473,378 Members | 1,536 Online
Bytes | Software Development & Data Engineering Community
Post Job

Home Posts Topics Members FAQ

Join Bytes to post your question to a community of 473,378 software developers and data experts.

Regular Expression help

Hello,

Please forgive if this is not the most appropriate newsgroup for this
question. Unfortunately I didn't find a newsgroup specific to regular
expressions.

I have the following regular expression.

^(.+?) uses (?!a spoon)\.$

I know something is wrong with this, but essentially what I want to do
is match all strings of the form

^(.+?) uses (.+?)\.$

but only if the text inside that last group is not the string "a
spoon".

When this is tested against the string

Jim uses a fork.

the test fails. It says "Jim uses a fork." does not match the regular
expression "^(.+?) uses (?!a spoon)\.$"

Am I missing something obvious here?

Thanks for any help.

May 27 '06 #1
3 2534
Zach wrote:
When this is tested against the string

Jim uses a fork.

the test fails. It says "Jim uses a fork." does not match the regular
expression "^(.+?) uses (?!a spoon)\.$"

Am I missing something obvious here?


In your pattern you kind of say to "not match 'a spoon'", but you didn't
tell it to match "anything else instead of it", thats why "Jim uses a
fork." fails.

I think this should work:

string pattern = @"^(.+?) uses (?!a spoon).*?\.$";

That says "dont match 'uses a spoon', but match 'uses anything else'".

hth,
Max
May 28 '06 #2
Ahh, thanks. After reading your response I played around with it a
little more. I guess now I know why they're called "zero-width"
assertions. I guess I had thought that saying (?!a spoon)\. would
consume everything from the current location to the next period
character, but only if that was not equal to "a spoon". But it appears
to only verify that the string does not follow, without moving the
current position forward (hence the zero-width). The expression you
suggested works, thanks.

May 28 '06 #3
Okay, you're playing a little fast and loose with your rules, but based upon
my best guess as to what your rules are, let me start with my best guess as
to what the rules are:

First, you state that you want to match "all strings of the form..." This
does not make it clear whether these "strings" have multiple lines in them.
But based upon your syntax, which employs the '^' (Start of string) and '$'
(end of string) characters, I'm going to assume that perhaps you will be
working with multi-lined text (otherwise, at least one of the start of
string and end of string characters would be irrelevant). Based upon that
assumption, my derived rule begins thus:

A match begins at the start of a line, and ends at the end of a line (not
only at the start and end of a string)

Next, your regular expression indicates that any non-line-break character is
a match, *as long as* it is followed by [the string "uses " *not* followed
by the string "a spoon" *but is* followed by some other characters], and
ending with a period.

This breaks down into the following rule set:

1. A match begins at the beginning of a line.
2. It begins with at least one non-line-break character.
3. That sequence of character or characters *must* be followed by the
literal "uses ".
4. The literal "uses " *must not* be followed by the literal "a spoon".
5. The literal "uses " *must* be followed by at least one non-line-break
character.
6. The total sequence *must* end with a period.
7. The period *must* be at the end of a line.

Note that if any of these conditions fail, the entire match fails.

The evaluates to the following regular expression:

(?m)^.+(?=uses (?!a spoon)).+\.$

The first part ("(?m)") indicates that the characters '^' and '$' match at
line breaks, rather then at the beginning and end of a string. You may want
to change this if you're only evaluating a single string, rather than a
series of lines in a single string.

This is followed by '^' (must begin at the beginning of a line or string).

This is followed by '.' with the quantifier '+' (one or more of any
non-line-break character)

This is followed by a positive look-ahead, which states that this must be
followed by the literal "uses ". In addition, the literal "uses " is
followed by a negative look-ahead which prohibits the match if "uses " is
followed by the literal "a spoon". Both conditions must be true in order to
match the first part of the regular expression (must be followed by "uses "
*not* followed by "a spoon").

This is followed by '.' with the quantifier '+' (one or more of any
non-line-break character), meaning that the word "uses " must be followed by
one or more non-line-break characters.

This is followed by "\." (a period, one time), followed by a line break or
end of string.

I tested it with the following (the ones with numbers matched):

blah hoiuyy uses ouhsd7)) u. [1]
d;fj uses a fork uses spoon. [2]
lkjhlkjh uses a spoon.
usese a soon or a fork and is the glliiig.
spen duh a spoon
he uses a spoon.
he uses a fork. [3]
popiu hig spoon uses something. [4]
She uses.
uses a fork.
use a spoon.
He uses a spoon, but also uses a fork. [5]
She uses a spoon, not a fork.
He uses forks, knives, and a spoon. [6]
He uses a fork
or a spoon.

