *? | \{-} | ||
| 1 or more, non-greedy | +? | +? | |||
| Specific number, non-greedy | {n,m}? {n,}? | {n,m}? {n,}? | \{-n,m} \{-n,} | ||
| 0 or 1, don't give back on backtrack | ?+ | ||||
| 0 or more, don't give back on backtrack | *+ | ||||
| 1 or more, don't give back on backtrack | ++ | ||||
| Specific number, don't give back on backtrack | {n,m}+ {n,}+ | ||||
| Other | |||||
| Independent non-backtracking pattern | (?>...) | \(...\)\@> | |||
| Make case-sensitive/insensitive | (?i) / (?-i) | (?i) / (?-i) | \c / \C | ||
BRE ERE 需要注意 () {} 的区别，另外都不支持 \d\D