Shell Programming and Scripting

Need help with the following, I want to extract the digits from the following file pattern
using the expr command. digits are in the range 1-99

Tried two different methods, not sure what I am doing wrong.

file1=file1.dbf
file10=file10.dbf

Works for

expr "$file10" : '.*\([0-9][0-9]\)'
10

But not for

expr "$file1" : '.*\([0-9][0-9]\)'
<blank>

Tried to use the repitition operator but once again did not work as expected.
Incorrectly extracts the second digit only.

expr "$file10" : '.*\([0-9]\{1,2\}\)'
0

Repetition operator accepts the minimum value.
This was confirmed with the following ...

expr "$file10" : '.*\([0-9]\{2\}\)'
10

You dont really need expr for that..you can use sed or tr. Are you specifically looking for a expr command?

Thanks Devtakh,
echo "$file10" | tr -cd '[[:digit:]]' worked...
Will use this method instead. However if anyone
could explain what I did wrong with expr I would
appreciate it.

Thanks