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From: Tom Harrington on 21 Jan 2010 17:16
In article <-bmdndcRgr-txsXWnZ2dnUVZ7tSdnZ2d(a)pipex.net>,
TF <awax46(a)dsl.pipex.com> wrote:

> On Thu Jan 21 2010 at 10:30:39 UTC, JF Mezei <jfmezei.spamnot(a)vaxination.ca>
> wrote:
> > Sorry for the newbie question:
> >
> > what is the grep syntax to look for the string "velo" but NOT
> > "development" ?
>
> You can do that "properly" with regular expressions but, at least in
> simple cases, I find myself piping multiple instances of grep instead,
> e.g.
>
> cat file.txt | grep "velo" | grep -v "development"
>
> Here, "-v" makes grep perform what's called an "inverted matching", that
> is, it passes everything through that does NOT match "development".

If you mean "velo" as a word on its own, you can use:

grep '\<velo\>' file.txt

That'll find "velo" with a word boundary on either side. If that's not
what you want then I'd just use TF's approach.

--
Tom "Tom" Harrington
Independent Mac OS X developer since 2002
http://www.atomicbird.com/
From: David Empson on 21 Jan 2010 18:18
Tom Harrington <tph(a)pcisys.no.spam.dammit.net> wrote:

> In article <-bmdndcRgr-txsXWnZ2dnUVZ7tSdnZ2d(a)pipex.net>,
> TF <awax46(a)dsl.pipex.com> wrote:
>
> > On Thu Jan 21 2010 at 10:30:39 UTC, JF Mezei <jfmezei.spamnot(a)vaxination.ca>
> > wrote:
> > > Sorry for the newbie question:
> > >
> > > what is the grep syntax to look for the string "velo" but NOT
> > > "development" ?
> >
> > You can do that "properly" with regular expressions but, at least in
> > simple cases, I find myself piping multiple instances of grep instead,
> > e.g.
> >
> > cat file.txt | grep "velo" | grep -v "development"
> >
> > Here, "-v" makes grep perform what's called an "inverted matching", that
> > is, it passes everything through that does NOT match "development".
>
> If you mean "velo" as a word on its own, you can use:
>
> grep '\<velo\>' file.txt
>
> That'll find "velo" with a word boundary on either side. If that's not
> what you want then I'd just use TF's approach.

That's one I didn't know about, so thanks for the pointer. On further
research it seems to be specific to grep and not to other regular
expressions (e.g. Perl doesn't know it).

A similar regular expression which is compatible with GNU grep and Perl
is:

grep '\bvelo\b' file.txt

The '\b' matches a zero-length word boundary without caring if it is at
the beginning or end of a word.

--
David Empson
dempson(a)actrix.gen.nz
From: Barry Margolin on 21 Jan 2010 18:56
In article <1jcpydn.1lefot27nxzewN%dempson(a)actrix.gen.nz>,
dempson(a)actrix.gen.nz (David Empson) wrote:

> Tom Harrington <tph(a)pcisys.no.spam.dammit.net> wrote:
>
> > In article <-bmdndcRgr-txsXWnZ2dnUVZ7tSdnZ2d(a)pipex.net>,
> > TF <awax46(a)dsl.pipex.com> wrote:
> >
> > > On Thu Jan 21 2010 at 10:30:39 UTC, JF Mezei
> > > <jfmezei.spamnot(a)vaxination.ca>
> > > wrote:
> > > > Sorry for the newbie question:
> > > >
> > > > what is the grep syntax to look for the string "velo" but NOT
> > > > "development" ?
> > >
> > > You can do that "properly" with regular expressions but, at least in
> > > simple cases, I find myself piping multiple instances of grep instead,
> > > e.g.
> > >
> > > cat file.txt | grep "velo" | grep -v "development"
> > >
> > > Here, "-v" makes grep perform what's called an "inverted matching", that
> > > is, it passes everything through that does NOT match "development".
> >
> > If you mean "velo" as a word on its own, you can use:
> >
> > grep '\<velo\>' file.txt
> >
> > That'll find "velo" with a word boundary on either side. If that's not
> > what you want then I'd just use TF's approach.
>
> That's one I didn't know about, so thanks for the pointer. On further
> research it seems to be specific to grep and not to other regular
> expressions (e.g. Perl doesn't know it).

Yes it does, but it uses < and > rather than \< and \>. Perl only uses
backslash before letters in its regular expressions, punctuation
characters that have special meanings are never backslashed.

--
Barry Margolin, barmar(a)alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***
From: David Empson on 21 Jan 2010 19:24
Barry Margolin <barmar(a)alum.mit.edu> wrote:

> In article <1jcpydn.1lefot27nxzewN%dempson(a)actrix.gen.nz>,
> dempson(a)actrix.gen.nz (David Empson) wrote:
>
> > Tom Harrington <tph(a)pcisys.no.spam.dammit.net> wrote:
> >
> > > In article <-bmdndcRgr-txsXWnZ2dnUVZ7tSdnZ2d(a)pipex.net>,
> > > TF <awax46(a)dsl.pipex.com> wrote:
> > >
> > > > On Thu Jan 21 2010 at 10:30:39 UTC, JF Mezei
> > > > <jfmezei.spamnot(a)vaxination.ca>
> > > > wrote:
> > > > > Sorry for the newbie question:
> > > > >
> > > > > what is the grep syntax to look for the string "velo" but NOT
> > > > > "development" ?
> > > >
> > > > You can do that "properly" with regular expressions but, at least in
> > > > simple cases, I find myself piping multiple instances of grep instead,
> > > > e.g.
> > > >
> > > > cat file.txt | grep "velo" | grep -v "development"
> > > >
> > > > Here, "-v" makes grep perform what's called an "inverted matching", that
> > > > is, it passes everything through that does NOT match "development".
> > >
> > > If you mean "velo" as a word on its own, you can use:
> > >
> > > grep '\<velo\>' file.txt
> > >
> > > That'll find "velo" with a word boundary on either side. If that's not
> > > what you want then I'd just use TF's approach.
> >
> > That's one I didn't know about, so thanks for the pointer. On further
> > research it seems to be specific to grep and not to other regular
> > expressions (e.g. Perl doesn't know it).
>
> Yes it does, but it uses < and > rather than \< and \>.

Not in the version of Perl I have (5.10.0 on Snow Leopard). It treats <
and > as literal characters, and I can't see any suggestion of those
characters being special in perldoc perlre.

> Perl only uses backslash before letters in its regular expressions,
> punctuation characters that have special meanings are never backslashed.

Agreed.

--
David Empson
dempson(a)actrix.gen.nz
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