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regex and robots.txt

 [1/3] from: hallvard:ystad:oops-as:no at: 3-Aug-2004 13:54

Hi folks, I'm thinking about implementing a sort of robots.txt version 2 with regex for the rix robot. I need to give certain directions of my own for a number of sites, and I wish to use robots.txt files to feed to the bot. Only with regular expressions in them. I've been looking for others' work on this - surely, someone must have thought about using regular expressions in robots.txt files! I found documents like[Frumkin--Excite--html], but nothing very specific. Does anyone know about efforts that have already been done or work that I should see before going deeper into this? And about regular expressions: is there a rebol script that handles them somewhere, or do I have to write my own? I searched, but didn't find anything. (And I couldn't search with rix, because the db has grown too big for my disc. So for the moment, the database is down, and rix doesn't work. I either have to buy some more disc space for the server or I have to look into removing doubles from the index pretty quickly!) Any thoughts or tips on these subjects will be much appreciated. Thanks. HY

 [2/3] from: greggirwin:mindspring at: 3-Aug-2004 9:20

Hi Hallvard, I don't know anything about robots.txt; Sunanda does, but I don't know if he can help with your specific question. He did a lot of research on them for I believe. On RegExs, I can be a little more help. I've done a very simple pattern matcher, and have a lot of notes about doing a real regex engine, but it isn't a small task, so it only happens in bits and pieces. I have a new reason to pursue it (the *nix-sh project to emulate *nix commands), now I just need the time. Any input people have on what's important (e.g. pattern matching, backreferences, substitution) would be great. My %like.r module is below. The syntax emulates the VB Like operator, so it's not nearly complete compared to the regex engine used in perl, Python, et al. I was going to try building an interface to the PCRE DLL, but their interface is a bit odd and I haven't spent time trying to make that work. -- Gregg REBOL [ Title: "VB Like Operator Module" Date: 10-Sep-2003 Version: 0.0.3 File: %like.r Author: "Gregg Irwin" Email: [greggirwin--acm--org] Purpose: { The LIKE? function is a first crack at something like VB's Like operator. i.e. a *very* simple RegEx engine. The real purpose was to help me get acquainted with parse. } Comment: { A hyphen (=96) can appear either at the beginning (after an exclamation point if one is used) or at the end of charlist to match itself. In any other location, the hyphen is used to identify a range of characters. When a range of characters is specified, they must appear in ascending sort order (from lowest to highest). [A-Z] is a valid pattern, but [Z-A] is not. The character sequence [] is considered a zero-length string (""). * Zero or more characters ? Any single character # Any single digit [list] Any single char in list (character class) [!list] Any single char not in list Meta chars, except "]", can be used in character classes. "]" can be used by itself, as a regular char, but not in a character class. } History: [ 0.0.1 [03-Sep-2001 "Initial Release." Gregg] 0.0.2 [19-Mar-2002 "Fixed negated char class syntax" Gregg] 0.0.3 [10-Sep-2003 {Rediscovered this and beefed up the char group syntax so it matches the VB spec better. Still in progress though.} {Renamed some things too.} {Cleaned things up (a little) and reorganized.} Gregg ] ] ] vb-like-op: make object! [ any-char: complement charset "" digit: charset [#"0" - #"9"] non-digit: complement digit any-single-digit: [1 digit] any-single-char: 'skip ; [1 any-char] ;any-multi-char: [any any-char] ;any-multi-char-to: [any any-char to] wild-chars: charset "*?![#" non-wild-chars: complement wild-chars valid-group-chars: complement charset "]" to-next-real-char: 'thru to-end: [to end] expand-pattern: func [ {Convert a VB Like operator spec into a set of PARSE rules.