Linux 使用 Bash 按列拆分命令的输出？
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Split output of command by columns using Bash?
提问by flybywire
I want to do this:
我想做这个：
- run a command
- capture the output
- select a line
- select a column of that line
- 运行命令
- 捕获输出
- 选择一行
- 选择该行的一列
Just as an example, let's say I want to get the command name from a $PID(please note this is just an example, I'm not suggesting this is the easiest way to get a command name from a process id - my real problem is with another command whose output format I can't control).
举个例子，假设我想从 a 获取命令名称$PID（请注意这只是一个例子，我并不是说这是从进程 ID 获取命令名称的最简单方法 - 我真正的问题是另一个我无法控制其输出格式的命令）。
If I run psI get:
如果我跑ps我得到：
PID TTY TIME CMD
11383 pts/1 00:00:00 bash
11771 pts/1 00:00:00 ps
Now I do ps | egrep 11383and get
现在我做的ps | egrep 11383，并得到
11383 pts/1 00:00:00 bashNext step: ps | egrep 11383 | cut -d" " -f 4. Output is:
下一步：ps | egrep 11383 | cut -d" " -f 4。输出是：
<absolutely nothing/>
The problem is that cutcuts the output by single spaces, and as psadds some spaces between the 2nd and 3rd columns to keep some resemblance of a table, cutpicks an empty string. Of course, I could use cutto select the 7th and not the 4th field, but how can I know, specially when the output is variable and unknown on beforehand.
问题是cut通过单个空格切割输出，并ps在第 2 列和第 3 列之间添加一些空格以保持表格的一些相似性，cut选择一个空字符串。当然，我可以cut用来选择第 7 个而不是第 4 个字段，但是我怎么知道，特别是当输出是可变的并且事先未知时。
采纳答案by unwind
回答by soulmerge
Getting the correct line (example for line no. 6) is done with head and tail and the correct word (word no. 4) can be captured with awk:
使用 head 和 tail 获取正确的行（例如第 6 行），并且可以使用 awk 捕获正确的单词（第 4 个单词）：
command|head -n 6|tail -n 1|awk '{print }'
回答by brianegge
I think the simplest way is to use awk. Example:
我认为最简单的方法是使用awk。例子：
$ echo "11383 pts/1 00:00:00 bash" | awk '{ print ; }'
bash
回答by James Anderson
try
尝试
ps |&
while read -p first second third fourth etc ; do
if [[ $first == '11383' ]]
then
echo got: $fourth
fi
done
回答by P Shved
Instead of doing all these greps and stuff, I'd advise you to use ps capabilities of changing output format.
我建议您不要使用所有这些 grep 和东西，而是使用 ps 更改输出格式的功能。
ps -o cmd= -p 12345
You get the cmmand line of a process with the pid specified and nothing else.
您将获得指定 pid 的进程的 cmdand 行，而没有其他任何内容。
This is POSIX-conformant and may be thus considered portable.
这是符合 POSIX 的，因此可以被认为是可移植的。
回答by frayser
Using array variables
使用数组变量
set $(ps | egrep "^11383 "); echo
or
或者
A=( $(ps | egrep "^11383 ") ) ; echo ${A[3]}
回答by Xennex81
Please note that the tr -s ' 'option will not remove any single leading spaces. If your column is right-aligned (as with pspid)...
请注意，该tr -s ' '选项不会删除任何单个前导空格。如果您的列是右对齐的（与pspid 一样）...
$ ps h -o pid,user -C ssh,sshd | tr -s " "
1543 root
19645 root
19731 root
Then cutting will result in a blank line for some of those fields if it is the first column:
如果它是第一列，那么切割将导致其中一些字段的空行：
$ <previous command> | cut -d ' ' -f1
19645
19731
Unless you precede it with a space, obviously
除非你在它前面加一个空格，显然
$ <command> | sed -e "s/.*/ &/" | tr -s " "
Now, for this particular case of pid numbers (not names), there is a function called pgrep:
现在，对于 pid 数字（不是名称）的这种特殊情况，有一个名为 的函数pgrep：
$ pgrep ssh
Shell functions
外壳函数
However, in general it is actually still possible to use shell functionsin a concise manner, because there is a neat thing about the readcommand:
但是，总的来说，实际上仍然可以以简洁的方式使用shell 函数，因为该read命令有一个巧妙的地方：
$ <command> | while read a b; do echo $a; done
The first parameter to read, a, selects the first column, and if there is more, everything elsewill be put in b. As a result, you never need more variables than the number of your column +1.
