Nginx location block section have a search order, a modifier, an implicit match type and an implicit switch to whether stop the search on match or not. the following array describe it for regex.
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# Search-Order Modifier Description Match-Type Stops-search-on-match
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# 1st = The URI must match the specified pattern exactly Simple-string Yes
# 2nd ^~ The URI must begin with the specified pattern Simple-string Yes
# 3rd (None) The URI must begin with the specified pattern Simple-string No
# 4th ~ The URI must be a case-sensitive match to the specified Rx Perl-Compatible-Rx Yes (first match)
# 4th ~* The URI must be a case-insensitive match to the specified Rx Perl-Compatible-Rx Yes (first match)
# N/A @ Defines a named location block. Simple-string Yes
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Capturing group, expression evaluation () are supported, this example location ~ ^/(?:index|update)$ match url ending with example.com/index and example.com/update
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# () : Group/Capturing-group, capturing mean match and retain/output/use what matched
# the patern inside (). the default bracket mode is "capturing group" while (?:)
# is a non capturing group. example (?:a|b) match a or b in a non capturing mode
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# ?: : Non capturing group
# ?= : Positive look ahead
# ?! : is for negative look ahead (do not match the following...)
# ?<= : is for positive look behind
# ?<! : is for negative look behind
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Not to confuse with the regex slash \, In nginx the forward slash / is used to match any sub location including none example location /. In the context of regex support the following explanation apply
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# / : It doesn't actually do anything. In Javascript, Perl and some other languages,
# it is used as a delimiter character explicitly for regular expressions.
# Some languages like PHP use it as a delimiter inside a string,
# with additional options passed at the end, just like Javascript and Perl.
# Nginx does not use delimiter, / can be escaped with \/ for code portability
# purpose BUT this is not required for nginx / are handled literally
# (don't have other meaning than /)
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The first purpose of the regex special character \ is meant to escape the next character; But note that in most case \ followed by a character have a different meaning, a complete list is available here.
Nginx does not require escaping the forward slash / it does not either deny escaping it like we could escape any other character. and thus \/ is translated/matching /. One purpose of escaping forward slashes in the context of nginx could be for code portability.
Here is a non exhaustive list of regex expression that can be used
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# ~ : Enable regex mode for location (in regex ~ mean case-sensitive match)
# ~* : case-insensitive match
# | : Or
# () : Match group or evaluate the content of ()
# $ : the expression must be at the end of the evaluated text
# (no char/text after the match) $ is usually used at the end of a regex
# location expression.
# ? : Check for zero or one occurrence of the previous char ex jpe?g
# ^~ : The match must be at the beginning of the text, note that nginx will not perform
# any further regular expression match even if an other match is available
# (check the table above); ^ indicate that the match must be at the start of
# the uri text, while ~ indicates a regular expression match mode.
# example (location ^~ /realestate/.*)
# Nginx evaluation exactly this as don't check regexp locations if this
# location is longest prefix match.
# = : Exact match, no sub folders (location = /)
# ^ : Match the beginning of the text (opposite of $). By itself, ^ is a
# shortcut for all paths (since they all have a beginning).
# .* : Match zero, one or more occurrence of any char
# \ : Escape the next char
# . : Any char
# * : Match zero, one or more occurrence of the previous char
# ! : Not (negative look ahead)
# {} : Match a specific number of occurrence ex. [0-9]{3} match 342 but not 32
# {2,4} match length of 2, 3 and 4
# + : Match one or more occurrence of the previous char
# [] : Match any char inside
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location ~ ^/(?:index)\.php(?:$|/)
location ~ ^\/(?:core\/img\/background.png|core\/img\/favicon.ico)(?:$|\/)
location ~ ^/(?:index|core/ajax/update|ocs/v[12]|status|updater/.+|oc[ms]-provider/.+)\.php(?:$|/)