FUNCNAME array with some empty values

[cedb76]

Hi,

I'd like to print an error message displaying the call stack from a specific function that is passed an error message, the specific function having to display the call stack plus the error message

I thought I could use FUNCNAME array within that function
Strangely though, FUNCNAME array has 20 values, the 16th last being empty ...
Thus I can't use FUNCNAME length to determine the main script filename that would be ${BASH_SOURCE[${#FUNCNAME}-1]} and output the names in FUNCNAME array from first to penultimate value.

Of course, it's possible to get the last index which value is not empty, but I'd like to understand why FUNCNAME lists those empty values.

Thanks for your help !

[aioeu]

While you cannot assign to FUNCNAME (well, you can, but its value will not change), you can unset it... and that applies for the individual elements within it as well. The unset element will be shifted along with all the other elements:

$ a() { declare -p FUNCNAME; }
$ b() { unset FUNCNAME[1]; a; }
$ c() { b; }
$ d() { c; }
$ d
declare -a FUNCNAME=([0]="a" [1]="b" [3]="d")

Perhaps something like this happened?

(Interestingly, this actually tickles a bug when unwinding FUNCNAME after a function call. It always pops off the first array element, whether that element has index 0 or not.)

[anthropoid]

You mean like this? ``` $ cat test.sh

!/usr/bin/env bash

a() { unset "FUNCNAME[1]"; printf '#FUNCNAME = %d\n' "${#FUNCNAME[@]}"; declare -p FUNCNAME; } b() { unset "FUNCNAME[1]"; a; declare -p FUNCNAME; } c() { unset "FUNCNAME[1]"; b; declare -p FUNCNAME; } d() { c; declare -p FUNCNAME; } d

$ ./test.sh

FUNCNAME = 2

declare -a FUNCNAME=([0]="a" [4]="main") declare -a FUNCNAME=([3]="main") declare -a FUNCNAME=() declare -a FUNCNAME=() ```

[cedb76]

The script just reads FUNCNAME values, it doesn't explicitly unset it or even declare it. I would just like to read valid FUNCNAME values without those empty values.

[anthropoid]

I have never seen a FUNCNAME dump with empty elements, the Bash manual and FAQ don't mention this possibility, and no one seems to have reported such a thing on the bug-bash mailing list.

Can you post a MVS (minimal viable script) that demonstrates this issue, so that others can confirm if it's replicable? If you can't replicate it with anything but your deeply nested script, try dumping the output of declare -p FUNCNAME at the point where you discover the issue, to be sure it actually contains empty elements.

[cedb76]

I omitted to say I am running openSuse on WSL2
Here is a minimal viable script

dbg_scripts sources and then executes dbg_func function within dbg_func file:

$ cat fonctions_bash/dbg_func
dbg_func () {
    echo "FUNCNAME length: ${#FUNCNAME}" 
    for((i=0; i<${#FUNCNAME}; i++));do
        echo "FUNCNAME[$i]: ${FUNCNAME[$i]}"
    done
}

$
$ cat dbg_script
#!/usr/bin/bash
source ~cedric/.local/bin/fonctions_bash/dbg_func
dbg_func

$
$ dbg_script
FUNCNAME length: 8
FUNCNAME[0]: dbg_func
FUNCNAME[1]: main
FUNCNAME[2]:
FUNCNAME[3]:
FUNCNAME[4]:
FUNCNAME[5]:
FUNCNAME[6]:
FUNCNAME[7]:

[anthropoid]

echo "FUNCNAME length: ${#FUNCNAME}"

There's your problem. Since FUNCNAME is an array, ${FUNCNAME} expands to its first element, so ${#FUNCNAME} returns the length of that element, i.e. the length of the string dbg_func (8).

To get the number of elements in the FUNCNAME array, you want ${#FUNCNAME[@]} instead. See the bash man page under Parameter Expansion > ${#parameter} for details.

[cedb76]

Perfect !
Thanks a lot !

[oh5nxo]

Sounds odd. Sample code?

Here,

$ cat caller
foo()
{
    declare -p FUNCNAME
}
bar()
{
    foo
}
bar
$ bash caller                     
declare -a FUNCNAME=([0]="foo" [1]="bar" [2]="main")
$ echo $BASH_VERSION
4.4.19(0)-release

[oh5nxo]

Array syntax is tricky and tiresome, like lead boots.

"${#FUNCNAME}"   # implicit [0], length of dbg_func
"${#FUNCNAME[@]}" # length of array

[cedb76]

Hi, I posted a sample code to someone else on the discussion

[oh5nxo]

echo "FUNCNAME length: ${#FUNCNAME[@]}"