Lesson 15: Unquoted Line Continuation in Command Substitution¶

File affected: scripts/actions/clipboard.sh Severity: High — select_and_paste always fails; fuzzel is never invoked

What Happened¶

select_and_paste() {
  if command -v cliphist &>/dev/null; then
    local selected
    if command -v fuzzel &>/dev/null; then
      selected=$(cliphist list | fuzzel --dmenu --theme="$HOME/.config/fuzzel/fuzzel.ini" 
          --prompt "Clipboard" --placeholder "Search clipboard history..." 
          --match-mode="fuzzy" --width 400 --height 300)

The command substitution $(...) spans three visual lines, but there are no continuation backslashes (\). In bash, a newline inside $(...) terminates the command — it does not automatically continue to the next line.

So the shell sees:

fuzzel --dmenu --theme="..."

then a newline, which ends the fuzzel command. The remaining two lines:

    --prompt "Clipboard" --placeholder "..." 
    --match-mode="fuzzy" --width 400 --height 300

are parsed as a new command at the top level of the function body — bare words that are not a valid command. The whole function body fails to parse.

With set -euo pipefail, the script exits. Without it, selected is empty and the paste silently does nothing.

The Fix¶

Add backslash line continuations inside the command substitution:

selected=$(cliphist list | fuzzel --dmenu \
    --theme="$HOME/.config/fuzzel/fuzzel.ini" \
    --prompt "Clipboard" \
    --placeholder "Search clipboard history..." \
    --match-mode="fuzzy" \
    --width 400 \
    --height 300)

Or put it on one line:

selected=$(cliphist list | fuzzel --dmenu --theme="$HOME/.config/fuzzel/fuzzel.ini" --prompt "Clipboard" --width 400 --height 300)

The General Rule¶

Inside $(...), $(( )), [[ ]], and (( )), newlines end the current command. They do NOT automatically continue the command on the next line. You must use \ to continue, or keep the command on one line.

# BAD — newline terminates the command early
result=$(some-command --flag-one
    --flag-two
    --flag-three)

# GOOD — explicit continuation
result=$(some-command --flag-one \
    --flag-two \
    --flag-three)

# ALSO GOOD — single line
result=$(some-command --flag-one --flag-two --flag-three)

This also applies to pipelines:

# BAD — pipe on next line is a new command, not a continuation
result=$(grep "pattern" file
    | sort
    | head -5)

# GOOD — pipe at end of line continues
result=$(grep "pattern" file \
    | sort \
    | head -5)

# ALSO GOOD — pipe at start with backslash
result=$(grep "pattern" file |
    sort |
    head -5)   # trailing pipe continues the expression — no backslash needed

How to Catch It¶

bash -n scripts/actions/clipboard.sh
# Syntax errors from unintended line breaks appear here

shellcheck scripts/actions/clipboard.sh
# SC1078: double-quote mismatch, SC1079: unexpected token

Also: any $( with a multi-line body that lacks \ at every non-final line is a candidate for this bug.