Cannot access elements of an array in zsh

Question

I am trying to write a script in zsh and I need to make use of arrays in order to achieve my aim in an elegant way. After reading some information over the Net, I tried to implement and access the elements of array in the following way:

### Script for running everything in screens ###
killall -15 screen ## We make sure that no screens are running for now
#bkgarr=(TopJets BosonJets DiBoson TTbar)
bkgarr=(1 2 3)

screen -dmS "MYSCREEN"
screen -S "MYSCREEN" -p 0 -X stuff 'echo "The array has ${#bkgarr[*]} of elements."^M'
screen -S "MYSCREEN" -p 0 -X stuff 'echo ${#bkgarr[0]}^M'

However, this did not work and the output I get is as follows:

~/Summer_Students/nTupler_topness/tupleAnalyzer% echo "The array has ${#bkgarr[*]} of elements."
The array has 0 of elements.
~/Summer_Students/nTupler_topness/tupleAnalyzer% echo ${#bkgarr[0]}
0

Furthermore, I need to have an array of strings like the one commented out in this minimal working example. I would be glad if someone can pinpoint my mistakes and why the array is apparently not stored in computers memory.

Code edit:

### Script for running everything in screens ###
killall -15 screen ## We make sure that no screens are running for now
#bkgarr=(TopJets BosonJets DiBoson TTbar)
bkgarr=(1 2 3)

screen -dmS "MYSCREEN"
screen -S "MYSCREEN" -p 0 -X stuff "$(typeset -p bkgarr)"$'\r'
#screen -S "MYSCREEN" -p 0 -X stuff 'bkgarr=(1 2 3)^M'
screen -S "MYSCREEN" -p 0 -X stuff 'echo "The array has ${#bkgarr[*]} of elements."^M'
screen -S "MYSCREEN" -p 0 -X stuff 'echo ${#bkgarr[0]}^M'

Output afterwards:

~/Summer_Students/nTupler_topness/tupleAnalyzer% declare -a bkgarr='([0]="1" [1]="2" [2]="3")'
declare: bkgarr: can't assign initial value for array
~/Summer_Students/nTupler_topness/tupleAnalyzer% echo "The array has ${#bkgarr[*]} of elements."
The array has 0 of elements.
~/Summer_Students/nTupler_topness/tupleAnalyzer% echo ${#bkgarr[0]}
0
~/Summer_Students/nTupler_topness/tupleAnalyzer%

Thanks in advance

Answer 1

The array is defined in the shell interpreting your script, not the one running in your screen terminal window.

To pass it to your screen window's zsh, try:

screen -S "MYSCREEN" -p 0 -X stuff "$(typeset -p bkgarr)"$'\r'

Note that it will send the newline characters as newline characters, not as carriage returns. That should be fine with zsh though (just the newlines will be inserted in the command line, and not cause to accept the line (which is just as well)).

If your array contains ^C, ", \e characters or other characters special to the terminal or zle or screen's stuff, that won't work though. Same if your shell is not ready to receive that input.

You may want to find another way to pass information to the shell running inside the window, like via a fifo file that is checked as part of the precmd hook.