Simple Reg. Ex. question regarding * vx +

[DJR999]

Simple Regular Expression Question

OK - I'm new to UNIX and reg. ex, so this is probably very basic, but I can't figure it out. Given a simple text file called namelist with a list of names such as

John Doe
Bob Cat
Billy Bob
Joe Mama

etc,

the command:

grep '[A-Z][a-z]*' namelist

yields all lines, as it should, an upper case letter followed by 0 or more lower case letters.

yet

grep '[A-Z][a-z]+' namelist

yields nothing. Every line starts with one upper case letter followed by one or more lower case, but this yields nothing.

Also

grep '[A-Z][a-z]\{1,\}' namelist

yields every name on the list. I've found a couple of references that say this is identical to the 2nd grep command above (one ore more lower case letters), yet this lists the names, as I would expect, but the [a-z]+ syntax does not.

Can someone explain this to me?

Thank You,

Doug

 

[feherke]

Hi

Both [tt]+[/tt] and [tt]{}[/tt] has to be escaped in basic regular expressions. Or use extended or Perl-like regular expressions.

grep '[A-Z][a-z]\+' namelist
grep -E '[A-Z][a-z]+' namelist
grep -P '[A-Z][a-z]+' namelist

Tested with GNU [tt]grep[/tt].


Feherke.

http://rootshell.be/~feherke/

 

[DJR999]

Hmm.

Well - I guess it must just be a version thing.

Escaping the + does nothing - your first line above still yields no results.

Adding the extended -E option works - when I used your second line I get all of the names listed.

The -P option is not recognized - tells me illegal option.

I am on HP Unix - not sure of the exact implementation. Here is the welcome stuff I get after logging on:

Thanks for the reply.

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[feherke]

Hi

Yepp, that is why I specified that I tested my suggestions with GNU [tt]grep[/tt]. Honestly, I am surprised that -E worked for you.

Some tools on Unix not handle the [tt]+[/tt] quantifier, so you can see workarounds like this :

grep '[A-Z][a-z][a-z]*' namelist

Feherke.

http://rootshell.be/~feherke/

 

[PHV]

man egrep

Hope This Helps, PH.
FAQ219-2884
FAQ181-2886