VERSION_VALUE=$( function2 "$MY_TEMPFILE" "a_string" "another_string" | not_important_function_b )

#!/bin/bash
# FILE : file2
#
function function_2 {
not_important_function_c "$1"  "$2" "$3"
if [[ ! -z "$3" ]] ; then
CODE_ERR = 0
echo "GOOD_VALUE"
else
CODE_ERR = 1
fi
CODE_ERR = 2

retrun $CODE_ERR  # always return 2
}

#!/bin/bash
# FILE : file1
#
function function_1 {
#
    MY_TEMPFILE=$(mktemp)
    CODE_ERR_GLOB=$?  # never fail --> 0 success
#
    not_important_function_a "$1"  "$2"  > "$MY_TEMPFILE"
    CODE_ERR=$?  # never fail --> return 0 success
    (( CODE_ERR_GLOB += CODE_ERR ))
#
    VERSION_VALUE=$( function2 "$MY_TEMPFILE" "a_string" "another_string" | not_important_function_b )  
# function2 always fails -> return 2
# not_important_function_b never fails --> return 0 success
    echo "$?"
    CODE_ERR=$? # always 0 --> success but function2 fails
    echo "CODE_ERR : $CODE_ERR"
    (( CODE_ERR_GLOB += CODE_ERR ))
    echo "CODE_ERR_GLOB : $CODE_ERR_GLOB"
#
    rm -f $MY_TEMPFILE > /dev/null 2>&1
    CODE_ERR=$? # always 0 --> success but function2 fails
    (( CODE_ERR_GLOB += CODE_ERR ))
#
    if [[ $CODE_ERR_GLOB -eq 0  ]] ; then
        echo $VERSION_VALUE # echo a good value if no error nowhere
    fi
#
    return $CODE_ERR_GLOB always success but function2 fails
#
}

#!/bin/bash
#
#Main_program
#
source file1
source file 2
source file 3
#
MY_DATA=$(function_1 "param1" "param2" "param3")
ERR_CODE=$?     # always = 0 ! ! ! ! !
if [[  $ERR_CODE -ne 0 ]] ; then
echo "Error from function 1" # never print this
else
echo "Good data : $MY_DATA"
fi