command substitution breaks command substitution

Question

I extracted part of a shell script into another shell script, and for some reason after calling the sub-script, command substitution stops working. I can't imagine it's something in the sub-script, but I can't see what I'm doing wrong, either.

whether i do:

dirname "$0"                                      # works
echo "`dirname "$0"`"                             # works
echo "$(dirname "$0")"                            # works
cat <<< "`dirname "$0"`"                          # works
cat <<< "$(dirname "$0")"                         # works
"$(dirname "$0")"/setup_buildroot.sh "$BUILDROOT" # call the sub-script
dirname "$0"                                      # works
echo "`dirname "$0"`"                             # empty string
echo "$(dirname "$0")"                            # empty string
cat <<< "`dirname "$0"`"                          # crash
cat <<< "$(dirname "$0")"                         # crash

or i do:

dirname "$0"                                      # works
echo "`dirname "$0"`"                             # works
echo "$(dirname "$0")"                            # works
cat <<< "`dirname "$0"`"                          # works
cat <<< "$(dirname "$0")"                         # works
"`dirname "$0"`"/setup_buildroot.sh "$BUILDROOT"  # call the sub-script
dirname "$0"                                      # works
echo "`dirname "$0"`"                             # empty string
echo "$(dirname "$0")"                            # empty string
cat <<< "`dirname "$0"`"                          # crash
cat <<< "$(dirname "$0")"                         # crash

dirname seems to work fine, but backtick and $() stop working. The command substitution just returns an empty string.

EDIT: removing all the double quotes "" doesn't have an effect

EDIT2: executing bash explicitly when calling the sub-script has no effect

EDIT3: saving "$(dirname "$0")" to a variable and using that has no effect

EDIT4: adding the same echo commands to the sub-script show that everything is fine in the sub-script

EDIT5: as per request, output of script

/home/jayen/rep
/home/jayen/rep
/home/jayen/rep
/home/jayen/rep
/home/jayen/rep
#setup_buildroot.sh output here
/home/jayen/rep


bash: syntax error near unexpected token `newline'
bash: syntax error near unexpected token `newline'

Answer 1

it doesn't make sense, but try sourcing your sub-script

. "$(dirname "$0")"/setup_buildroot.sh "$BUILDROOT" # call the sub-script

Answer 2

I feel like calling the sub-script is breaking the environment variables of your existing bash script's session. Maybe try prefixing the sub-script line with bash, so

bash "`dirname "$0"`"/setup_buildroot.sh "$BUILDROOT"

and see if that fixes the issue. This is an odd situation.

The other solution I recommend is on the first line, do

mydir="$0"

and replace all the $0 with $mydir

and better yet, do

mydir=`dirname "$0"`

up front and not rerun the command over and over.