php regex: Alternative to backreference in negative lookbehind
I want to find instances where a captured group does not appear later in the string:
aaaBbb = CccBbb <- format is valid, skip
aaaDddd = CccDddd <- format is valid, skip
aaaEeee = CccFfff <- format is not valid, match this one only
So this matches the lines I don't want to match ( https://regex101.com/r/lon87L/1 )
/^ +w+([A-Z][a-z+]) += +w+1$/mg
I've read on https://www.regular-expressions.info/refadv.html that php doesn't support backreferences inside a negative lookbehind, but other implementations of regex can. So something like this would match the invalid lines that I want to match, but it doesn't work in php:
/^ +w+([A-Z][a-z+]) += +w+(?<!1)$/mg
Is there anything else that would work, other than matching all of three lines and looping through the matches in a php foreach?
php regex negative-lookbehind
asked Nov 15 at 22:00
Redzarf
1,3211731
add a comment |
I want to find instances where a captured group does not appear later in the string:
aaaBbb = CccBbb <- format is valid, skip
aaaDddd = CccDddd <- format is valid, skip
aaaEeee = CccFfff <- format is not valid, match this one only
So this matches the lines I don't want to match ( https://regex101.com/r/lon87L/1 )
/^ +w+([A-Z][a-z+]) += +w+1$/mg
I've read on https://www.regular-expressions.info/refadv.html that php doesn't support backreferences inside a negative lookbehind, but other implementations of regex can. So something like this would match the invalid lines that I want to match, but it doesn't work in php:
/^ +w+([A-Z][a-z+]) += +w+(?<!1)$/mg
Is there anything else that would work, other than matching all of three lines and looping through the matches in a php foreach?
php regex negative-lookbehind
asked Nov 15 at 22:00
Redzarf
1,3211731
Negative lookbehinds require a compile time fixed length. A backreference is a runtime item with variable length. One option is to(?>1(*SKIP)(*FAIL)|w)+and match the backreference. This is probably quicker too.
– sln
Nov 15 at 22:19
You can see it here regex101.com/r/6gfSBi/1 Btw, only the Dot-Net engine supports variable width lookbehinds (including backreferences).
– sln
Nov 15 at 22:22
If it has to be at the EOS, just add a$after the backref regex101.com/r/QuXJLY/1
– sln
Nov 15 at 22:27
add a comment |
I want to find instances where a captured group does not appear later in the string:
aaaBbb = CccBbb <- format is valid, skip
aaaDddd = CccDddd <- format is valid, skip
aaaEeee = CccFfff <- format is not valid, match this one only
So this matches the lines I don't want to match ( https://regex101.com/r/lon87L/1 )
/^ +w+([A-Z][a-z+]) += +w+1$/mg
I've read on https://www.regular-expressions.info/refadv.html that php doesn't support backreferences inside a negative lookbehind, but other implementations of regex can. So something like this would match the invalid lines that I want to match, but it doesn't work in php:
/^ +w+([A-Z][a-z+]) += +w+(?<!1)$/mg
Is there anything else that would work, other than matching all of three lines and looping through the matches in a php foreach?
php regex negative-lookbehind
asked Nov 15 at 22:00
Redzarf
1,3211731
I want to find instances where a captured group does not appear later in the string:
aaaBbb = CccBbb <- format is valid, skip
aaaDddd = CccDddd <- format is valid, skip
aaaEeee = CccFfff <- format is not valid, match this one only
So this matches the lines I don't want to match ( https://regex101.com/r/lon87L/1 )
/^ +w+([A-Z][a-z+]) += +w+1$/mg
I've read on https://www.regular-expressions.info/refadv.html that php doesn't support backreferences inside a negative lookbehind, but other implementations of regex can. So something like this would match the invalid lines that I want to match, but it doesn't work in php:
/^ +w+([A-Z][a-z+]) += +w+(?<!1)$/mg
Is there anything else that would work, other than matching all of three lines and looping through the matches in a php foreach?
php regex negative-lookbehind
php regex negative-lookbehind
asked Nov 15 at 22:00
Redzarf
1,3211731
asked Nov 15 at 22:00
Redzarf
1,3211731
asked Nov 15 at 22:00
Redzarf
1,3211731
asked Nov 15 at 22:00
Redzarf
1,3211731
asked Nov 15 at 22:00
Redzarf
1,3211731
1,3211731
Negative lookbehinds require a compile time fixed length. A backreference is a runtime item with variable length. One option is to(?>1(*SKIP)(*FAIL)|w)+and match the backreference. This is probably quicker too.