These matched because "uses " is not the first word in the line, is followed
by a sequence of characters that is not "a spoon", and the line ends with a
period.

Some other notable results:

"She uses." The word "uses" is not followed by any characters before the
period.
"uses a fork." The word "uses" is the first word on the line (not preceded
by any characters).
Number 5 succeeds because of the phrase "uses a fork". The phrase "uses a
spoon" is considered as part of the first sequence of "any non-line-break
character". Since this is followed by "uses a fork", that phrase causes the
whole to match.
The last 2 lines do not match because of the line break.

--
HTH,

Kevin Spencer
Microsoft MVP
Professional Numbskull

This is, by definition, not that.

"Zach" <di***********@gmail.com> wrote in message
news:11**********************@38g2000cwa.googlegro ups.com...
Hello,

Please forgive if this is not the most appropriate newsgroup for this
question. Unfortunately I didn't find a newsgroup specific to regular
expressions.

I have the following regular expression.

^(.+?) uses (?!a spoon)\.$

I know something is wrong with this, but essentially what I want to do
is match all strings of the form

^(.+?) uses (.+?)\.$

but only if the text inside that last group is not the string "a
spoon".

When this is tested against the string

Jim uses a fork.

the test fails. It says "Jim uses a fork." does not match the regular
expression "^(.+?) uses (?!a spoon)\.$"

Am I missing something obvious here?

Thanks for any help.

May 28 '06 #4

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

5
by: Bradley Plett | last post by:
I'm hopeless at regular expressions (I just don't use them often enough to gain/maintain knowledge), but I need one now and am looking for help. I need to parse through a document to find a URL,...
4
by: Neri | last post by:
Some document processing program I write has to deal with documents that have headers and footers that are unnecessary for the main processing part. Therefore, I'm using a regular expression to go...
10
by: Lee Kuhn | last post by:
I am trying the create a regular expression that will essentially match characters in the middle of a fixed-length string. The string may be any characters, but will always be the same length. In...
3
by: James D. Marshall | last post by:
The issue at hand, I believe is my comprehension of using regular expression, specially to assist in replacing the expression with other text. using regular expression (\s*) my understanding is...
7
by: Billa | last post by:
Hi, I am replaceing a big string using different regular expressions (see some example at the end of the message). The problem is whenever I apply a "replace" it makes a new copy of string and I...
9
by: Pete Davis | last post by:
I'm using regular expressions to extract some data and some links from some web pages. I download the page and then I want to get a list of certain links. For building regular expressions, I use...
25
by: Mike | last post by:
I have a regular expression (^(.+)(?=\s*).*\1 ) that results in matches. I would like to get what the actual regular expression is. In other words, when I apply ^(.+)(?=\s*).*\1 to " HEART...
3
by: Mr.Steskal | last post by:
Posted: Wed Jul 11, 2007 7:01 am Post subject: Regular Expression Help -------------------------------------------------------------------------------- I need help writing a regular...
18
by: Lit | last post by:
Hi, I am looking for a Regular expression for a password for my RegExp ValidationControl Requirements are, At least 8 characters long. At least one digit At least one upper case character
0
by: Faith0G | last post by:
I am starting a new it consulting business and it's been a while since I setup a new website. Is wordpress still the best web based software for hosting a 5 page website? The webpages will be...
0
isladogs
by: isladogs | last post by:
The next Access Europe User Group meeting will be on Wednesday 3 Apr 2024 starting at 18:00 UK time (6PM UTC+1) and finishing by 19:30 (7.30PM). In this session, we are pleased to welcome former...
0
by: ryjfgjl | last post by:
In our work, we often need to import Excel data into databases (such as MySQL, SQL Server, Oracle) for data analysis and processing. Usually, we use database tools like Navicat or the Excel import...
0
by: taylorcarr | last post by:
A Canon printer is a smart device known for being advanced, efficient, and reliable. It is designed for home, office, and hybrid workspace use and can also be used for a variety of purposes. However,...
0
by: Charles Arthur | last post by:
How do i turn on java script on a villaon, callus and itel keypad mobile phone
0
by: ryjfgjl | last post by:
If we have dozens or hundreds of excel to import into the database, if we use the excel import function provided by database editors such as navicat, it will be extremely tedious and time-consuming...
0
by: ryjfgjl | last post by:
In our work, we often receive Excel tables with data in the same format. If we want to analyze these data, it can be difficult to analyze them because the data is spread across multiple Excel files...
0
by: emmanuelkatto | last post by:
Hi All, I am Emmanuel katto from Uganda. I want to ask what challenges you've faced while migrating a website to cloud. Please let me know. Thanks! Emmanuel
1
by: nemocccc | last post by:
hello, everyone, I want to develop a software for my android phone for daily needs, any suggestions?

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.