regex101: nested if..elsif..else..endif

Group nested(?P<nested> \b if \b (?P<if>(?>.?(?>(?P>nested))?)*?) (?: \b elsif \b (?P<elsif>(?>.?(?>(?P>nested))?)*?) )? (?: \b else \b (?P<else>(?>.?(?>(?P>nested))?)*?) )? \b endif \b )?

?repeats the group contents below at most once:

\ban ASCII word boundary

if the literal text if (case insensitive)

\ban ASCII word boundary

Group if(?P<if>(?>.?(?>(?P>nested))?)*?)

Atomic Group(?>.?(?>(?P>nested))?)*?

*?repeats the group contents below any number of times:

.?optionally matches any character

Atomic Group(?>(?P>nested))?

?repeats the group contents below at most once:

(?P>nested)calls group nested as a subroutine

Non-Capturing Group(?: \b elsif \b (?P<elsif>(?>.?(?>(?P>nested))?)*?) )?

?repeats the group contents below at most once:

\ban ASCII word boundary

elsif the literal text elsif (case insensitive)

\ban ASCII word boundary

Group elsif(?P<elsif>(?>.?(?>(?P>nested))?)*?)

Atomic Group(?>.?(?>(?P>nested))?)*?

*?repeats the group contents below any number of times:

.?optionally matches any character

Atomic Group(?>(?P>nested))?

?repeats the group contents below at most once:

(?P>nested)calls group nested as a subroutine

Non-Capturing Group(?: \b else \b (?P<else>(?>.?(?>(?P>nested))?)*?) )?

?repeats the group contents below at most once:

\ban ASCII word boundary

else the literal text else (case insensitive)

\ban ASCII word boundary

Group else(?P<else>(?>.?(?>(?P>nested))?)*?)

Atomic Group(?>.?(?>(?P>nested))?)*?

*?repeats the group contents below any number of times:

.?optionally matches any character

Atomic Group(?>(?P>nested))?

?repeats the group contents below at most once:

(?P>nested)calls group nested as a subroutine

\ban ASCII word boundary

endif the literal text endif (case insensitive)

\ban ASCII word boundary

Global pattern flags

i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters

x modifier: extended. Ignores unescaped whitespace and comments outside character classes

s modifier: single line. Allows a dot to match line terminators

Search reference

Regular Expression

(?P<nested>
  \b if \b
    (?P<if>(?>.?(?>(?P>nested))?)*?)
  (?:
    \b elsif \b
      (?P<elsif>(?>.?(?>(?P>nested))?)*?)
    )?
  (?:
    \b else \b
      (?P<else>(?>.?(?>(?P>nested))?)*?)
    )?
  \b endif \b
)?

Test String
New

if
  1
  if
    2
  elsif
    2
  else
    2
    if
      3
    endif
    2
  endif
  1
  if
    2
  else
    2
  endif
  1
elsif
  1_elsif1_
elsif
  1_elsif2_
else
  1_else_
endif

Regular Expression

Test StringNew

Test String
New