Task Shell Printf Compatibility

Context: Task (go-task) uses its own minimal shell interpreter, not bash or sh

The Problem

Using printf with dynamic width specifiers (%*s) in Task commands fails with "invalid format char: *" error.

# This fails in Task:
tasks:
  test:
    cmds:
      - |
        padding=10
        printf "%*s%s%*s
" "$padding" "" "text" "$padding" ""

Error output:

invalid format char: *

The formatting.sh library's _center_text function used this pattern:

printf "%*s%s%*s
" "$padding" "" "$text" "$padding" ""

This worked fine when called from bash scripts but failed when called from Task commands.

Root Cause

Task does NOT execute commands using bash or sh. It uses its own built-in minimal shell interpreter for cross-platform portability.

This can be verified:

tasks:
  debug:
    cmds:
      - |
        echo "SHELL: $SHELL"
        echo "BASH_VERSION: $BASH_VERSION"
        if [ -n "$BASH_VERSION" ]; then
          echo "Running in: bash"
        else
          echo "Running in: task"
        fi

Output:

SHELL: /bin/zsh
BASH_VERSION:
Running in: task

Task's shell interpreter supports basic POSIX features but NOT bash-specific features like %* printf format specifier.

Initial Attempted Fixes (Didn't Work)

Added quotes to variables:

printf "%*s%s%*s
" "$padding" "" "$text" "$padding" ""

Added tput fallbacks:

local term_width=$(tput cols 2>/dev/null || echo 80)

These were good defensive practices but didn't solve the core problem since Task's shell doesn't support %*.

The Solution

Abstract complex bash operations to dedicated scripts instead of inline Task commands.

Before (heredoc workaround):

tasks:
  run-updates:
    cmds:
      - |
        bash <<'EOF'
        source "$HOME/dotfiles/platforms/common/.local/shell/formatting.sh"
        print_title "Update All" "cyan"
        task apt:update
        # ... more commands
        EOF

After (clean script):

# management/scripts/update-wsl.sh
#!/usr/bin/env bash
set -euo pipefail

source "$DOTFILES_DIR/platforms/common/.local/shell/formatting.sh"

print_title "WSL Ubuntu Update All" "cyan"
print_banner "Step 1/6 - System Packages" "cyan"
task wsl:apt:update
# ... more steps

# Taskfile.yml
tasks:
  run-updates:
    cmds:
      - bash {{.DOTFILES_DIR}}/management/scripts/update-wsl.sh

Key Learnings

Use dedicated bash scripts when commands require bash-specific features like printf format specifiers, arrays, associative arrays, or advanced string manipulation.

Task commands should orchestrate workflows, not contain complex bash logic.

Task's built-in shell is minimal by design for cross-platform compatibility - it's not bash or sh.

The %* printf format specifier is a GNU/bash extension not available in POSIX sh or Task's interpreter.

When sourcing bash libraries with advanced features from Task, wrap in bash <<'EOF' or use dedicated scripts.

References