问正则表达式以匹配单个页面或页面范围？

EN

/^(\d+)(?:-(\d+))?$/ && $1 < $2;

m{                     # /../ is shorthand for m/../
    \A                 # beginning of string
    (\d+)              # first number
    (?:-               # a non-capturing group starting with '-'...
        (\d+)          #     second number
        (?(?{$1>=$2})  #     if first number is >= second number
            (?!))      #         fail this match
    )?                 # ...this group is optional
    \Z                 # end of string
}x                     # /x tells Perl to allow spaces and comments inside regex

/^\s*
    (\d+) (?:\s*-\s* (\d+))?
    (?:\s*,\s* (\d+) (?:\s*-\s* (\d+))?)*
\s*$/x

m{
    \A\s*                              # start of string, spaces
    (?{{$min = 0}})                    # initialize min := 0
    (?&RANGE) (?:\s*,\s* (?&RANGE))*   # a range, many (comma, range)
    \s*\Z                              # spaces, end of string

    (?(DEFINE)                         # define the named groups:
        (?<NUMBER>                     #   number :=
            (\d*)                      #     a sequence of digits
            (?(?{$min < $^N})          #     if this number is greater than min
                (?{{$min = $^N}})      #       then update min
                | (?!)))               #       else fail
        (?<RANGE>                      #   range :=
            (?&NUMBER)                 #     a number
            (?:\s*-\s* (?&NUMBER))?))  #     maybe a hyphen and another number
}x

^\d+(?:-\d+)?$

/^(\d+)(-(\d+))?/

if $1 <= $3