$ {REV %% $'\ n *'} 似乎有效.参见 bash文档的引用部分.>

does not work

echo ${REV%%\n*}

does work

echo ${REV%%
*}

After reading trough http://tldp.org/LDP/abs/html/parameter-substitution.html I still can not figure out how to make \n work.

${REV%%$'\n*'} seems to work. See the quoting section of the bash documentation.