Make Shell Script Hooks Visible with Stderr Redirection

I was setting up Git hooks to auto-sync my project workspace on exit, but I couldn’t see any output. The hook ran silently—no success messages, no errors, nothing. I had no idea if it was even working.

The problem? Hook scripts inherit their parent’s stdout/stderr, but they often run in contexts where those streams are redirected to /dev/null. So even if you echo messages, you’ll never see them.

The Solution: Redirect stderr to stdout, Then Format

To make hook output visible, you need to:

1. Redirect stderr to stdout (2>&1)
2. Pipe through sed to add indentation
3. Redirect back to stderr (>&2) so it appears in the terminal

Here’s the pattern:

#!/bin/bash

# Run your command and make output visible
my-sync-script.sh 2>&1 | sed 's/^/  /' >&2

What’s Happening Here?

• 2>&1 — Merge stderr into stdout (captures all output)
• | sed 's/^/ /' — Add 2 spaces to the start of each line (formatting)
• >&2 — Send the formatted output to stderr (visible in terminal)

Example: Auto-Sync on Git Exit

I used this pattern in a boot script that syncs project files from Google Drive before running:

#!/bin/bash
# ~/.local/bin/sync-workspace.sh

echo "🔄 Syncing workspace from Google Drive..."

rclone sync gdrive:workspace /local/workspace \
    --fast-list \
    --transfers 8 \
    2>&1 | sed 's/^/  /' >&2

echo "✅ Workspace synced"

Now when the script runs, I see:

🔄 Syncing workspace from Google Drive...
  Transferred: 1.2 MiB / 1.2 MiB, 100%
  Checks: 47 / 47, 100%
✅ Workspace synced

When to Use This

• Git hooks (pre-commit, post-checkout, etc.)
• Boot scripts that run on system startup
• Cron jobs where you want output logged
• Any background process where visibility helps debugging

Without this pattern, your hooks run silently. With it, you get clear feedback—success messages, error details, everything.