在单个命令中将一个命令的输出附加到另一个命令的输出

Question

有没有办法将一个命令的stdout输出附加到另一个命令并将组合输出传递给另一个命令？我曾经使用以下方法(ack-grep以此为例)

# List all python, js files in different directories
ack-grep -f --py apps/ > temp
ack-grep -f --js -f media/js >> temp
cat temp | xargs somecommand

有没有办法在一个命令中执行此操作？

Answer 1

只需将两个ack-grep命令作为复合命令运行; 然后管道compund命令的结果.定义的第一个复合命令man bash是括号:

   (list) list is executed in a subshell environment (see  COMMAND  EXECU-
              TION  ENVIRONMENT below).  Variable assignments and builtin com-
              mands that affect the  shell's  environment  do  not  remain  in
              effect  after  the  command completes.  The return status is the
              exit status of list.

所以:

james@bodacious-wired:tmp$echo one > one.txt
james@bodacious-wired:tmp$echo two > two.txt
james@bodacious-wired:tmp$(cat one.txt; cat two.txt) | xargs echo
one two

你可以使用花括号来达到类似的效果,但花括号有一些语法差异(例如,它们在括号和其他单词之间需要空格时更加挑剔).最大的区别是大括号内的命令在当前的 shell环境中运行,因此它们会影响您的环境.例如:

james@bodacious-wired:tmp$HELLO=world; (HELLO=MyFriend); echo $HELLO
world
james@bodacious-wired:tmp$HELLO=world; { HELLO=MyFriend; }; echo $HELLO
MyFriend

如果你想真正想要你可以定义一个函数并执行它:

james@bodacious-wired:tmp$myfunc () (
> cat one.txt
> cat two.txt
> )
james@bodacious-wired:tmp$myfunc | xargs echo
one two
james@bodacious-wired:tmp$