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 "$string" '[0-9][.][0-9]'`
}
However, this doesn't match the 3.4 in the string. Can anyone point me in the right direction here?
Thanks.
First, you can drop the echo - expr prints its result to stdout in any case.
Second, your regex needs brackets (otherwise it prints the number of characters matched, not the match itself), and it needs to begin with .*.
expr match "$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.
Depending on your version of bash, there's no need to call out to expr:
$ [[ "abc ABC12 123 3.4 def" =~ [0-9][.][0-9] ]] && echo ${BASH_REMATCH[0]}
3.4
Thinking outside the box: if what you are looking for is determining the OS version in a script, just use uname -r or uname -v (it's POSIX). Messing with regular expression is likely to have issues as each OS may have different ways to express its version. OS vendors are so creative in inventing version jumps forward and backward, some have letters in there, and even roman numerals are not unheard of (think System V).
See http://pubs.opengroup.org/onlinepubs/9699919799/utilities/uname.html
I use in my .profile a snippet like this:
case "`uname -sr`" in
(*BSD*) OS=`uname -s`;;
(SunOS\ 4*) OS=SunOS;;
(SunOS\ 5*) OS=Solaris;;
(IRIX\ 5*) OS=IRIX;;
(HP*) OS=HP-UX;;
(Linux*) OS=Linux;;
(CYGWIN*) OS=Cygwin;;
(*) OS=generic
esac
On Mac OS X 10.6.8:
# cf. http://tldp.org/LDP/abs/html/refcards.html#AEN22429
string="abc ABC12 123 3.4 def"
expr "$string" : '.*\([0-9].[0-9]\)' # 3.4
expr match "$string" '.*[0-9][.][0-9]'
[0-9]\.[0-9][.]any single character? Does your function match anything at all? I don't know the specifics of regex in bash, but I would assume the match would be something like "2 1".expr match STRING REGEXreturns 0 if there's a match, nonzero otherwise. This is what happens with your example on my machine.