Unix通配符扩展/正则表达式

Question

What will the below command do?

ls -l ${INPUT%.jnl}.jnl

$INPUT consists of some value.

Answer 1

${INPUT%.jnl} strips the shortest match of .jnl from the back of $INPUT .

By then saying ${INPUT%.jnl}.jnl it looks like a way to make $INPUT consist in something + .jnl and prevent it being two times .jnl at the end, if $INPUT already contained that value.

So ls -l ${INPUT%.jnl}.jnl will perform a ls -l in the path/name indicated by $INPUT , making sure it ends with .jnl .

See some tests regarding the ${INPUT%.jnl} expression:

$ var="hello.jnl.jnlbye"
$ echo ${var%.jnl}
hello.jnl.jnlbye    # as .jnl is not present in the back, nothing gets removed

$ var="hello.jnl.jnl"
$ echo ${var%.jnl}
hello.jnl           # it removed the last .jnl