I'm using Rails 5 and Ruby 2.4. I'm confused about how to match a regular expression in which the word following is not equal to a certain thing. I want to match a number, a "/" and another number provided that the word after is not equal to "aaa". So this would match
1/3 ddd
as would
7/10 eee
and also
33/2
but not
4/555aaa
or
4/5 aaa
I have figured out how to craft my regex this far ...
2.4.0 :006 > re = /\d+[[:space:]]*\/[[:space:]]*\d+/
=> /\d+[[:space:]]*\/[[:space:]]*\d+/
...
2.4.0 :009 > string = "1/2 aaa"
=> "1/2 aaa"
2.4.0 :010 > string.match(re)
=> #<MatchData "1/2">
but I don't know how to add the clause about "the last word shall not be 'aaa'". How do I do that?
I sugges using a negative lookahead (?![[:space:]]*aaa) combined with a possessive ++ quantifier after last \d:
/\d+[[:space:]]*\/[[:space:]]*\d++(?![[:space:]]*aaa)/
^^^^^^^^^^^^^^^^^^^^^
See the Rubular demo
Details
\d+ - 1 or more digits
[[:space:]]* - zero or more whitespaces
\/ - a forward slash
[[:space:]]* - zero or more whitespaces
\d++ - 1 or more digits, matched possessively, so that the negative lookahead that follows could not make the engine backtrack into this subpattern (and yield a smaller portion of digits that are not followed with the lookahead pattern)
(?![[:space:]]*aaa) - the negative lookahead that fails the match if there is no 0+ whitespaces and aaa immediately to the right of the current location.
Elixir provides Path.wildcard, which uses the Erlang :filelib.wildcard function internally.
Matching is case-sensitive, for example, "a" does not match "A".
(http://erlang.org/doc/man/filelib.html#wildcard-1)
Please is there a case-insensitive alternative?
There's no built in option to do this, but since the wildcard syntax supports character alternations similar to regex, you can replace every letter with an alternation of its lower and upper case versions, e.g. f0o -> [fF]0[oO], and then pass that to Path.wildcard/1. Here's a simple implementation that does this for ASCII letters:
defmodule A do
def case_insensitive_glob(glob) do
Regex.replace(~r/[a-zA-Z]/, glob, fn letter ->
"[#{String.downcase(letter)}#{String.upcase(letter)}]"
end)
end
end
glob = A.case_insensitive_glob("**/*reAdmE.*") |> IO.inspect
Path.wildcard(glob) |> IO.inspect
Running this in the OTP source code produces all files with their name containing "reAdmE." in any case.
"**/*[rR][eE][aA][dD][mM][eE].*"
["README.md", "erts/emulator/pcre/README.pcre_update.md",
"lib/erl_interface/src/README.internal",
"lib/ic/examples/pre_post_condition/ReadMe.txt", "xcomp/README.md"]
I've verified the output's correctness with find:
$ find . -iname 'readme.*'
./erts/emulator/pcre/README.pcre_update.md
./lib/erl_interface/src/README.internal
./lib/ic/examples/pre_post_condition/ReadMe.txt
./README.md
./xcomp/README.md
I have a phoenix/elixir app and need to only have ASCII characters in my String.
From what I tried and found here, this can only be done properly by Iconv.
:iconv.convert "utf-8", "ascii//translit", "árboles más grandes"
# arboles mas grandes
but when I run it on my mac it says:
# 'arboles m'as grandes
It seems it returns multiple letters for any character that had more than one byte in size and the order is turned around.
for example:
ä will turn to \"a
á will turn to 'a
ß will turn to ss
ñ will turn to ~n
I'm running it with IEx 1.2.5 on Mac.
Is there any way around this, or generally a better way to achieve the same functionality as rails transliterate?