– sln
Nov 15 at 22:19
You can see it here regex101.com/r/6gfSBi/1 Btw, only the Dot-Net engine supports variable width lookbehinds (including backreferences).
– sln
Nov 15 at 22:22
If it has to be at the EOS, just add a$after the backref regex101.com/r/QuXJLY/1
– sln
Nov 15 at 22:27
add a comment |
Negative lookbehinds require a compile time fixed length. A backreference is a runtime item with variable length. One option is to(?>1(*SKIP)(*FAIL)|w)+and match the backreference. This is probably quicker too.
– sln
Nov 15 at 22:19
You can see it here regex101.com/r/6gfSBi/1 Btw, only the Dot-Net engine supports variable width lookbehinds (including backreferences).
– sln
Nov 15 at 22:22
If it has to be at the EOS, just add a$after the backref regex101.com/r/QuXJLY/1
– sln
Nov 15 at 22:27
Negative lookbehinds require a compile time fixed length. A backreference is a runtime item with variable length. One option is to
(?>1(*SKIP)(*FAIL)|w)+ and match the backreference. This is probably quicker too.– sln
Nov 15 at 22:19
Negative lookbehinds require a compile time fixed length. A backreference is a runtime item with variable length. One option is to
(?>1(*SKIP)(*FAIL)|w)+ and match the backreference. This is probably quicker too.– sln
Nov 15 at 22:19
You can see it here regex101.com/r/6gfSBi/1 Btw, only the Dot-Net engine supports variable width lookbehinds (including backreferences).
– sln
Nov 15 at 22:22
You can see it here regex101.com/r/6gfSBi/1 Btw, only the Dot-Net engine supports variable width lookbehinds (including backreferences).
– sln
Nov 15 at 22:22
If it has to be at the EOS, just add a
$ after the backref regex101.com/r/QuXJLY/1– sln
Nov 15 at 22:27
If it has to be at the EOS, just add a
$ after the backref regex101.com/r/QuXJLY/1– sln
Nov 15 at 22:27
add a comment |
2 Answers
2
active
oldest
votes
Try using using a negative lookahead instead of a negative lookbehind. It works equally well, plus it works in PHP.
^ +w+([A-Z][a-z]+) += +(?!w+1).*$
regex101 demo
PHP demo
answered Nov 15 at 22:29
Davіd
3,62541635
add a comment |
One option would be to, right before each repeated w after the =, use negative lookahead for 1$:
^ +w+([A-Z][a-z]+) += +(?:(?!1$)w)+$
^^^^^^^^^^^^^^
https://regex101.com/r/lon87L/2
But that only excludes a match if the backreference occurs right at the end of the string. If you want to ensure that the previously matched phrase doesn't occur anywhere within the final ws, just remove the $ from inside the repeated group:
^ +w+([A-Z][a-z]+) += +(?:(?!1)w)+$
^
https://regex101.com/r/lon87L/3
answered Nov 15 at 22:07
CertainPerformance
75.1k143659
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
Try using using a negative lookahead instead of a negative lookbehind. It works equally well, plus it works in PHP.
^ +w+([A-Z][a-z]+) += +(?!w+1).*$
regex101 demo
PHP demo
answered Nov 15 at 22:29
Davіd
3,62541635
add a comment |
Try using using a negative lookahead instead of a negative lookbehind. It works equally well, plus it works in PHP.
^ +w+([A-Z][a-z]+) += +(?!w+1).*$
regex101 demo
PHP demo
answered Nov 15 at 22:29
Davіd
3,62541635
add a comment |
Try using using a negative lookahead instead of a negative lookbehind. It works equally well, plus it works in PHP.
