在 bash 中，如何在字符串中插入 $(...)？
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In bash, how do I interpolate $(...) in a string?
提问by Hoytman
I am attempting to write a bash script that performs a mysqldump on my live site's database, then adds and commits the dump to a git repository. Here is what I have so far (stored in a .sh file which is called by a crontab entry):
我正在尝试编写一个 bash 脚本，该脚本在我的实时站点的数据库上执行 mysqldump，然后将转储添加并提交到 git 存储库。这是我到目前为止所拥有的（存储在由 crontab 条目调用的 .sh 文件中）：
/usr/bin/mysqldump --skip-comments --skip-dump-date -u [user] -p[pass] database | gzip > /var/www/site/backup/database.sql.gz
cd var/www/site/backup && git add *
cd var/www/site/backup && git commit -m 'Database $(date +%a %H:%M %h %d %Y)'
My crontab entry looks like this:
我的 crontab 条目如下所示：
0,20,40 8-22 * * * /var/www/site/backup/script.sh
I can see that this script does dump the database, but does not add or commit the file to git. Is there something that I am missing?
我可以看到这个脚本确实转储了数据库，但没有将文件添加或提交到 git。有什么我想念的吗？
Edit =================================
编辑 ================================
I made the following changes and the commit works:
我进行了以下更改并且提交有效：
cd /var/www/site/backup && /usr/bin/git add *
cd /var/www/site/backup && /usr/bin/git commit -m 'Database $(date +%a %H:%M %h %d %Y)'
However, the date does not get calculated.
但是，不会计算日期。
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Latest Revisions, including (most of) the recommendations
最新修订，包括（大部分）建议
/usr/bin/mysqldump --skip-comments --skip-dump-date -u [user] -p[pass] database > /var/www/site/backup/database.sql
cd var/www/site/backup
/usr/bin/git add *
/usr/bin/git commit -m "Internal Forms Live Database Dump Stored $(date '+%a %H:%M %h %d %Y')"
回答by kostix
$(...)and other forms of substitutions are not interpolated in single-quoted strings.
$(...)和其他形式的替换不会插入到单引号字符串中。
So if you want your date calculated, do
所以如果你想计算你的日期，做
git commit -m "Database $(date '+%a %M:%H %h %d %Y')"
that is, the whole message string is double-quoted to allow $(...)to be interpolated while the argument to dateis in single quotes to make it a single argument (passed to date).
也就是说，整个消息字符串被双引号括起来以允许$(...)插入，而 to 的参数date在单引号中以使其成为单个参数（传递给date）。
