The RegEx:
^([0-9\.]+)\Q|\E([^\Q|\E])\Q|\E
does not match the string:
1203730263.912|12.66.18.0|
Why?
From PHP docs,
\Q and \E can be used to ignore regexp metacharacters in the pattern.
For example:
\w+\Q.$.\E$ will match one or more word characters, followed by literals .$. and anchored at the end of the string.
And your regex should be,
^([0-9\.]+)\Q|\E([^\Q|\E]*)\Q|\E
OR
^([0-9\.]+)\Q|\E([^\Q|\E]+)\Q|\E
You forget to add + after [^\Q|\E]. Without +, it matches single character.
DEMO
Explanation:
^ Starting point.
([0-9\.]+) Captures digits or dot one or more times.
\Q|\E In PCRE, \Q and \E are referred to as Begin sequence. Which treats any character literally when it's included in that block. So | symbol in that block tells the regex engine to match a literal |.
([^\Q|\E]+) Captures any character not of | one or more times.
\Q|\E Matches a literal pipe symbol.
The accepted answer seems somewhat incorrect so I wanted to address this for future readers.
If you did not already know, using \Q and \E ensures that any character between \Q ... \E will be matched literally, not interpreted as a metacharacter by the regular expression engine.
First and most important, \Q and \E is NOT usable within a bracketed character class [].
[^\Q|\E] # Incorrect
[^|] # Correct
Secondly, you do not follow that class with a quantifier. Using this, the correct syntax would be:
^([0-9.]+)\Q|\E([^|]+)\Q|\E
Although, it is much simpler to write this out as:
^([0-9.]+)\|([^|]+)\|
Related
With regular expression I would like to get all characters between round brackets, but \( and \) characters should be also included in the result.
Examples:
input: fo(ob)a)r
output: ob
input: foo(bar\(qwerty\))baz
output: bar\(qwerty\)
This is what I used for finding text between brackets:
(?<=\()([^\s\(\)]+)(?=\)), but I can't make exceptions for brackets preceded by \.
You could do something like this :
.*(?<!\\)\((.*?)(?<!\\)\)
Basically, it matches as many characters as possible until it sees an open parenthesis without a backslash (using a negative lookbehind), then groups the next matching characters until a closing parenthesis (still without a backslash).
Note that this regex may not work properly if you escape the backslashes.
Example : https://regex101.com/r/BqVKZp/1
This regex works for both your examples, without any lookaheads and lookbehinds:
\((.+[^\\])\)
A U flag is needed.
Im trying to find files that are looking like this:
access_log-20160101
access_log-20160304
...
with perl regex i came up with something like this:
/^access_log-\d{8}$/
But im not sure about the "_" and the "-". are these metacharacter?
What is the expression for this?
i read that "_" in regex is something like \w, but how do i use them in my exypression?
/^access\wlog-\d{8}$/ ?
Underscore (_) is not a metacharacter and does not need to be quoted (though it won't change anything if you quote it).
Hyphen (-) IS a metacharacter that defines the range between two symbols inside a bracketed character class. However, in this particular position, it will be interpreted verbatim and doesn't need quoting since it is not inside [] with a symbol on both sides.
You can use your regexp as is; hyphens (-) might need quoting if your format changes in future.
Your regex pattern is exactly right
Neither underscore _ nor hyphen - need to be escaped. Outside a square-bracketed character class, the twelve Perl regex metacharacters are
Brackets ( ) [ {
Quantifiers * + ?
Anchors ^ $
Alternator |
Wild character .
The escape itself \
and only these must be escaped
If the pattern of your file names doesn't vary from what you have shown then the pattern that you are using
^access_log-\d{8}$
is correct, unless you need to validate the date string
Within a character class like [A-F] you must escape the hyphen if you want it to be interpreted literally. As it stands, that class is the equivalent to [ABCDEF]. If you mean just the three characters A, - or F then [A\-F] will do what you want, but it is usual to put the hyphen at the start or end of the class list to make it unambiguous. [-AF] and [AF-] are the same as [A\-F] and rather more readable
I am using Notepad++ to remove some unwanted strings from the end of a pattern and this for the life of me has got me.
I have the following sets of strings:
myApp.ComboPlaceHolderLabel,
myApp.GridTitleLabel);
myApp.SummaryLabel + '</b></div>');
myApp.NoneLabel + ')') + '</label></div>';
I would like to leave just myApp.[variable] and get rid of, e.g. ,, );, + '...', etc.
Using Notepad++, I can match the strings themselves using ^myApp.[a-zA-Z0-9].*?\b (it's a bit messy, but it works for what I need).
But in reality, I need negate that regex, to match everything at the end, so I can replace it with a blank.
You don't need to go for negation. Just put your regex within capturing groups and add an extra .*$ at the last. $ matches the end of a line. All the matched characters(whole line) are replaced by the characters which are present inside the first captured group. .
matches any character, so you need to escape the dot to match a literal dot.
^(myApp\.[a-zA-Z0-9].*?\b).*$
Replacement string:
\1
DEMO
OR
Match only the following characters and then replace it with an empty string.
