Simple regex question
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From: Janis Papanagnou on 24 Jan 2010 08:57 Stephane CHAZELAS wrote: > 2010-01-24, 04:02(+01), Janis Papanagnou: > [...] >> Frankly, I've never used an old UNIX edition 6 bourne shell and don't know >> how the case statement worked at that time, or whether the case statement >> was existing at all. [...] ....or weather the bourne shell existed at all. > Again, there was no Bourne shell in V6, the Bourne shell was > first released in V7. V6's sh was the Thomson shell. Thanks for clarifying. My UNIX time began later, somewhere between Edition 7 and Sys V, and I've never used Edition 6 or have knowledge about details of that ancient UNIX release; which is what I meant to say above. Janis
From: Icarus Sparry on 24 Jan 2010 17:19 On Sun, 24 Jan 2010 14:23:59 +0100, Janis Papanagnou wrote: > Stephane CHAZELAS wrote: >> 2010-01-24, 06:11(+01), Janis Papanagnou: >>> Seebs wrote: >>>> I'm not sure that even ksh can do everything posix REs can. >>> I am confident and quite sure it does. Vice versa; I think the regexp >>> library will at least have problems emulating ksh's !(...) >>> construct. Ever tried? In general you'll get extremely bulky results >>> here! But the class of languages (regular expressions) is the same, >>> anyway.[*] >>> >>> [*] N.B. Newer ksh's also support back-references in their >>> expressions, so strictly speeking, with that feature, they exceed the >>> Chomsky-3 grammar class as well (analogous to other libraries with >>> backreference extensions). >> [...] >> >> Recent versions of AT&T ksh can also convert globbing patterns to >> regular expressions (a AT&T variant thereof): >> >> $ ksh -c 'printf "%R\n" "!(...)"' >> ^(\.\.\.)!$ > > I didn't knew that ! were a regular expression meta operator in regexp. > > The ! _regexp_ meta operator does not seem to produce results on my box. > > $ ls > hello hello world helloworld regexp world $ ls !(hello) > hello world helloworld regexp world $ ksh -c 'printf "%R\n" > "!(hello)"' > ^(hello)!$ > $ ls | egrep '^(hello)!$' > ### nothing matched ### > > It works well with the known operators + and * etc. resp. +(...) *(...) > etc. > > Still interested in an regexp expression conforming to !(...) ext. glob. The grep from AST will handle this '^(hello)!$' if you give it a -X flag to enable the augmented expressions. An instant thought on matching !(hello) with a RE, this is ^([^h].*|h[^e].*|he[^l].*|hel[^l].*|hell[^o].*|hello..*)$ There has been discussion on comp.compilers recently on calculating the difference between two regular expressions.
From: Janis Papanagnou on 24 Jan 2010 17:42 Icarus Sparry wrote: > On Sun, 24 Jan 2010 14:23:59 +0100, Janis Papanagnou wrote: > >> Stephane CHAZELAS wrote: >>> 2010-01-24, 06:11(+01), Janis Papanagnou: >>>> Seebs wrote: >>>>> I'm not sure that even ksh can do everything posix REs can. >>>> I am confident and quite sure it does. Vice versa; I think the regexp >>>> library will at least have problems emulating ksh's !(...) >>>> construct. Ever tried? In general you'll get extremely bulky results >>>> here! But the class of languages (regular expressions) is the same, >>>> anyway.[*] >>>> >>>> [*] N.B. Newer ksh's also support back-references in their >>>> expressions, so strictly speeking, with that feature, they exceed the >>>> Chomsky-3 grammar class as well (analogous to other libraries with >>>> backreference extensions). >>> [...] >>> >>> Recent versions of AT&T ksh can also convert globbing patterns to >>> regular expressions (a AT&T variant thereof): >>> >>> $ ksh -c 'printf "%R\n" "!(...)"' >>> ^(\.\.\.)!$ >> I didn't knew that ! were a regular expression meta operator in regexp. >> >> The ! _regexp_ meta operator does not seem to produce results on my box. >> >> $ ls >> hello hello world helloworld regexp world $ ls !(hello) >> hello world helloworld regexp world $ ksh -c 'printf "%R\n" >> "!