变量作为 Bash 脚本中的命令 [英] Variables as commands in Bash scripts

问题描述

我正在编写一个非常简单的 Bash 脚本，它tars 给定目录, 对其输出进行加密，然后将生成的文件拆分为多个较小的文件，因为备份媒体不支持大文件.

I am writing a very simple Bash script that tars a given directory, encrypts the output of that, and then splits the resultant file into multiple smaller files since the backup media doesn’t support huge files.

我对 Bash 脚本没有很多经验.我相信我在正确引用我的变量以允许参数中有空格时遇到了问题.脚本如下:

I don't have a lot of experience with Bash scripting. I believe I’m having issues with quoting my variables properly to allow spaces in the parameters. The script follows:

#! /bin/bash

# This script tars the given directory, encrypts it, and transfers
# it to the given directory (likely a USB key).

if [ $# -ne 2 ]
then
    echo "Usage: `basename $0` DIRECTORY BACKUP_DIRECTORY"
    exit 1
fi

DIRECTORY=$1
BACKUP_DIRECTORY=$2
BACKUP_FILE="$BACKUP_DIRECTORY/`date +%Y-%m-%dT%H-%M-%S.backup`"

TAR_CMD="tar cv $DIRECTORY"
SPLIT_CMD="split -b 1024m - "$BACKUP_FILE""

ENCRYPT_CMD='openssl des3 -salt'

echo "$TAR_CMD | $ENCRYPT_CMD | $SPLIT_CMD"

$TAR_CMD | $ENCRYPT_CMD | $SPLIT_CMD

say "Done backing up"

运行此命令失败:

拆分:foo/2009-04-27T14-32-04.backup"aa:没有那个文件或目录

split: "foo/2009-04-27T14-32-04.backup"aa: No such file or directory

我可以通过删除设置 $SPLIT_CMD 的 $BACKUP_FILE 周围的引号来修复它.但是，如果我的备份目录的名称中有空格，则它不起作用.此外，如果我复制并粘贴回声"的输出命令直接进入终端，它工作正常.很明显，我不明白 Bash 是如何逃避事物的.

I can fix it by removing the quotes around $BACKUP_FILE where I set $SPLIT_CMD. But, if I have a space in the name of my backup directory, it doesn't work. Also, if I copy and paste the output from the "echo" command directly into the terminal, it works fine. Clearly there's something I don't understand about how Bash is escaping things.

推荐答案

不要将整个命令放在变量中.尝试恢复引用的参数会遇到很多麻烦.

Simply don't put whole commands in variables. You'll get into a lot of trouble trying to recover quoted arguments.

还有:

1. 避免在脚本中使用全大写的变量名.这是一种用脚射击自己的简单方法.
2. 不要使用反引号.使用 $(...) 代替；它可以更好地嵌套.

---

#! /bin/bash

if [ $# -ne 2 ]
then
    echo "Usage: $(basename $0) DIRECTORY BACKUP_DIRECTORY"
    exit 1
fi

directory=$1
backup_directory=$2
current_date=$(date +%Y-%m-%dT%H-%M-%S)
backup_file="${backup_directory}/${current_date}.backup"

tar cv "$directory" | openssl des3 -salt | split -b 1024m - "$backup_file"

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