tps@chem.ucsd.edu (Tom Stockfisch) (03/14/90)
The following awk script doesn't behave properly:
#! /bin/sh
awk '/^a*[^b]/ { print "1:", $0 }
/^a*b/ { print "2:", $0 }
'
When given the following input
b
ab
It produces the following output
2: b
1: ab
2: ab
Basically, the line "ab" should match only rule 2, but it matches both
rules. The following script:
#! /bin/sh
awk '/^a*[^b]c/ { print "1:", $0 }
/^a*bc/ { print "2:", $0 }
'
works, producing the output
2: bc
2: abc
The corresponding lex program works fine.
I have run the awk script with both the new awk and old awk, on both
a system V machine (silicon graphics iris) and a 4BSD machine (celerity)
and all seem to fail.
--
|| Tom Stockfisch, UCSD Chemistry tps@chem.ucsd.edum5@lynx.uucp (Mike McNally) (03/14/90)
tps@chem.ucsd.edu (Tom Stockfisch) writes: >The following awk script doesn't behave properly: >#! /bin/sh >awk '/^a*[^b]/ { print "1:", $0 } >/^a*b/ { print "2:", $0 } >' >When given the following input >b >ab >It produces the following output >2: b >1: ab >2: ab >Basically, the line "ab" should match only rule 2 . . . I disagree: a*[^b] => <null>[^b] => <null>a The a* is matching the empty string, and the [^b] is matching the a. -- Mike McNally Lynx Real-Time Systems uucp: {voder,athsys}!lynx!m5 phone: 408 370 2233 Where equal mind and contest equal, go.
magnus@rhi.hi.is (Magnus Gislason) (03/15/90)
tps@chem.ucsd.edu (Tom Stockfisch) writes: >The following awk script doesn't behave properly: >#! /bin/sh >awk '/^a*[^b]/ { print "1:", $0 } >/^a*b/ { print "2:", $0 } >' [stuff deleted] >Basically, the line "ab" should match only rule 2, but it matches both >rules. The following script: In Regular Expressions `a*' meens 0 or more occurrencies of `a' and `[^b]' meens any character except `b'. In this case `a*[^b]' matches 0 `a's followed by a character that is not `b' (in this case `a'). I tried this with grep, egrep, sed and vi and they all behaved like awk so I suppose it's the correct way.
merlyn@iwarp.intel.com (Randal Schwartz) (03/15/90)
In article <702@chem.ucsd.EDU>, tps@chem (Tom Stockfisch) writes: | | The following awk script doesn't behave properly: | | #! /bin/sh | | awk '/^a*[^b]/ { print "1:", $0 } | /^a*b/ { print "2:", $0 } | ' | | When given the following input | | b | ab | | It produces the following output | | 2: b | 1: ab | 2: ab | | Basically, the line "ab" should match only rule 2, but it matches both | rules. [This doesn't belong in WIZARDS. Sorry.] But, it *does* match rule 1! Look carefully. If you take zero 'a's, and one 'not b', you can get line "ab"! In Perl: perl -ne 'print "1: $_" if /^a*[^b]/; print "2: $_" if /^a*b/;' <<EOF b ab EOF produces: 2: b 1: ab 2: ab Just like awk. Amazing. No problem. Just another Perl and awk hacker, -- /=Randal L. Schwartz, Stonehenge Consulting Services (503)777-0095 ==========\ | on contract to Intel's iWarp project, Beaverton, Oregon, USA, Sol III | | merlyn@iwarp.intel.com ...!any-MX-mailer-like-uunet!iwarp.intel.com!merlyn | \=Cute Quote: "Welcome to Portland, Oregon, home of the California Raisins!"=/