idioms for returning multiple values in shell scripting

Question

Are there any idioms for returning multiple values from a bash function within a script?

http://tldp.org/LDP/abs/html/assortedtips.html describes how to echo multipl

Answer 1

Later version of Bash supports nameref. Use declare -n var_name to give var_name the nameref attribute. nameref gives your function the ability to "pass by reference" which is commonly used in C++ functions to return multiple values. According to Bash man page:

A variable can be assigned the nameref attribute using the -n option to the declare or local builtin commands to create a nameref, or a reference to another variable. This allows variables to be manipulated indirectly. Whenever the nameref variable is referenced or assigned to, the operation is actually performed on the variable specified by the nameref variable's value. A nameref is commonly used within shell functions to refer to a variable whose name is passed as an argument to the function.

The following are some interactive command line examples.

Example 1:

$ unset xx yy
$ xx=16
$ yy=xx
$ echo "[$xx] [$yy]"
[16] [xx]
$ declare -n yy
$ echo "[$xx] [$yy]"
[16] [16]
$ xx=80
$ echo "[$xx] [$yy]"
[80] [80]
$ yy=2016
$ echo "[$xx] [$yy]"
[2016] [2016]
$ declare +n yy # Use -n to add and +n to remove nameref attribute.
$ echo "[$xx] [$yy]"
[2016] [xx]

Example 2:

$ func()
> {
>     local arg1="$1" arg2="$2"
>     local -n arg3ref="$3" arg4ref="$4"
> 
>     echo ''
>     echo 'Local variables:'
>     echo "    arg1='$arg1'"
>     echo "    arg2='$arg2'"
>     echo "    arg3ref='$arg3ref'"
>     echo "    arg4ref='$arg4ref'"
>     echo ''
> 
>     arg1='1st value of local assignment'
>     arg2='2st value of local assignment'
>     arg3ref='1st return value'
>     arg4ref='2nd return value'
> }
$ 
$ unset foo bar baz qux
$ 
$ foo='value of foo'
$ bar='value of bar'
$ baz='value of baz'
$ qux='value of qux'
$ 
$ func foo bar baz qux

Local variables:
    arg1='foo'
    arg2='bar'
    arg3ref='value of baz'
    arg4ref='value of qux'

$ 
$ {
>     echo ''
>     echo '2 values are returned after the function call:'
>     echo "    foo='$foo'"
>     echo "    bar='$bar'"
>     echo "    baz='$baz'"
>     echo "    qux='$qux'"
> }

2 values are returned after the function call:
    foo='value of foo'
    bar='value of bar'
    baz='1st return value'
    qux='2nd return value'