Match last occurrence only in perl regex - regex

/1.1/s/1/-/g
I am working on school assignment to reference implementation sed command. I get this string to match "/1/-/". I have experiment
$str =~ m{/[^/]*/[^/]*/}g;
but result is /1.1/s/. How can I get "/1/-/" only
Could somebody help me?


Use
/[^/]*/[^/]*/(?=[^/]*$)
See proof.
EXPLANATION
--------------------------------------------------------------------------------
/ '/'
--------------------------------------------------------------------------------
[^/]* any character except: '/' (0 or more times
(matching the most amount possible))
--------------------------------------------------------------------------------
/ '/'
--------------------------------------------------------------------------------
[^/]* any character except: '/' (0 or more times
(matching the most amount possible))
--------------------------------------------------------------------------------
/ '/'
--------------------------------------------------------------------------------
(?= look ahead to see if there is:
--------------------------------------------------------------------------------
[^/]* any character except: '/' (0 or more
times (matching the most amount
possible))
--------------------------------------------------------------------------------
$ before an optional \n, and the end of
the string
--------------------------------------------------------------------------------
) end of look-ahead

Related

Regex function to match a specific sequence of characters

I'm looking for a regex that would be True only in case that:
it starts with ${ (1 time, $ can only be there one time)
after that any characters or nothing until } is found
This would match:
${
${test
test${test
${$fdsf$
${test}
This would not match:
$${
$${test
${test}test
Hopefully it's clear :)
Is that possible ?

Does that work for you?
(?<!\$)\$\{[^}]*}?$
https://regex101.com/r/g0vhJo/2

Also use
([^$\n]|^)\$\{[^}\n]*}?$
See regex proof.
EXPLANATION
--------------------------------------------------------------------------------
( group and capture to \1:
--------------------------------------------------------------------------------
[^$\n] any character except: '$', '\n'
(newline)
--------------------------------------------------------------------------------
| OR
--------------------------------------------------------------------------------
^ the beginning of the string
--------------------------------------------------------------------------------
) end of \1
--------------------------------------------------------------------------------
\$ '$'
--------------------------------------------------------------------------------
\{ '{'
--------------------------------------------------------------------------------
[^}\n]* any character except: '}', '\n' (newline)
(0 or more times (matching the most amount
possible))
--------------------------------------------------------------------------------
}? '}' (optional (matching the most amount
possible))
--------------------------------------------------------------------------------
$ before an optional \n, and the end of the
string

Regex matches from right instead of left

I don't know if I diagnosed the issue correctly, but it seems the analyzer starts from right to left, instead of from left to right.
My regex is: \/root\/(.+)\/(.+)\/(.+)\/(.+)$, and my trial sentence is irrelevant/root/user/course/exercise/custom/folder/file.txt
The match is correct, but not the groups. I want to get:
group 1: user
group 2: course
group 3: exercise
group 4: custom/folder/file.txt (basically everything that goes after the previous groups).
I'm running this on TS and playing with it on regex101.com (ES set)

Use
\/root\/([^/]+)\/([^/]+)\/([^/]+)\/(.*)$
See proof.
EXPLANATION
--------------------------------------------------------------------------------
\/ '/'
--------------------------------------------------------------------------------
root 'root'
--------------------------------------------------------------------------------
\/ '/'
--------------------------------------------------------------------------------
( group and capture to \1:
--------------------------------------------------------------------------------
[^/]+ any character except: '/' (1 or more
times (matching the most amount
possible))
--------------------------------------------------------------------------------
) end of \1
--------------------------------------------------------------------------------
\/ '/'
--------------------------------------------------------------------------------
( group and capture to \2:
--------------------------------------------------------------------------------
[^/]+ any character except: '/' (1 or more
times (matching the most amount
possible))
--------------------------------------------------------------------------------
) end of \2
--------------------------------------------------------------------------------
\/ '/'
--------------------------------------------------------------------------------
( group and capture to \3:
--------------------------------------------------------------------------------
[^/]+ any character except: '/' (1 or more
times (matching the most amount
possible))
--------------------------------------------------------------------------------
) end of \3
--------------------------------------------------------------------------------
\/ '/'
--------------------------------------------------------------------------------
( group and capture to \4:
--------------------------------------------------------------------------------
.* any character except \n (0 or more times
(matching the most amount possible))
--------------------------------------------------------------------------------
) end of \4
--------------------------------------------------------------------------------
$ before an optional \n, and the end of the
string

How to match urls with 3 slashes with REGEXMATCH function in Goggle Spreadsheets

I have a list of URLS in google spreadsheet, and I'd like to match urls that contain 3 slashes (home page ulrs). I tried to use this formula but it doesn't match correctly
=REGEXMATCH(B2;"^https?:\/\/.*?\.[a-z]{2,6}/$")