(hello)"' >> ^(hello)!$ >> $ ls | egrep '^(hello)!$' >> ### nothing matched ### >> >> It works well with the known operators + and * etc. resp. +(...) *(...) >> etc. >> >> Still interested in an regexp expression conforming to !(...) ext. glob. > > The grep from AST will handle this '^(hello)!$' if you give it a -X flag > to enable the augmented expressions. Interesting to know. Thanks! This is unique to the AST grep, I suppose. > An instant thought on matching !(hello) with a RE, this is > > ^([^h].*|h[^e].*|he[^l].*|hel[^l].*|hell[^o].*|hello..*)$ Yes, something like that was what I had in mind when I spoke of "extremely bulky results". > There has been discussion on comp.compilers recently on calculating the > difference between two regular expressions. (Must have a look to understand what's meant with differences between REs.) Janis
From: pk on 24 Jan 2010 17:51 Janis Papanagnou wrote: > Still interested in an regexp expression conforming to !(...) ext. glob. Well if lookaround assertions are available, it's trivially done with something like (?!whatyoudontwant).*.ext or equivalent. (Yes, we're way out of the "regular" regexp domain here, probably even more than with backreferences) However, I don't think any shell implements that.
From: Kaz Kylheku on 24 Jan 2010 21:41
On 2010-01-24, Icarus Sparry <usenet(a)icarus.freeuk.com> wrote: > On Sun, 24 Jan 2010 14:23:59 +0100, Janis Papanagnou wrote: > >> Stephane CHAZELAS wrote: >>> 2010-01-24, 06:11(+01), Janis Papanagnou: >>>> Seebs wrote: >>>>> I'm not sure that even ksh can do everything posix REs can. >>>> I am confident and quite sure it does. Vice versa; I think the regexp >>>> library will at least have problems emulating ksh's !(...) >>>> construct. Ever tried? In general you'll get extremely bulky results >>>> here! But the class of languages (regular expressions) is the same, >>>> anyway.[*] >>>> >>>> [*] N.B. Newer ksh's also support back-references in their >>>> expressions, so strictly speeking, with that feature, they exceed the >>>> Chomsky-3 grammar class as well (analogous to other libraries with >>>> backreference extensions). >>> [...] >>> >>> Recent versions of AT&T ksh can also convert globbing patterns to >>> regular expressions (a AT&T variant thereof): >>> >>> $ ksh -c 'printf "%R\n" "!(...)"' >>> ^(\.\.\.)!$ >> >> I didn't knew that ! were a regular expression meta operator in regexp. >> >> The ! _regexp_ meta operator does not seem to produce results on my box. >> >> $ ls >> hello hello world helloworld regexp world $ ls !(hello) >> hello world helloworld regexp world $ ksh -c 'printf "%R\n" >> "!(hello)"' >> ^(hello)!$ >> $ ls | egrep '^(hello)!$' >> ### nothing matched ### >> >> It works well with the known operators + and * etc. resp. +(...) *(...) >> etc. >> >> Still interested in an regexp expression conforming to !(...) ext. glob. > > The grep from AST will handle this '^(hello)!$' if you give it a -X flag > to enable the augmented expressions. > > An instant thought on matching !(hello) with a RE, this is > > ^([^h].*|h[^e].*|he[^l].*|hel[^l].*|hell[^o].*|hello..*)$ Good start. A regular expression denotes a set. The expression "hello" denotes the set { "hello" }. The complement of the regular expression is the complement of this set: it is the (infinite) set of all strings except "hello". This set includes: - the empty string; - all strings of length 1 through length 4; - all strings of length 5 except "hello"; and - all strings of length 6 and greater By articulating the complement result as the above set, we can now write the expression as a union of the constituent categories: (|.|..|...|....|[^h]....|h[^e]...|he[^l]..|hel[^l].|hell[^o]|.......*) I recently implemented an alternative regexp engine in Txr which supports intersection and complement. I wrote up a bit of a regex discussion section in the man page: http://www.nongnu.org/txr/txr-manpage.html |