^ +w+([A-Z][a-z]+) += +(?!w+1).*$
regex101 demo
PHP demo
answered Nov 15 at 22:29
Davіd
3,62541635
Try using using a negative lookahead instead of a negative lookbehind. It works equally well, plus it works in PHP.
^ +w+([A-Z][a-z]+) += +(?!w+1).*$
regex101 demo
PHP demo
answered Nov 15 at 22:29
Davіd
3,62541635
edited Nov 15 at 22:45
answered Nov 15 at 22:29
Davіd
3,62541635
answered Nov 15 at 22:29
Davіd
3,62541635
answered Nov 15 at 22:29
Davіd
3,62541635
3,62541635
add a comment |
add a comment |
One option would be to, right before each repeated w after the =, use negative lookahead for 1$:
^ +w+([A-Z][a-z]+) += +(?:(?!1$)w)+$
^^^^^^^^^^^^^^
https://regex101.com/r/lon87L/2
But that only excludes a match if the backreference occurs right at the end of the string. If you want to ensure that the previously matched phrase doesn't occur anywhere within the final ws, just remove the $ from inside the repeated group:
^ +w+([A-Z][a-z]+) += +(?:(?!1)w)+$
^
https://regex101.com/r/lon87L/3
answered Nov 15 at 22:07
CertainPerformance
75.1k143659
add a comment |
One option would be to, right before each repeated w after the =, use negative lookahead for 1$:
^ +w+([A-Z][a-z]+) += +(?:(?!1$)w)+$
^^^^^^^^^^^^^^
https://regex101.com/r/lon87L/2
But that only excludes a match if the backreference occurs right at the end of the string. If you want to ensure that the previously matched phrase doesn't occur anywhere within the final ws, just remove the $ from inside the repeated group:
^ +w+([A-Z][a-z]+) += +(?:(?!1)w)+$
^
https://regex101.com/r/lon87L/3
answered Nov 15 at 22:07
CertainPerformance
75.1k143659
add a comment |
One option would be to, right before each repeated w after the =, use negative lookahead for 1$:
^ +w+([A-Z][a-z]+) += +(?:(?!1$)w)+$
^^^^^^^^^^^^^^
https://regex101.com/r/lon87L/2
But that only excludes a match if the backreference occurs right at the end of the string. If you want to ensure that the previously matched phrase doesn't occur anywhere within the final ws, just remove the $ from inside the repeated group:
^ +w+([A-Z][a-z]+) += +(?:(?!1)w)+$
^
https://regex101.com/r/lon87L/3
answered Nov 15 at 22:07
CertainPerformance
75.1k143659
One option would be to, right before each repeated w after the =, use negative lookahead for 1$:
^ +w+([A-Z][a-z]+) += +(?:(?!1$)w)+$
^^^^^^^^^^^^^^
https://regex101.com/r/lon87L/2
But that only excludes a match if the backreference occurs right at the end of the string. If you want to ensure that the previously matched phrase doesn't occur anywhere within the final ws, just remove the $ from inside the repeated group:
^ +w+([A-Z][a-z]+) += +(?:(?!1)w)+$
^
https://regex101.com/r/lon87L/3
answered Nov 15 at 22:07
CertainPerformance
75.1k143659
answered Nov 15 at 22:07
CertainPerformance
75.1k143659
answered Nov 15 at 22:07
CertainPerformance
75.1k143659
answered Nov 15 at 22:07
CertainPerformance
75.1k143659
75.1k143659
add a comment |
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Negative lookbehinds require a compile time fixed length. A backreference is a runtime item with variable length. One option is to
(?>1(*SKIP)(*FAIL)|w)+and match the backreference. This is probably quicker too.– sln
Nov 15 at 22:19
You can see it here regex101.com/r/6gfSBi/1 Btw, only the Dot-Net engine supports variable width lookbehinds (including backreferences).
– sln
Nov 15 at 22:22
If it has to be at the EOS, just add a
$after the backref regex101.com/r/QuXJLY/1– sln
Nov 15 at 22:27