Lesson 10: Redundant Action Calls — Doing the Same Thing Twice

File affected: scripts/playerctl.sh Severity: Medium — play and pause commands issue two playerctl calls instead of one

---

What Happened

main() {
    case "$MODE" in
        play|pause|stop)
            play_pause          # <-- always toggles play/pause
            if [[ "$MODE" == "play" ]]; then play       # <-- then explicitly plays
            elif [[ "$MODE" == "pause" ]]; then pause   # <-- or explicitly pauses
            else stop
            fi
            ;;

When MODE=play, the code: 1. Calls play_pause → playerctl play-pause (toggles) 2. Then calls play → playerctl play (plays again)

If the player was already playing, step 1 pauses it, then step 2 immediately plays it again — net result is no change, but with two IPC round-trips.

If the player was paused, step 1 plays it, then step 2 plays it again (no-op, but still wasteful).

The play_pause call was clearly copied from the play-pause branch and left in by mistake. The play|pause|stop branch should call only the specific action:

The Fix

main() {
    case "$MODE" in
        play)
            play
            ;;
        pause)
            pause
            ;;
        stop)
            stop
            ;;
        play-pause)
            play_pause
            ;;

The General Pattern

This is the "action + redundant side-effect" pattern:

# BAD — the outer action is a superset of the inner ones
case "$MODE" in
    a|b|c)
        do_all_three   # runs regardless of which branch
        if [[ "$MODE" == "a" ]]; then do_a; fi
        if [[ "$MODE" == "b" ]]; then do_b; fi
        ;;

Should be:

# GOOD — each branch does exactly what it says
case "$MODE" in
    a)  do_a ;;
    b)  do_b ;;
    c)  do_c ;;

Secondary: the play_pause Function Name Is Misleading

play_pause runs playerctl play-pause (a toggle). But it reads like "play and pause at the same time." A clearer name is toggle_playback or play_pause_toggle. Misleading function names are a common reason copy-paste bugs like this survive code review — the reader assumes it's doing something it isn't.

How to Catch It

Look for case arms that call a function before dispatching into per-branch logic:

grep -A 10 'case "\$MODE"' scripts/playerctl.sh

If a function call appears before the if/elif chain inside a case arm, ask: "Is this call intentional, or was it copied from a sibling branch?"