Question

I’m trying to match a version number from a string in the format 4.6, or 2.8. I have the following which I will eventually use in a function in my .bashrc file to find the OS version:

function test () {
    string="abc ABC12 123 3.4 def";
    echo `expr match "$string" '[0-9][.][0-9]'`
}

However, this doesn’t match the 3.4 in the string. Can anyone point me in the right direction here?

Thanks.

Answer 1

First, you can drop the echo – expr prints its result to stdout in any case.

Second, your regex needs brackets (otherwise it prints the number of characters matched, not the match itself), and it needs to begin with .*.

expr match "$string" '.*\([0-9][.][0-9]\)'

From the info expr page:

STRING : REGEX’

 Perform pattern matching.  The arguments are converted to strings
 and the second is considered to be a (basic, a la GNU `grep')
 regular expression, with a `^' implicitly prepended.  The first
 argument is then matched against this regular expression.

 If the match succeeds and REGEX uses `\(' and `\)', the `:'
 expression returns the part of STRING that matched the
 subexpression; otherwise, it returns the number of characters
 matched.