How to use a variable's value as another varia

问题:

This question already has an answer here:

• Dynamic variable names in Bash 10 answers

I want to declare a variable, the name of which comes from the value of another variable, and I wrote the following piece of code:

a=\"bbb\"
$a=\"ccc\"

but it didn\'t work. What\'s the right way to get this job done?

回答1:

eval is used for this, but if you do it naively, there are going to be nasty escaping issues. This sort of thing is generally safe:

name_of_variable=abc

eval $name_of_variable=\"simpleword\"   # abc set to simpleword

This breaks:

eval $name_of_variable=\"word splitting occurs\"

The fix:

eval $name_of_variable=\"\\\"word splitting occurs\\\"\"  # not anymore

The ultimate fix: put the text you want to assign into a variable. Let\'s call it safevariable. Then you can do this:

eval $name_of_variable=\\$safevariable  # note escaped dollar sign

Escaping the dollar sign solves all escape issues. The dollar sign survives verbatim into the eval function, which will effectively perform this:

eval \'abc=$safevariable\' # dollar sign now comes to life inside eval!

And of course this assignment is immune to everything. safevariable can contain *, spaces, $, etc. (The caveat being that we\'re assuming name_of_variable contains nothing but a valid variable name, and one we are free to use: not something special.)

回答2:

You can use declare and !, like this:

John=\"nice guy\"
programmer=John
echo ${!programmer} # echos nice guy

Second example:

programmer=Ines
declare $programmer=\"nice gal\"
echo $Ines # echos nice gal

回答3:

This might work for you:

foo=bar
declare $foo=baz
echo $bar
baz

or this:

foo=bar
read $foo <<<\"baz\"
echo $bar
baz

回答4:

You could make use of eval for this.
Example:

$ a=\"bbb\"
$ eval $a=\"ccc\"
$ echo $bbb
ccc

Hope this helps!

回答5:

If you want to get the value of the variable instead of setting it you can do this

var_name1=\"var_name2\"
var_name2=value_you_want
eval temp_var=\\$$var_name1
echo \"$temp_var\"

You can read about it here indirect references.

回答6:

You can assign a value to a variable using simple assignment using a value from another variable like so:

#!/usr/bin/bash

#variable one
a=\"one\"

echo \"Variable a is $a\"
#variable two with a\'s variable
b=\"$a\"

echo \"Variable b is $b\"

#change a
a=\"two\"
echo \"Variable a is $a\"
echo \"Variable b is $b\"

The output of that is this:

Variable a is one
Variable b is one
Variable a is two
Variable b is one

So just be sure to assign it like this b=\"$a\" and you should be good.