EDIT:
So here is the update rails-like behaviour according to the accepted answer on Henkik N. It does the same thing as rails parameterize( turn whatever string into sth. that you can use as a part of a url)
defmodule RailsLikeHelpers do
require Inflex
# replace accented chars with their ascii equivalents
def transliterate_string(abc) do
return :iconv.convert("utf-8", "ascii//translit", String.normalize(abc))
end
def parameterize_string(abc) do
parameterize_string(abc, "_")
end
def parameterize_string(abc,seperator) do
abc
|> String.strip
|> transliterate_string
|> Inflex.parameterize(seperator) # turns "Your Momma" into "your_momma"
|> String.replace(~r[#{Regex.escape(seperator)}{2,}],seperator) # No more than one of the separator in a row.
end
end
Running it through Unicode decomposition (as people kind of mentioned in the forum thread you linked to) seems to do it on my OS X:
iex> :iconv.convert "utf-8", "ascii//translit", String.normalize("árboles más grandes", :nfd)
"arboles mas grandes"
Decomposition means it will be normalized so that e.g. "á" is represented as two Unicode codepoints ("a" and a combining accent) as opposed to a composed form where it's a single Unicode codepoint. So I guess iconv's ASCII transliteration removes standalone accents/diacritics, but converts composed characters to things like 'a.
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What is this?
This is a collection of common Q&A. This is also a Community Wiki, so everyone is invited to participate in maintaining it.
Why is this?
regex is suffering from give me ze code type of questions and poor answers with no explanation. This reference is meant to provide links to quality Q&A.
What's the scope?
This reference is meant for the following languages: php, perl, javascript, python, ruby, java, .net.
This might be too broad, but these languages share the same syntax. For specific features there's the tag of the language behind it, example:
What are regular expression Balancing Groups? .net
The Stack Overflow Regular Expressions FAQ
See also a lot of general hints and useful links at the regex tag details page.
Online tutorials
RegexOne ↪
Regular Expressions Info ↪
Quantifiers
Zero-or-more: *:greedy, *?:reluctant, *+:possessive
One-or-more: +:greedy, +?:reluctant, ++:possessive
?:optional (zero-or-one)
Min/max ranges (all inclusive): {n,m}:between n & m, {n,}:n-or-more, {n}:exactly n
Differences between greedy, reluctant (a.k.a. "lazy", "ungreedy") and possessive quantifier:
Greedy vs. Reluctant vs. Possessive Quantifiers
In-depth discussion on the differences between greedy versus non-greedy
What's the difference between {n} and {n}?
Can someone explain Possessive Quantifiers to me? php, perl, java, ruby
Emulating possessive quantifiers .net
Non-Stack Overflow references: From Oracle, regular-expressions.info
Character Classes
What is the difference between square brackets and parentheses?
[...]: any one character, [^...]: negated/any character but
[^] matches any one character including newlines javascript
[\w-[\d]] / [a-z-[qz]]: set subtraction .net, xml-schema, xpath, JGSoft
[\w&&[^\d]]: set intersection java, ruby 1.9+
[[:alpha:]]:POSIX character classes
[[:<:]] and [[:>:]] Word boundaries
Why do [^\\D2], [^[^0-9]2], [^2[^0-9]] get different results in Java? java
Shorthand:
Digit: \d:digit, \D:non-digit
Word character (Letter, digit, underscore): \w:word character, \W:non-word character
Whitespace: \s:whitespace, \S:non-whitespace
Unicode categories (\p{L}, \P{L}, etc.)
Escape Sequences
Horizontal whitespace: \h:space-or-tab, \t:tab
Newlines:
\r, \n:carriage return and line feed
\R:generic newline php java-8
Negated whitespace sequences: \H:Non horizontal whitespace character, \V:Non vertical whitespace character, \N:Non line feed character pcre php5 java-8
Other: \v:vertical tab, \e:the escape character
Anchors
anchor
matches
flavors
^
Start of string
Common*
^
Start of line
Commonm
$
End of line
Commonm
$
End of text
Common* except javascript
$
Very end of string
javascript*, phpD
\A
Start of string
Common except javascript
\Z
End of text
Common except javascript python
\Z
Very end of string
python
\z
Very end of string
Common except javascript python
\b
Word boundary
Common
\B
Not a word boundary
Common
\G
End of previous match
Common except javascript, python
Term
Definition
Start of string
At the very start of the string.
Start of line
At the very start of the string, andafter a non-terminal line terminator.
Very end of string
At the very end of the string.
End of text
At the very end of the string, andat a terminal line terminator.
End of line
At the very end of the string, andat a line terminator.
Word boundary
At a word character not preceded by a word character, andat a non-word character not preceded by a non-word character.
End of previous match
At a previously set position, usually where a previous match ended.At the very start of the string if no position was set.
