check if a certain revision (or tag) exists in SVN/subversion

I'm building a phing deployment script where I first ask the u开发者_StackOverflowser to enter the revision/tag to deploy from svn.

when a user enters e.g. 0.1, I would like to check (with a linux script or from svn itself) IF this 0.1 revision actually exists. If it doesn't exist, I want to print an error and stop.

You can use the SVN info command to get information about a folder, file, trunk, branch, tag.