使用 bash 命令(带管道)的输出作为另一个命令的参数 [英] Use output of bash command (with pipe) as a parameter for another command

问题描述

我正在寻找一种方法来使用命令(比如 command1)的输出作为另一个命令(比如 command2)的参数.

I'm looking for a way to use the ouput of a command (say command1) as an argument for another command (say command2).

我在尝试 grep who 命令的输出但使用另一组命令(实际上是 tty)给出的模式时遇到了这个问题通过管道传输到 sed).

I encountered this problem when trying to grep the output of who command but using a pattern given by another set of command (actually tty piped to sed).

如果 tty 显示:

/dev/pts/5

和who显示:

root     pts/4        2012-01-15 16:01 (xxxx)
root     pts/5        2012-02-25 10:02 (yyyy)
root     pts/2        2012-03-09 12:03 (zzzz)

目标:

我只想要有关pts/5"的行所以我通过管道将 tty 传送到 sed 如下:

$ tty | sed 's//dev///'
pts/5

测试:

尝试的以下命令不起作用:

Test:

The attempted following command doesn't work:

$ who | grep $(echo $(tty) | sed 's//dev///')"

可能的解决方案:

我发现以下方法可以正常工作:

Possible solution:

I've found out that the following works just fine:

$ eval "who | grep $(echo $(tty) | sed 's//dev///')"

但我确信可以避免使用 eval.

作为最后一个边节点:我注意到 who 的-m"参数给了我我想要的东西(只得到 whocode> 链接到当前用户).但是我仍然很好奇如何使管道和命令嵌套的这种组合起作用......

As a final side node: I've noticed that the "-m" argument to who gives me exactly what I want (get only the line of who that is linked to current user). But I'm still curious on how I could make this combination of pipes and command nesting to work...

推荐答案

在 Bash 变量修改，尽管@ruakh 指出这在单行版本中不起作用(没有分号分隔命令).我将保留第一种方法，因为我认为它不能在一行中工作很有趣:

You can do this without resorting to sed with the help of Bash variable mangling, although as @ruakh points out this won't work in the single line version (without the semicolon separating the commands). I'm leaving this first approach up because I think it's interesting that it doesn't work in a single line:

TTY=$(tty); who | grep "${TTY#/dev/}"

这首先将 tty 的输出放入一个变量中，然后在 grep 使用它时擦除前导 /dev/.但是没有分号 TTY 在 bash 为 grep 进行变量扩展/修改时不在环境中.

This first puts the output of tty into a variable, then erases the leading /dev/ on grep's use of it. But without the semicolon TTY is not in the environment by the moment bash does the variable expansion/mangling for grep.

这是一个有效的版本，因为它生成了一个具有已修改环境(具有 TTY)的子 shell:

Here's a version that does work because it spawns a subshell with the already modified environment (that has TTY):

TTY=$(tty) WHOLINE=$(who | grep "${TTY#/dev/}")

结果留在$WHOLINE中.

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