"Common" refers to the following: icu java javascript .net objective-c pcre perl php python swift ruby
* Default |
m Multi-line mode. |
D Dollar end only mode.
Groups
(...):capture group, (?:):non-capture group
Why is my repeating capturing group only capturing the last match?
\1:backreference and capture-group reference, $1:capture group reference
What's the meaning of a number after a backslash in a regular expression?
\g<1>123:How to follow a numbered capture group, such as \1, with a number?: python
What does a subpattern (?i:regex) mean?
What does the 'P' in (?P<group_name>regexp) mean?
(?>):atomic group or independent group, (?|):branch reset
Equivalent of branch reset in .NET/C# .net
Named capture groups:
General named capturing group reference at regular-expressions.info
java: (?<groupname>regex): Overview and naming rules (Non-Stack Overflow links)
Other languages: (?P<groupname>regex) python, (?<groupname>regex) .net, (?<groupname>regex) perl, (?P<groupname>regex) and (?<groupname>regex) php
Lookarounds
Lookaheads: (?=...):positive, (?!...):negative
Lookbehinds: (?<=...):positive, (?<!...):negative
Lookbehind limits in:
Lookbehinds need to be constant-length php, perl, python, ruby
Lookarounds of limited length {0,n} java
Variable length lookbehinds are allowed .net
Lookbehind alternatives:
Using \K php, perl (Flavors that support \K)
Alternative regex module for Python python
The hacky way
JavaScript negative lookbehind equivalents External link
Modifiers
flag
modifier
flavors
a
ASCII
python
c
current position
perl
e
expression
php perl
g
global
most
i
case-insensitive
most
m
multiline
php perl python javascript .net java
m
(non)multiline
ruby
o
once
perl ruby
r
non-destructive
perl
S
study
php
s
single line
ruby
U
ungreedy
php r
u
unicode
most
x
whitespace-extended
most
y
sticky ↪
javascript
How to convert preg_replace e to preg_replace_callback?
What are inline modifiers?
What is '?-mix' in a Ruby Regular Expression
Other:
|:alternation (OR) operator, .:any character, [.]:literal dot character
What special characters must be escaped?
Control verbs (php and perl): (*PRUNE), (*SKIP), (*FAIL) and (*F)
php only: (*BSR_ANYCRLF)
Recursion (php and perl): (?R), (?0) and (?1), (?-1), (?&groupname)
Common Tasks
Get a string between two curly braces: {...}
Match (or replace) a pattern except in situations s1, s2, s3...
How do I find all YouTube video ids in a string using a regex?
Validation:
Internet: email addresses, URLs (host/port: regex and non-regex alternatives), passwords
Numeric: a number, min-max ranges (such as 1-31), phone numbers, date
Parsing HTML with regex: See "General Information > When not to use Regex"
Advanced Regex-Fu
Strings and numbers:
Regular expression to match a line that doesn't contain a word
How does this PCRE pattern detect palindromes?
Match strings whose length is a fourth power
How does this regex find triangular numbers?
How to determine if a number is a prime with regex?
How to match the middle character in a string with regex?
Other:
How can we match a^n b^n?
Match nested brackets
Using a recursive pattern php, perl
Using balancing groups .net
“Vertical” regex matching in an ASCII “image”
List of highly up-voted regex questions on Code Golf
How to make two quantifiers repeat the same number of times?
An impossible-to-match regular expression: (?!a)a
Match/delete/replace this except in contexts A, B and C
Match nested brackets with regex without using recursion or balancing groups?
Flavor-Specific Information
(Except for those marked with *, this section contains non-Stack Overflow links.)
Java
Official documentation: Pattern Javadoc ↪, Oracle's regular expressions tutorial ↪
The differences between functions in java.util.regex.Matcher:
matches()): The match must be anchored to both input-start and -end
find()): A match may be anywhere in the input string (substrings)
lookingAt(): The match must be anchored to input-start only
(For anchors in general, see the section "Anchors")
The only java.lang.String functions that accept regular expressions: matches(s), replaceAll(s,s), replaceFirst(s,s), split(s), split(s,i)
*An (opinionated and) detailed discussion of the disadvantages of and missing features in java.util.regex
.NET
How to read a .NET regex with look-ahead, look-behind, capturing groups and back-references mixed together?
