How do I obtain only digits from a string?

Question

Suppose I have a string like this:

blah=-Xms512m

I want the output as 512 .

I know I can get it using grep on Linux like this: echo $blah | grep -o -e [0-9]\\\\+ echo $blah | grep -o -e [0-9]\\\\+ But this doesn't work on Solaris .

Any nice solutions so that it's compatible on both, Linux and Solaris? Or atleast on Solaris?

Answer 1

I f you know the numbers will be together like that:

pax> echo 'blah=-Xms512m' | sed 's/[^0-9]//g'
512

It basically replaces all non-numeric characters with nothing. Of course, it won't do sensible stuff with:

pax> echo 'blah77=-Xms512m' | sed 's/[^0-9]//g'
77512

but, if you've only got one number it will work fine.

If you just need the first number, you can use:

pax> echo 'blah77=-Xms512m' | sed -e 's/^[^0-9]*//' -e 's/[^0-9].*$//'
77

For the last:

pax> echo 'blah77=-Xms512m' | sed -e 's/[^0-9]*$//' -e 's/^.*[^0-9]//'
512

Answer 2

如果要完全使用蛮力，请尝试使用tr：

echo "blah=-Xms512m" | tr -c -d '[0-9]'