nameis=${dataset%.*}

…例如：

$ dataset=foo.txt
$ nameis=${dataset%.*}
$ echo $nameis
foo

这种语法在bash手册页中描述为：

${parameter%word}

${parameter%%word}

Remove matching suffix pattern. The word is expanded to produce a pattern just as in pathname expansion. If the pattern matches a trailing portion of the expanded value of parameter,then the result of the expansion is the expanded value of parameter with the shortest matching pattern (the “%” case) or the longest matching pattern (the “%%” case) deleted. If parameter is @ or *,the pattern removal operation is applied to each positional parameter in turn,and the expansion is the resultant list. If parameter is an array variable subscripted with @ or *,the pattern removal operation is applied to each member of the array in turn,and the expansion is the resultant list.