Code Snippet — August 2, 2026 ### Bash: Parallel Command Runner with Conc

💻 Code Snippet — August 2, 2026

Bash: Parallel Command Runner with Concurrency, Progress & Retry

Replace serial for loops and opaque xargs -P with a pure-Bash runner that gives you live ✓/✗ progress, configurable concurrency, auto-retry with exponential backoff, per-task timeout, fail-fast for CI, and dry-run for safety. Zero dependencies — Bash 4+ only.

# Run commands in parallel (max 2 concurrent, with 3 retries)
par-run -j 2 -r 3 "echo task1" "echo task2" "echo task3"

# From stdin — pipe find/grep results
find . -name "*.py" | par-run --from-stdin -j 8 "python -m pyflakes {}"

# With timeout and fail-fast for CI
par-run -j 4 -t 60 --fail-fast --results ./artifacts/ \\
  "pytest tests/unit/" \\
  "pytest tests/integration/"

# Dry-run first (safety!)
par-run --dry-run -j 4 "rsync -avz /data/ backup:/data/"

Options: -j N (max jobs), -r N (retries), -t SEC (timeout), -f (fail-fast), -d (dry-run), --from-stdin, --results DIR

How it works: Uses wait -n (Bash 4.3+) for true slot-based concurrency — no semaphores, no temp files. As each background job finishes, a slot opens and the next pending task launches. Retry uses exponential backoff: sleep $((2 ** attempt)).

💡 Drop this in ~/.bash_aliases or source it in your Makefile. Full version with self-tests: par-run --test