bash命令替换使用变量 [英] Bash Command Substitution with Variables

问题描述

我有一个建立了基于文件的列表中的命令，以便命令是建立在飞bash脚本。构建它的飞行意味着它被保存在一个变量。然后，我要运行该命令，输出存储在一个单独的变量。当我使用命令替换尝试运行命令，它掷骰子了。我怎样才能得到命令替换在一个变量与命令工作时可变利用管？

下面是我的脚本：

 ＃查找因为在365天旧文件数ignored_files =（'文件1'文件2''文件3'）
path_to_examine =/ tmp目录/
newer_than = 365CMD =$找到-mtime path_to_examine  -  $ newer_than
在$ {ignored_files [@]}的文件;做
    CMD =$ CMD | grep的-v \\$文件\\
DONE
CMD =$ CMD |厕所-l
回声运行：$ CMD
num_active_files =`$ cmd`
回声修改少于$ newer_than天前NUM文件：$ num_active_files
 

输出如果我运行该程序：

 ＃./test2.sh
跑步：找的/ tmp / -mtime -365 | grep的-v文件1| grep的-v文件2| grep的-v文件3|厕所-l
发现：坏的选择|
发现：[-H | -L]路径列表predicate名单
＃
 

输出如果我运行CMD：

 ＃NUM =`找到的/ tmp / -mtime -365 | grep的-v文件1| grep的-v文件2| grep的-v文件3| WC -l`
＃$回声NUM
10
＃
 

解决方案

您必须使用评估命令：

  num_active_files =`$ EVAL var`
 

这允许你生成一个前pression对于bash动态运行。

希望这有助于=）

I have a bash script that builds a command based on a list of files so the command is built on the fly. Building it on the fly means it gets stored in a variable. I then want to run that command and store the output in a separate variable. When I use command substitution to try and run the command, it craps out. How can I get command substitution to work with a command in a variable when that variable utilizes pipes?

Here is my script:

# Finds number of files that are over 365 days old

ignored_files=( 'file1' 'file2' 'file3' )
path_to_examine="/tmp/"
newer_than=365

cmd="find $path_to_examine -mtime -$newer_than"
for file in "${ignored_files[@]}"; do
    cmd="$cmd | grep -v \"$file\""
done
cmd="$cmd | wc -l"
echo "Running: $cmd"
num_active_files=`$cmd`
echo "num files modified less than $newer_than days ago: $num_active_files"

Output if I run that program:

# ./test2.sh 
Running: find /tmp/ -mtime -365 | grep -v "file1" | grep -v "file2" | grep -v "file3" | wc -l
find: bad option |
find: [-H | -L] path-list predicate-list
# 

Output if I run that cmd:

# num=`find /tmp/ -mtime -365 | grep -v "file1" | grep -v "file2" | grep -v "file3" | wc -l`
# echo $num
10
# 

解决方案

You must use the eval command:

num_active_files=`eval $var`

This allows you to generate an expression for bash to run dynamically.

Hope this helps =)

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