Official documentation:
Boost regex engine: General syntax, Perl syntax (used by TextPad, Sublime Text, UltraEdit, ...???)
JavaScript general info and RegExp object
.NET MySQL Oracle Perl5 version 18.2
PHP: pattern syntax, preg_match
Python: Regular expression operations, search vs match, how-to
Rust: crate regex, struct regex::Regex
Splunk: regex terminology and syntax and regex command
Tcl: regex syntax, manpage, regexp command
Visual Studio Find and Replace
General information
(Links marked with * are non-Stack Overflow links.)
Other general documentation resources: Learning Regular Expressions, *Regular-expressions.info, *Wikipedia entry, *RexEgg, Open-Directory Project
DFA versus NFA
Generating Strings matching regex
Books: Jeffrey Friedl's Mastering Regular Expressions
When to not use regular expressions:
Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems. (blog post written by Stack Overflow's founder)*
Do not use regex to parse HTML:
Don't. Please, just don't
Well, maybe...if you're really determined (other answers in this question are also good)
Examples of regex that can cause regex engine to fail
Why does this regular expression kill the Java regex engine?
Tools: Testers and Explainers
(This section contains non-Stack Overflow links.)
Online (* includes replacement tester, + includes split tester):
Debuggex (Also has a repository of useful regexes) javascript, python, pcre
*Regular Expressions 101 php, pcre, python, javascript, java
Regex Pal, regular-expressions.info javascript
Rubular ruby RegExr Regex Hero dotnet
*+ regexstorm.net .net
*RegexPlanet: Java java, Go go, Haskell haskell, JavaScript javascript, .NET dotnet, Perl perl php PCRE php, Python python, Ruby ruby, XRegExp xregexp
freeformatter.com xregexp
*+regex.larsolavtorvik.com php PCRE and POSIX, javascript
Offline:
Microsoft Windows: RegexBuddy (analysis), RegexMagic (creation), Expresso (analysis, creation, free)
MySQL 8.0: Various syntax changes were made. Note especially the doubling of backslashes in some contexts. (This Answer need further editing to reflect the differences.)
I managed to build the parse tree for given sentence and here it is, for the sentence: "The man went home."
T = s(np(det(the), n(man)), vp(v(went), np(n(home))))
1) How to use phrase/2 on this?
How to translate a sentence in a logical language using prolog? - is similar to what I need, but it's solution doesn't work on me.
2)I want to map this with grammar pattern and get the words tag.
Det=the, N(Subject)=man, V=went, N(Object)=home
Is there a way to map this tree with given set tree structures and identify the grammar.
how can I use parse tree to identify Subject, verb, object, the grammar pattern and the generate the target language sentence.
Edited later..
I tried this code and it gives considerable answer. Any suggestions on this code.
sent("(s(np(n(man))) (vp(v(went)) (np(n(home)))))").
whitespace --> [X], { char_type(X, white) ; char_type(X, space) }, whitespace.
whitespace --> [].
char(C) --> [C], { char_type(C, graph), \+ memberchk(C, "()") }.
chars([C|Rest]) --> char(C), chars(Rest).
chars([C]) --> char(C).
term(T) --> chars(C), { atom_chars(T, C) }.
term(L) --> list(L).
list(T) --> "(", terms(T), ")".
terms([]) --> [].
terms([T|Terms]) --> term(T), whitespace, !, terms(Terms).
simplify([s,[np, [n,[Subject]]], [vp,[v,[Verb]],[np,[n,[Object]]]]],Result) :- Result = [Subject,Verb,Object].
Thanks Mathee
the simpler way to do is by means a visit of the tree, 'hardcoded' on the symbols you are interested.
Here is a more generic utility, that uses (=..)/2 to capture a named part of the tree:
part_of(T, S, R) :- T =.. [F|As],
( F = S,
R = T
; member(N, As),
part_of(N, S, R)
).
?- part_of(s(np(det(the), n(man)), vp(v(went), np(n(home)))),np,P).
P = np(det(the), n(man)) ;
P = np(n(home)) ;
false.
It's a kind of member/2, just for trees. BTW I don't understand the first part of your question: why do you want to use phrase/2 on a syntax tree ? Usually a grammar (the first argument to phrase/2) is meant to build a syntax tree from 'raw' characters stream...