Lets you probe and test for shell capabilites.

Results

========== bash ==========

--- plain mode (bash ) ---
HAS_PIPEFAIL    = 1
HAS_ARRAY       = 1
HAS_EUO         = 1
HAS_EVAL        = 1
HAS_ASSOC_ARRAY = 1
HAS_DBLBRACK    = 1

--- interactive mode (bash -i) ---
HAS_PIPEFAIL    = 1
HAS_ARRAY       = 1
HAS_EUO         = 1
HAS_EVAL        = 1
HAS_ASSOC_ARRAY = 1
HAS_DBLBRACK    = 1

--- login+interactive mode (bash -il) ---
Welcome to Cloud Shell! Type "help" to get started.
To set your Cloud Platform project in this session use `gcloud config set project [PROJECT_ID]`.
You can view your projects by running `gcloud projects list`.
HAS_PIPEFAIL    = 1
HAS_ARRAY       = 1
HAS_EUO         = 1
HAS_EVAL        = 1
HAS_ASSOC_ARRAY = 1
HAS_DBLBRACK    = 1

========== zsh ==========

--- plain mode (zsh ) ---
HAS_PIPEFAIL    = 1
HAS_ARRAY       = 0
HAS_EUO         = 1
HAS_EVAL        = 1
HAS_ASSOC_ARRAY = 1
HAS_DBLBRACK    = 1

--- interactive mode (zsh -i) ---
HAS_PIPEFAIL    = 1
HAS_ARRAY       = 0
HAS_EUO         = 1
HAS_EVAL        = 1
HAS_ASSOC_ARRAY = 1
HAS_DBLBRACK    = 1

--- login+interactive mode (zsh -il) ---
HAS_PIPEFAIL    = 1
HAS_ARRAY       = 0
HAS_EUO         = 1
HAS_EVAL        = 1
HAS_ASSOC_ARRAY = 1
HAS_DBLBRACK    = 1

========== sh ==========

--- plain mode (sh ) ---
HAS_PIPEFAIL    = 1
HAS_ARRAY       = 1
HAS_EUO         = 1
HAS_EVAL        = 1
HAS_ASSOC_ARRAY = 1
HAS_DBLBRACK    = 1

--- interactive mode (sh -i) ---
HAS_PIPEFAIL    = 1
HAS_ARRAY       = 1
HAS_EUO         = 1
HAS_EVAL        = 1
HAS_ASSOC_ARRAY = 1
HAS_DBLBRACK    = 1

--- login+interactive mode (sh -il) ---
Welcome to Cloud Shell! Type "help" to get started.
To set your Cloud Platform project in this session use `gcloud config set project [PROJECT_ID]`.
You can view your projects by running `gcloud projects list`.
HAS_PIPEFAIL    = 1
HAS_ARRAY       = 1
HAS_EUO         = 1
HAS_EVAL        = 1
HAS_ASSOC_ARRAY = 1
HAS_DBLBRACK    = 1

test.sh

tee x.sh >/dev/null <<'EOF'
#!/usr/bin/env sh
# ── probe six core capabilities (each one-liner is side-effect free) ──
( set -o pipefail           ) 2>/dev/null && HAS_PIPEFAIL=1 || HAS_PIPEFAIL=0
( foo=(); foo[0]=x          ) 2>/dev/null && HAS_ARRAY=1    || HAS_ARRAY=0
( set -euo pipefail; :      ) 2>/dev/null && HAS_EUO=1      || HAS_EUO=0
( eval :                    ) 2>/dev/null && HAS_EVAL=1     || HAS_EVAL=0
( typeset -A _A 2>/dev/null ) 2>/dev/null && HAS_ASSOC_ARRAY=1 || HAS_ASSOC_ARRAY=0
( [[ 1 -eq 1 ]]             ) 2>/dev/null && HAS_DBLBRACK=1 || HAS_DBLBRACK=0

printf 'HAS_PIPEFAIL    = %s\n' "$HAS_PIPEFAIL"
printf 'HAS_ARRAY       = %s\n' "$HAS_ARRAY"
printf 'HAS_EUO         = %s\n' "$HAS_EUO"
printf 'HAS_EVAL        = %s\n' "$HAS_EVAL"
printf 'HAS_ASSOC_ARRAY = %s\n' "$HAS_ASSOC_ARRAY"
printf 'HAS_DBLBRACK    = %s\n' "$HAS_DBLBRACK"
EOF
chmod +x x.sh

# ─── driver that runs x.sh under bash, zsh, sh in plain/interactive/login ───
tee run-matrix.sh >/dev/null <<'EOF'
#!/usr/bin/env bash
PROBE="./x.sh"                                # script to test

shells=(bash zsh sh)                          # add ksh, dash, etc. if desired
modes=("" "-i" "-il")                         # plain, interactive, login+interactive
mode_names=("plain" "interactive" "login+interactive")

for shell in "${shells[@]}"; do
  command -v "$shell" >/dev/null 2>&1 || { echo "⏭  $shell not found"; continue; }
  printf '\n========== %s ==========\n' "$shell"

  for idx in "${!modes[@]}"; do
    mode="${modes[$idx]}"
    label="${mode_names[$idx]}"
    printf '\n--- %s mode (%s %s) ---\n' "$label" "$shell" "$mode"

    if [ -z "$mode" ]; then
      "$shell" "$PROBE"                       # plain script execution
    else
      "$shell" $mode "$PROBE"                 # -i x.sh  or  -il x.sh
    fi
  done
done
EOF

chmod +x run-matrix.sh

. run-matrix.sh