Array job gives error in bash - arrays

Question

As I want to run several simulations with different values in R, I have been recommended to use a job array in bash.
1) I generated the combination of parameters and saved it in a txt file, called parameters.txt.
2) I want now to use each combination of parameters into R. Each combination is represented by a line of 3 numbers (the 3 parameters) in parameters.txt.
When I run my script, an error message appears :
head: parameters.txt: invalid number of lines
head: parameters.txt: invalid number of lines
head: parameters.txt: invalid number of lines
Job array item : rx=, ry=, rz=
Here is my script:
# Sweeping parameters.txt
N=${SLURM_ARRAY_TASK_ID}
rx=`head -n ${N} parameters.txt | tail -n 1 | cut -d' ' -f1`
ry=`head -n ${N} parameters.txt | tail -n 1 | cut -d' ' -f2`
rz=`head -n ${N} parameters.txt | tail -n 1 | cut -d' ' -f3`
# Display
echo "Job array item $N: rx=$rx, ry=$ry, rz=$rz"
echo "---------------------------------"
# Run
R CMD BATCH ex.R $rx $ry $rz

Answer 1

Seems SLURM_ARRAY_TASK_ID is None (not set) and as a result N is None here:
N=${SLURM_ARRAY_TASK_ID}
Then bash translates it as
rx=`head -n parameters.txt ...
You can wrap with if statement as follows:
N=${SLURM_ARRAY_TASK_ID}
if [ -n "${N}" ]; then
rx=`head -n ${N} parameters.txt | tail -n 1 | cut -d' ' -f1`
ry=`head -n ${N} parameters.txt | tail -n 1 | cut -d' ' -f2`
rz=`head -n ${N} parameters.txt | tail -n 1 | cut -d' ' -f3`
# Display
echo "Job array item $N: rx=$rx, ry=$ry, rz=$rz"
echo "---------------------------------"
# Run
R CMD BATCH ex.R $rx $ry $rz
else
echo "SLURM_ARRAY_TASK_ID / N is None"
fi