Capture Real Command Output with Exec

In this tutorial, you'll record a real git workflow showing actual command output. Unlike the typing demo tutorial where we simulated typing, here you'll execute actual commands and capture their real output.

Your finished recording will show:

1. Checking git status
2. Creating a new file
3. Staging and committing the changes
4. Viewing the commit log

This is perfect for creating accurate documentation, demos, and tutorials showing real tool behavior. This tutorial takes about 20 minutes.

Prerequisites

You should complete the Typing Demo tutorial first to understand basic VCR# concepts.

You'll also need:

• Git installed and configured
• A test repository (we'll create one)
• About 20 minutes

Step 1: Create a Test Repository

First, let's create a test git repository to work with:

mkdir vcr-git-demo
cd vcr-git-demo
git init
git config user.name "Demo User"
git config user.email "demo@example.com"

Create a tape file called git-workflow.tape:

Output git-workflow.gif
  
Set Cols 100
Set Rows 30
Set Theme "Dracula"
Set Shell "bash"

We're ready to record real commands.

Step 2: Execute Your First Real Command

Add this line to git-workflow.tape:

Exec "git status"
Sleep 1s

Run the recording:

vcr git-workflow.tape

Open the GIF. Notice something different from the typing demo: nothing is "typed" — the real git status output from your repository simply appears.

Unlike Type, which simulates keystrokes, Exec runs a real program and captures its actual output. All Exec commands in a tape run together as a startup script when the shell launches, and their output is recorded as it appears. After the tape's commands finish, VCR# waits for the terminal output to settle (controlled by InactivityTimeout) before ending the recording. Here's a simple example using dotnet --version:

Step 3: Chain Multiple Commands

Update your tape file to create and commit a file:

Output git-workflow.gif
  
Set Cols 100
Set Rows 30
Set Theme "Dracula"
Set Shell "bash"
  
Exec "git status"
Sleep 500ms
  
Exec "echo 'Hello from VCR#' > README.md"
Sleep 500ms
  
Exec "git add README.md"
Sleep 500ms
  
Exec "git commit -m 'Add README'"
Sleep 500ms
  
Exec "git log --oneline -n 1"
Sleep 2s

Run the recording again:

vcr git-workflow.tape

Watch the GIF. The commands run in order within the shell — the file is created, staged, committed, and the commit appears in the log — while VCR# records the real output. The Sleep commands between them pace the recording, holding each result on screen long enough for viewers to read it.

Because the Exec commands run as a single startup script rather than being typed one at a time, the Sleep durations control the recording timeline, not the commands themselves. If you need to hold the recording until specific output appears, use a Wait /pattern/ command (covered next) instead of guessing with Sleep.

Step 4: Wait for Specific Output

Sometimes you want to wait for specific text to appear before continuing. Let's add a Wait command:

Output git-workflow.gif
  
Set Cols 100
Set Rows 30
Set Theme "Dracula"
Set Shell "bash"
  
Exec "git status"
Sleep 500ms
  
Exec "echo 'Hello from VCR#' > README.md"
Sleep 500ms
  
Exec "git add README.md"
Sleep 500ms
  
Exec "git commit -m 'Add README'"
Wait /Add README/
Sleep 500ms
  
Exec "git log --oneline -n 1"
Sleep 2s

Notice the Wait /Add README/ line. Wait takes a regular expression between slashes (not a quoted string), and it pauses the recording until that pattern appears in the terminal output. This is more reliable than a fixed Sleep when output timing varies. (Regex matching is case-sensitive, so the pattern must match the text exactly.)

Run the recording:

vcr git-workflow.tape

The recording works the same, but now it explicitly waits for the commit message to appear. This technique is useful when commands produce output gradually or when timing is unpredictable.

Next Steps

Great work! You've learned to:

• Execute real commands with Exec
• Chain multiple commands in sequence
• Wait for specific output with Wait
• Create accurate recordings of real workflows

You now know both simulated typing (from the typing demo) and real execution.

Complete Code

Here's the full git-workflow.tape file:

Output git-workflow.gif
  
Set Cols 100
Set Rows 30
Set Theme "Dracula"
Set Shell "bash"
  
Exec "git status"
Sleep 500ms
  
Exec "echo 'Hello from VCR#' > README.md"
Sleep 500ms
  
Exec "git add README.md"
Sleep 500ms
  
Exec "git commit -m 'Add README'"
Wait /Add README/
Sleep 500ms
  
Exec "git log --oneline -n 1"
Sleep 2s