要读取的第一个参数a，选择第一列，如果还有更多，其他所有内容都会放入b。因此，您永远不需要比列数更多的变量+1。
So,
所以，
while read a b c d; do echo $c; done
will then output the 3rd column. As indicated in my comment...
然后将输出第三列。正如我的评论中指出的那样......
A piped read will be executed in an environment that does not pass variables to the calling script.
管道读取将在不将变量传递给调用脚本的环境中执行。
out=$(ps whatever | { read a b c d; echo $c; })
arr=($(ps whatever | { read a b c d; echo $c $b; }))
echo ${arr[1]} # will output 'b'`
The Array Solution
阵列解决方案
So we then end up with the answer by @frayser which is to use the shell variable IFS which defaults to a space, to split the string into an array. It only works in Bash though. Dash and Ash do not support it. I have had a really hard time splitting a string into components in a Busybox thing. It is easy enough to get a single component (e.g. using awk) and then to repeat that for every parameter you need. But then you end up repeatedly calling awk on the same line, or repeatedly using a read block with echo on the same line. Which is not efficient or pretty. So you end up splitting using ${name%% *}and so on. Makes you yearn for some Python skills because in fact shell scripting is not a lot of fun anymore if half or more of the features you are accustomed to, are gone. But you can assume that even python would not be installed on such a system, and it wasn't ;-).
因此，我们最终得到@frayser 的答案，即使用默认为空格的 shell 变量 IFS 将字符串拆分为数组。不过它只适用于 Bash。Dash 和 Ash 不支持它。在 Busybox 中，我很难将一个字符串拆分为多个组件。获取单个组件（例如使用 awk）然后为您需要的每个参数重复该组件是很容易的。但是你最终会在同一行上反复调用 awk，或者在同一行上反复使用带有 echo 的读取块。这既不高效也不漂亮。所以你最终分裂使用 ${name%% *}等等。让你渴望掌握一些 Python 技能，因为实际上，如果你习惯的一半或更多功能都消失了，shell 脚本编写就不再有趣了。但是你可以假设在这样的系统上甚至不会安装 python，它不是;-)。
回答by fedorqui 'SO stop harming'
Your command
你的命令
ps | egrep 11383 | cut -d" " -f 4
misses a tr -sto squeeze spaces, as unwind explains in his answer.
错过 atr -s来挤压空间，正如 unwind 在他的回答中所解释的那样。
However, you maybe want to use awk, since it handles all of these actions in a single command:
但是，您可能想要使用awk，因为它在单个命令中处理所有这些操作：
ps | awk '/11383/ {print }'
This prints the 4th column in those lines containing 11383. If you want this to match 11383if it appears in the beginning of the line, then you can say ps | awk '/^11383/ {print $4}'.
这将打印包含11383. 如果您希望它匹配11383出现在行首，那么您可以说ps | awk '/^11383/ {print $4}'.
回答by Chris Koknat
Similar to brianegge's awk solution, here is the Perl equivalent:
类似于 brianegge 的 awk 解决方案，这里是 Perl 的等价物：
ps | egrep 11383 | perl -lane 'print $F[3]'
-aenables autosplit mode, which populates the @Farray with the column data.
Use -F,if your data is comma-delimited, rather than space-delimited.
-a启用自动拆分模式，该模式@F使用列数据填充数组。
使用-F,如果你的数据是用逗号分隔的，而不是空格分隔。
Field 3 is printed since Perl starts counting from 0 rather than 1
因为 Perl 从 0 而不是 1 开始计数，所以会打印字段 3
回答by dman
Bash's setwill parse all output into position parameters.
Bashset会将所有输出解析为位置参数。
For instance, with set $(free -h)command, echo $7will show "Mem:"
例如，使用set $(free -h)命令，echo $7将显示“Mem：”