} pattern [string!] /local plain-chars dig star any-one char-group emit tmp result ][ emit: func [arg][ ; OK, this is ugly. If you put *[ in your pattern, it causes ; problems because * = thru (right now) and you can't say ; "thru bitset!" in a parse rule. So, what I do in that case ; is remove the thru and replace it with something I think ; will work. either all [ not empty? result 'to-next-real-char = last result bitset! = type? arg ][ change back tail result reduce ['any complement arg arg] ][ append result arg ] ] plain-chars: [copy tmp some non-wild-chars (emit copy tmp)] dig: ["#" (emit 'any-single-digit)] star: ["*" (emit 'to-next-real-char)] any-one: ["?" (emit 'any-single-char)] char-group: [ "[" copy tmp some valid-group-chars "]" (emit make-group-charset tmp) ] result: copy [] parse/all pattern [ some [char-group | plain-chars | dig | star | any-one] ] ; If the last thing in our pattern is thru, it won't work so we ; remove the trailing thru and replace it with "to end". if (last result) =? 'to-next-real-char [ change back tail result 'to-end ] result ] set 'like? func [ "Emulates the VB Like operator." string [any-string!] "The string you want to check" pattern [any-string!] "The pattern you want to check the string against" ][ parse/all string dbg: expand-pattern pattern ] make-group-charset: func [ {Take a char-group spec and convert it to a charset.} string /local add-group-char add-group-range dash non-dash rules group-chars char char-1 char-2 comp result ][ add-group-char: func [char][ if not none? char [append first group-chars char] ] add-group-range: func [char-1 char-2][ append group-chars reduce [to-char char-1 '- to-char char-2] ] dash: charset "-" non-dash: complement dash rules: [ [copy char opt #"!" (comp: char)] [copy char opt dash (add-group-char char)] some [ copy char-1 non-dash dash copy char-2 non-dash (add-group-range char-1 char-2) | copy char non-dash (add-group-char char) ] [copy char opt dash (add-group-char char)] end ] group-chars: reduce [copy ""] parse string rules ;print mold group-chars result: charset group-chars either comp [complement result][result] ] ; "ABCa-z!012" in PARSE rules is ["ABC" #"a" - #"z" "!012"] ] test: on if test [ test-like: func [ str [string!] pat [string!] /expect expected /show /local result ][ ;print ["Parse: " tab remold vb-like-op/expand-pattern pat] result: like? str pat if show [ print ["Str: " tab str] print ["RegEx: " tab pat] print ["Result:" tab result] print ["Parse: " tab mold vb-like-op/expand-pattern pat] prin newline ] if all [expect result <> expected] [ print [ "^/TEST FAILED!^/" tab str newline tab pat newline tab "Returned:" result newline ] ] ] test-data: reduce [ "abc_()!@^#%_def`=FFz" "abc*def?=FF[xyz]" true "abc_defx" "abc*def[xyz]" true "abc_defx" "abc?def[xyz]" true "abc__defx" "abc??def[!xyz]" false "abc__defx" "abc??def[xyz]" true "abc_defx" {abc?def[!x-z]} false "abc_defx" {abc?def[x-z]} true "abc_defx" {abc?def[!x-z]} false "abc_defx" {abc?def[x-z]} true "abcdxxxxxx" "abc?*" true "avbcvz" "a*z" true "12345_xxx" "*_*" true "filename.txtdfdf" "*.txt*" true "abcdefg" "ab*f[ghi]" true "]ab*&&&fg=FF?$^^^- `~=A8019[" "]ab[*]*f[ghi]=FF[?]?*`~[=A9=BB=A8=A7]###[[]" true "]ab*&&&fg=FF?$^^^- `~=A8019[" "]ab[*]*f[ghi]=FF[?]?*^- ??![=A9=BB=A7]###[[]" false "Gregg 12340 Irwin" "* ####*" true " 12340" "* ####*" true "Gregg 123400" "* ####*" true " 12340 Irwin" "* ####*" true "Looking for [ in text" "Looking for?[[]*" true "Looking for [ in text" "*[[]*" true "Looking for ] in text" "*[[]*" false ] foreach [str pat result] test-data [ test-like/expect str pat result ;/show ] print "Tests complete." halt ]

 [3/3] from: SunandaDH::aol::com at: 3-Aug-2004 15:51

> I'm thinking about implementing a sort of robots.txt version 2 with regex > for the rix robot. I need to give certain directions of my own for a
> of sites, and I wish to use robots.txt files to feed to the bot. Only
> regular expressions in them.
The main problem here is that a robots.txt with REs is unlikely to validate. Given that there are any number of badly written spiders out there that mis-read or mis-parse robots.txt already, I'd be unhappy about deploying a robots.txt that did not validate -- it may confuse well-meaning bots. (Having said that,'s robots.txt does have the non-standard crawl-delay parameter to placate msnbot.....If Rixbot was as big as Microsoft, we might look at a non-standard entry for you too :-) ). One other approach: Consider looking for a rixbot-robots.txt file that contains the specific rules for rixbot. Rixbot-friendly sites would have to create such a file; give us a compelling reason, and I'm sure we would. One other thought: why RE? Why not parse-friendly BNF? Sunanda.