Portable Shell Boundaries

Feature Guard

Choose Bash or Plain Lists

A script can isolate Bash-only features behind a small decision so the portable path remains visible and testable.

Program

Play the script to choose a shell mode and see which list representation the script plans to use.

shell_mode
feature_guard.sh
Replay: real traced execution (multi-file project)
#!/usr/bin/env bash

shell_mode="bash"
if [ "$shell_mode" = "bash" ]; then
    list_style="array"
else
    list_style="newline-list"
fi
echo "$shell_mode:$list_style"

#!/usr/bin/env bash

shell_mode="sh"
if [ "$shell_mode" = "bash" ]; then
    list_style="array"
else
    list_style="newline-list"
fi
echo "$shell_mode:$list_style"

  1. shell_mode ← bash

    3shell_mode="bash"4if [ "$shell_mode" = "bash" ]; then
    values this stepbashshell_mode

  2. if [ "$shell_mode" = "bash" ]; then

    3shell_mode="bash"4if [ "$shell_mode" = "bash" ]; then5    list_style="array"
    values this stepbashshell_mode

  3. list_style ← array

    4if [ "$shell_mode" = "bash" ]; then5    list_style="array"6else
    values this steparraylist_style

  4. echo "$shell_mode:$list_style"

    8fi9echo "$shell_mode:$list_style"
    outputbash:array
    values this stepbashshell_modearraylist_style

  1. shell_mode ← sh

    3shell_mode="sh"4if [ "$shell_mode" = "bash" ]; then
    values this stepshshell_mode

  2. if [ "$shell_mode" = "bash" ]; then

    3shell_mode="sh"4if [ "$shell_mode" = "bash" ]; then5    list_style="array"
    values this stepshshell_mode

  3. list_style ← newline-list

    6else7    list_style="newline-list"8fi
    values this stepnewline-listlist_style

  4. echo "$shell_mode:$list_style"

    8fi9echo "$shell_mode:$list_style"
    outputsh:newline-list
    values this stepshshell_modenewline-listlist_style
feature guard A guard keeps a Bash-only choice explicit instead of scattering assumptions through the script.
array boundary Arrays are Bash features; POSIX `sh` scripts often use newline-delimited text instead.
mode label A clear label makes the selected portability path visible in logs and tests.