Use
=REGEXMATCH(B2;"^https?://[^/]*\.[a-zA-Z]{2,6}/$")
Note [^/]*, zero or more characters different from /.
EXPLANATION
--------------------------------------------------------------------------------
^ the beginning of the string
--------------------------------------------------------------------------------
http 'http'
--------------------------------------------------------------------------------
s? 's' (optional (matching the most amount
possible))
--------------------------------------------------------------------------------
:// '://'
--------------------------------------------------------------------------------
[^/]* any character except: '/' (0 or more times
(matching the most amount possible))
--------------------------------------------------------------------------------
\. '.'
--------------------------------------------------------------------------------
[a-zA-Z]{2,6} any character of: 'a' to 'z', 'A' to 'Z'
(between 2 and 6 times (matching the most
amount possible))
--------------------------------------------------------------------------------
/ '/'
--------------------------------------------------------------------------------
$ before an optional \n, and the end of the
string

Regex help - match one string but not another

I have been using this:
~^\/student-accommodation\/(?:[^\/]+?)\/([^\/]+)\/$
to match for URLs like
/student-accommodation/manchester/ropemaker-court-manchester/
But now I need to edit this regex so it also matches for URLs like the below. All these new URLs will follow the same pattern and add a string that starts with #utm-source. Importantly they won't have another / in them.
/student-accommodation/manchester/ropemaker-court-manchester/#utm_source=afs&utm_medium=email&utm_campaign=ropemakercourt_afs_dec20
But then I don't want the regex to match for URLs like the below:
/student-accommodation/manchester/ropemaker-court-manchester/en-suite/
Can anyone help? I am a novice at regex! Thanks

Use
^\/student-accommodation\/[^\/]+\/([^\/]+)\/(?:#utm_source.*)?$
See proof
Explanation
--------------------------------------------------------------------------------
^ the beginning of the string
--------------------------------------------------------------------------------
\/ '/'
--------------------------------------------------------------------------------
student- 'student-accommodation'
accommodation
--------------------------------------------------------------------------------
\/ '/'
--------------------------------------------------------------------------------
[^\/]+ any character except: '\/' (1 or more
times (matching the most amount possible))
--------------------------------------------------------------------------------
\/ '/'
--------------------------------------------------------------------------------
( group and capture to \1:
--------------------------------------------------------------------------------
[^\/]+ any character except: '\/' (1 or more
times (matching the most amount
possible))
--------------------------------------------------------------------------------
) end of \1
--------------------------------------------------------------------------------
\/ '/'
--------------------------------------------------------------------------------
(?: group, but do not capture (optional
(matching the most amount possible)):
--------------------------------------------------------------------------------
#utm_source '#utm_source'
--------------------------------------------------------------------------------
.* any character except \n (0 or more times
(matching the most amount possible))
--------------------------------------------------------------------------------
)? end of grouping
--------------------------------------------------------------------------------
$ before an optional \n, and the end of the
string

Multiple regex matching within a lookaround

i am trying to do a multiple match within a lookbehind and a look forward
Let's say i have the following string:
$ Hi, this is an example #
Regex: (?<=$).+a.+(?=#)
I am expecting it to return both 'a' within those boundaries, is there a way to do it with only one regex?
Engine: Python

If you can use quantifiers in the lookbehind, use
(?<=\$[^$#]*?)a(?=[^#]*#)
See proof.
Explanation
--------------------------------------------------------------------------------
(?<= look behind to see if there is:
--------------------------------------------------------------------------------
\$ '$'
--------------------------------------------------------------------------------
[^$#]*? any character except: '$' and '#' (0 or more
times (matching the least amount possible))
--------------------------------------------------------------------------------
) end of look-behind
--------------------------------------------------------------------------------
a 'a'
--------------------------------------------------------------------------------
(?= look ahead to see if there is:
--------------------------------------------------------------------------------
[^#]* any character except: '#' (0 or more
times (matching the most amount
possible))
--------------------------------------------------------------------------------
# '#'
--------------------------------------------------------------------------------
) end of look-ahead
PCRE pattern:
(?:\G(?<!^)|\$)[^$]*?\Ka(?=[^#]*#)
See another proof
Explanation
--------------------------------------------------------------------------------
(?: group, but do not capture:
--------------------------------------------------------------------------------
\G where the last m//g left off
--------------------------------------------------------------------------------
(?<! look behind to see if there is not:
--------------------------------------------------------------------------------
^ the beginning of the string
--------------------------------------------------------------------------------
) end of look-behind
--------------------------------------------------------------------------------
| OR
--------------------------------------------------------------------------------
\$ '$'
--------------------------------------------------------------------------------
) end of grouping
--------------------------------------------------------------------------------
[^$#]*? any character except: '$' and '#' (0 or more times
(matching the least amount possible))
--------------------------------------------------------------------------------
\K match reset operator
--------------------------------------------------------------------------------
a 'a'
--------------------------------------------------------------------------------
(?= look ahead to see if there is:
--------------------------------------------------------------------------------
[^#]* any character except: '#' (0 or more
times (matching the most amount
possible))
--------------------------------------------------------------------------------
# '#'
--------------------------------------------------------------------------------
) end of look-ahead