标准unix util将“foo.bar.baz”拆分为“foo.bar”+“.baz”？

Question 1

您可以仅使用 Bash 中包含的普通字符串解析函数来执行非常接近您想要的操作：

$ F="foo.bar.baz"

$ echo ${F%.*}
foo.bar

$ echo ${F/*./.}
.baz

所以你可以像这样把它放在一起：

$ $ F="foo.bar.baz"

$ stem=${F%.*}
$ ext=${F/*./.}

echo "${stem}${ext}"
foo.bar.baz

摘自 Bash 手册页

${F%.*}

${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.

${/*./.}

${parameter/pattern/string}
   Pattern  substitution.   The pattern is expanded to produce a pattern just
   as in pathname expansion.  Parameter is expanded and the longest match of 
   pattern against its value is replaced with string.  If pattern  begins 
   with  /, all  matches  of  pattern are replaced with string.  Normally
   only the first match is replaced.  If pattern begins with #, it must match
   at the beginning of the expanded value of parameter.  If pattern  begins
   with  %,  it  must match  at the end of the expanded value of parameter.
   If string is null, matches of pattern are deleted and the / following
   pattern may be omitted.  If parameter is @ or *, the substitution 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 substitution operation is applied to each member of the
   array in turn, and the expansion  is  the resultant list.

您可以在以下位置阅读有关这些功能的信息Bash 手册页。

Answer

您可以仅使用 Bash 中包含的普通字符串解析函数来执行非常接近您想要的操作：

$ F="foo.bar.baz"

$ echo ${F%.*}
foo.bar

$ echo ${F/*./.}
.baz

所以你可以像这样把它放在一起：

$ $ F="foo.bar.baz"

$ stem=${F%.*}
$ ext=${F/*./.}

echo "${stem}${ext}"
foo.bar.baz

摘自 Bash 手册页

${F%.*}

${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.

${/*./.}

${parameter/pattern/string}
   Pattern  substitution.   The pattern is expanded to produce a pattern just
   as in pathname expansion.  Parameter is expanded and the longest match of 
   pattern against its value is replaced with string.  If pattern  begins 
   with  /, all  matches  of  pattern are replaced with string.  Normally
   only the first match is replaced.  If pattern begins with #, it must match
   at the beginning of the expanded value of parameter.  If pattern  begins
   with  %,  it  must match  at the end of the expanded value of parameter.
   If string is null, matches of pattern are deleted and the / following
   pattern may be omitted.  If parameter is @ or *, the substitution 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 substitution operation is applied to each member of the
   array in turn, and the expansion  is  the resultant list.

您可以在以下位置阅读有关这些功能的信息Bash 手册页。

Question 2

不能有命令设置 shell 的变量，因为变量是 shell 进程内部的东西，所以另一个命令，生活在它自己的进程中，不可能改变它。

使用 shell，您可以执行以下操作：

var=$(some-command)

检索命令的输出（不带尾随换行符），但如果您需要命令的两个结果，那就会变得更加棘手。

一种方法如下：

eval "$(some-command)"

其中 some-command 输出如下内容：

var1='something' var2='someotherthing'

但在你问之前，没有这样的标准命令可以采用路径并将其拆分为目录、基本名称和扩展名（无论这意味着什么）。

现在，外壳本身可能具有用于此目的的内部功能。例如csh，zsh有可以给你头部、尾部、延伸的修饰符。像zsh：

file=/path/to/foo.bar/
head=$file:h
tail=$file:t
ext=$file:e
rest=$file:r

.现在您可能需要考虑对于像or ..、/、.bashrcor foo.tar.gz?这样的文件来说，这些应该是什么？

现在，如果您正在寻找标准 POSIX 语法，那么您已经（几乎）拥有它了：rest=${file%.*}。${file#$rest}是zsh具体的。在 POSIX 语法中，您需要ext=${file#"$rest"}, 否则$rest被视为模式。请注意，如果$file包含带有字符的路径/（例如foo.d/bar），可能不会执行您想要的操作。

Answer