在BASH配置文件中定义变量的最佳实践

Question

I read in http://wiki.bash-hackers.org/howto/conffile that it is recommended to put double quotes around values in BASH configuration files which are to be sourced into a script.

The file to be sourced should be formated in key="value" format, otherwise bash will try to interpret commands

However, I am not aware of any difference in BASH's behavior when sourcing a configuration file if the value has double quotes or not, assuming there is no whitespace in the value. I'm sure there are some more complex cases where the double quotes are vital (eg using other variables as the value), but for the simple cases below, would double quotes cause BASH to behave any differently, even if the difference is only behind-the-scenes? I'm wondering if the first configuration file below could cause BASH to search for a named foobar before assigning it as a string, but from my testing it doesn't appear to do so.

# Configuration file 1
myDir=/var/tmp/test/
myString=foobar
myInteger=20

# Configuration file 2
myDir="/var/tmp/test/"
myString="foobar"
myInteger="20"

source configurationFile1
echo "$myDir"
echo "$myString"
echo "$myInteger"

source configurationFile2
echo "$myDir"
echo "$myString"
echo "$myInteger"

Answer 1

It's a style issue. In the examples you show, the quotes aren't strictly necessary. myDir=/var/tmp/text and myDir="/var/tmp/text" do exactly the same thing. Other values may require quotes to make the assignment correct.

The allusion is to the fact that these aren't really configuration files; they're just bash scripts that are intended to contain only assignments. Something like

foo=bar baz

is not an assignment; it's a simple command that tries to run baz with a variable named foo in its environment. Here, quotes are required:

foo="bar baz"

to make a proper assignment, in contrast to other "actual" configuration file formats where everything following the = (and optionally some post- = whitespace`) is considered part of the value to be assigned.