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grep and alphanumerics

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# 1  
Old 10-26-2012
grep and alphanumerics
Hi Experts,

I'm facing an issue with grep or may be Im missing something. Following are the details

Code:
Input file

[root@#### ~]# more regexp
asdh1987

dog897you
981towm

1234oqn
4yuop8pou
sam99917c00l
Akoold0g8
data
sample data

Im trying to grep out only the alphanumeric entries and following is the output
Code:
[root@#### ~]# grep -Ei '[:alnum:]' regexp
asdh1987
dog897you
981towm
1234oqn
4yuop8pou
sam99917c00l
Akoold0g8
data
sample data

However when i do the same thing using the following command it works

Code:
[root@### ~]# grep -Ei '[a-z][0-9]|[0-9][a-z]' regexp
asdh1987
dog897you
981towm
1234oqn
4yuop8pou
sam99917c00l
Akoold0g8

Am i missing something, please advise
# 2  
Old 10-26-2012
The RE you used ([:alnum:]) matched lines that contained an 'a', 'l', 'n', 'u', 'm', or ':'. To specify an RE with a bracket expression matching any character in the alnum character class, you need to use [[:alnum:]].
# 3  
Old 10-26-2012
Not working
I have used the following command

Code:
[root@nagois ~]# grep '[[:alnum:]]' regexp
asdh1987
dog897you
981towm
1234oqn
4yuop8pou
sam99917c00l
Akoold0g8
data
sample data

It is dumping all the entries excluding blank lines but not alpha numeric entries
# 4  
Old 10-26-2012
Alphanumeric means lowercase, uppercase or numeric...
# 5  
Old 10-26-2012
Very true
however the grep is pulling up

Code:
data
sample data

which are only lower case
# 6  
Old 10-26-2012
The bracket expression [[:alnum:]] will match one of the characters A-Z,a-z,0-9; that's a single-character pattern. If your line has at least one of these characters, the pattern will match.
# 7  
Old 10-26-2012
Code:
[:alnum:]  - Any digit or Alphanumeric
[:alpha:]  - Any Alphanumeric

May be this could be the reason. Try using [:alpha:]

Elixir has good point here.Smilie

Please check http://ss64.com/osx/grep_pattern.html
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