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Demo Magic

demo-magic.sh is a handy shell script that enables you to script repeatable demos in a bash environment so you don't have to type as you present. Rather than trying to type commands when presenting you simply script them and let demo-magic.sh run them for you.

Features

  • Simulates typing. It looks like you are actually typing out commands
  • Allows you to actually run commands or pretend to do so.
  • Can hide commands from presentation. Useful for behind the scenes stuff that doesn't need to be shown.

Functions

pe

Print and Execute. This function will simulate typing whatever you give it. It will then pause until you press ENTER. After your keypress it will run the command.

#!/bin/bash

pe "ls -l"

p

Print only. This function will simulate typing whatever you give it. It will not run the command. After typing it will pause until you press ENTER. After your keypress it will move on to the next instruction in your script.

#!/bin/bash

p "ls -l"

wait

Waits for the user to press ENTER.

If PROMPT_TIMEOUT is defined and > 0 the demo will automatically proceed after the amount of seconds has passed.

#!/bin/bash

# Will wait until user presses enter
PROMPT_TIMEOUT=0
wait

# Will wait max 5 seconds until user presses
PROMPT_TIMEOUT=5
wait

cmd

Enters script into interactive mode and allows newly typed commands to be executed within the script

#!/bin/bash

cmd

Getting Started

Create a shell script and include demo-magic.sh

#!/bin/bash

########################
# include the magic
########################
. demo-magic.sh

# hide the evidence
clear

# Put your stuff here

Then use the handy functions to run through your demo.

Command line usage

demo-magic.sh exposes 3 options out of the box to your script.

  • -d - disable simulated typing. Useful for debugging
  • -h - prints the usage text
  • -n - set no default waiting after p and pe functions
  • -w - set no wait timeout after p and pe functions
$ ./my-demo.sh -h

Usage: ./my-demo.sh [options]

  Where options is one or more of:
  -h  Prints Help text
  -d  Debug mode. Disables simulated typing
  -n  No wait
  -w  Waits max the given amount of seconds before proceeding with demo (e.g. `-w5`)

Useful Tricks

Faking network connections

Network connections during demos are often unreliable. Try and fake whatever commands would rely on a network connection. For example: Instead of trying to install node modules in a node.js application you can fake it. You can install the node_modules at home on your decent network. Then rename the directory and pretend to install it later by symlinking. If you want to be thorough you can capture the output of npm install into a log file then cat it out later to simulate the install.

#!/bin/bash

########################
# include the magic
########################
. demo-magic.sh

# hide the evidence
clear

# this command is typed and executed
pe "cd my-app"

# this command is merely typed. Not executed
p "npm install"

# this command runs behind the scenes
ln -s cached_node_modules node_modules

# cat out a log file that captures a previous successful node modules install
cat node-modules-install.log

# now type and run the command to start your app
pe "node index.js"

No waiting

The -n no wait option can be useful if you want to print and execute multiple commands.

# include demo-magic
. demo-magic.sh -n

# add multiple commands
pe 'git status'
pe 'git log --oneline --decorate -n 20'

However this will oblige you to define your waiting points manually e.g.

...
# define waiting points
pe 'git status'
pe 'git log --oneline --decorate -n 20'
wait
pe 'git pull'
pe 'git log --oneline --decorate -n 20'
wait