\b[,); +]+.*$
DEMO
I think this works equally as well:
^(myApp.\w+).*$
Replacement string:
\1
From difference between \w and \b regular expression meta characters:
\w stands for "word character", usually [A-Za-z0-9_]. Notice the inclusion of the underscore and digits.
(^.*?\.[a-zA-Z]+)(.*)$
Use this.Replace by
$1
See demo.
http://regex101.com/r/lU7jH1/5
What do these mean?
qr{^\Q$1\E[a-zA-Z0-9_\-]*\Q$2\E$}i
qr{^[a-zA-Z0-9_\-]*\Q$1\E$}i
If $pattern is a Perl regular expression, what is $identity in the code below?
$identity =~ $pattern;
When the RHS of =~ isn't m//, s/// or tr///, a match operator (m//) is implied.
$identity =~ $pattern;
is the same as
$identity =~ /$pattern/;
It matches the pattern or pre-compiled regex $pattern (qr//) against the value of $identity.
The binding operator =~ applies a regex to a string variable. This is documented in perldoc perlop
The \Q ... \E escape sequence is a way to quote meta characters (also documented in perlop). It allows for variable interpolation, though, which is why you can use it here with $1 and $2. However, using those variables inside a regex is somewhat iffy, because they themselves are defined during the use of a capture inside a regex.
The character class bracket [ ... ] defines a range of characters which it will match. The quantifier that follows it * means that particular bracket must match zero or more times. The dashes denote ranges, such as a-z meaning "from a through z". The escaped dash \- means a literal dash.
The ^ and $ (the dollar sign at the end) denotes anchors, beginning and end of string respectively. The modifier i at the end means the match is case insensitive.
In your example, $identity is a variable that presumably contains a string (or whatever it contains will be converted to a string).
The perlre documentation is your friend here. Search it for unfamiliar regex constructs.
A detailed explanation is below, but it is so hairy that I wonder whether using a module such as Text::Balanced would be a superior approach.
The first pattern matches possibly empty delimited strings, and the delimiters are in $1 and $2, which we do not know until runtime. Say $1 is ( and $2 is ), then the first pattern matches strings of the form
()
(a)
(9)
(abcABC_012-)
and so on …
The second pattern matches terminated strings, where the terminator is in $1—also not known until runtime. Assuming the terminator is ], then the second pattern matches strings of the form
]
a]
Aa9a_9]
Using \Q...\E around a pattern removes any special regex meaning from the characters inside, as documented in perlop:
For the pattern of regex operators (qr//, m// and s///), the quoting from \Q is applied after interpolation is processed, but before escapes are processed. This allows the pattern to match literally (except for $ and #). For example, the following matches:
'\s\t' =~ /\Q\s\t/
Because $ or # trigger interpolation, you'll need to use something like /\Quser\E\#\Qhost/ to match them literally.
The patterns in your question do want to trigger interpolation but do not want any regex metacharacters to have special meaning, as with parentheses and square brackets above that are meant to match literally.
Other parts:
Circumscribed brackets delimit a character class. For example, [a-zA-Z0-9_\-] matches any single character that is upper- or lowercase A through Z (but with no accents or other extras), zero through nine, underscore, or hyphen. Note that the hyphen is escaped at the end to emphasize that it matches a literal hyphen rather and does not specify part of a range.
The * quantifier means match zero or more of the preceding subpattern. In the examples from your question, the star repeats character classes.
The patterns are bracketed with ^ and $, which means an entire string must match rather than some substring to succeed.
The i at the end, after the closing curly brace, is a regex switch that makes the pattern case-insensitive. As TLP helpfully points out in the comment below, this makes the delimiters or terminators match without regard to case if they contain letters.
The expression $identity =~ $pattern tests whether the compiled regex stored in $pattern (created with $pattern = qr{...}) matches the text in $identity. As written above, it is likely being evaluated for its side effect of storing capture groups in $1, $2, etc. This is a red flag. Never use $1 and friends unconditionally but instead write
if ($identity =~ $pattern) {
print $1, "\n"; # for example
}
I am a beginner of perl scripting.
I know hyphen (-) is used to specify the range.
But what if it is mentioned in the beginning of the expression?
Example:
if ($_ =~ /-\n/)
//do something
How to interpret the above code?
"if the parameter is equal to a range of newline" ?
(No, that is weird understanding :-/)
Please help.
Outside of [] - means "-" as far as I know, it only indicates a range within a [] block.
Here is a more complete answer I found
How to match hyphens with Regular Expression? (look at the second answer)
So the expression should match a - followed by a newline or line ending with -
The pattern will match hyphens "-" followed by a newline \n.
The hyphen is treated as a range operator inside character classes, as explained in perldoc perlrequick:
The special character '-' acts as a range operator within character
classes, so that the unwieldy [0123456789] and [abc...xyz] become
the svelte [0-9] and [a-z] :
/item[0-9]/; # matches 'item0' or ... or 'item9'
/[0-9a-fA-F]/; # matches a hexadecimal digit
If '-' is the first or last character in a character class, it is
treated as an ordinary character.
This means:
If there is a hyphen immediately followed by a newline-character, no matter where this pair of characters is located inside the string.