<basename property="jar.filename" file="${lib.jarfile}"/>will set jar.filename to myjar.jar, if lib.jarfile is defined as either a full-path filename (eg., /usr/local/lib/myjar.jar), a relative-path filename (eg., lib/myjar.jar), or a simple filename (eg., myjar.jar).
<basename property="cmdname" file="D:/usr/local/foo.exe" suffix=".exe"/>will set cmdname to foo.
<property environment="env"/> <basename property="temp.dirname" file="${env.TEMP}"/>will set temp.dirname to the last directory element of the path defined for the TEMP environment variable.