需要在 bash 脚本中创建文件

Question

I have to run a command in a script as a non-root user, or the command won't run. However once this is done, I need the subsequent file to be chown'd to the root user. However, I'm not sure what is the "correct" or best method of doing this. Sample:

 sudo -u $usr db export --path="${htmldir}"/ "/home/zzz/backups/${url}_${st}_$(date '+%Y-%m-%d-%H-%M-%S').sql"

Basically the above has various variable substitutions. I'm also adding a timestamp to the file. What would be the best way to chown that file that has just been created, as it has a timestamp - which could be different if I ran a:

chown root:root "/home/zzz/backups/${url}_${st}_$(date '+%Y-%m-%d-%H-%M-%S').sql"

How do I run a command and place part of that command in a variable - the output file name?

Answer 1

You should only run the date command once, and store the result in a variable. You could either store just the date:

curr_date="$(date '+%Y-%m-%d-%H-%M-%S')"
sudo -u $usr db export --path="${htmldir}"/ "/home/zzz/backups/${url}_${st}_${curr_date}.sql"
chown root:root "/home/zzz/backups/${url}_${st}_${curr_date}.sql"

...or save the entire file path in a variable:

sql_file="/home/zzz/backups/${url}_${st}_$(date '+%Y-%m-%d-%H-%M-%S').sql"
sudo -u $usr db export --path="${htmldir}"/ "$sql_file"
chown root:root "$sql_file"

Personally, I'd prefer the second since it makes it clearer that it's the same file in both places (and harder to goof and use different paths in the two commands). If you needed to use the date for something else as well, I'd actually recommend storing both:

curr_date="$(date '+%Y-%m-%d-%H-%M-%S')"
sql_file="/home/zzz/backups/${url}_${st}_${curr_date}.sql"
sudo -u $usr db export --path="${htmldir}"/ "$sql_file"
chown root:root "$sql_file"
someotherCommand "$curr_date"

Oh, and double-quoting the string on the right side of an assignment is optional, but in lots of other contexts using a variable without double-quotes around it can cause trouble, so I tend to double-quote in assignments just for consistency.

Answer 2

You don't need to use sudo to run the command since you are already root

su -l user -c "db export --path=${htmldir}/ /home/zzz/backups/${url}_${st}_${curr_date}.sql"
chown root:root /home/zzz/backups/${url}_${st}_$(date '+%Y-%m-%d-%H-%M-%S').sql