Session 1 - Introduction

Topics

  • Development environment
  • CLI basics review
  • Hello World!
  • Variables / Arguments
  • Tests / Conditions
  • Loops
  • Dos & Donts

CLI basics review

  • Change Directory: cd
  • List Directory: ls / dir
  • Remove / Delete: rm / del
  • Copy: cp / copy
  • Clear Screen: clear / cls
  • Write output: echo
  • Quit: exit

See: DOS to Linux Cheat Sheet (kh.edu.tw)

An Editor

Atom Editor
Atom Editor

First Words?

Hello world!

“[A ‘Hello World’ program] is very simple in most programming languages, and is often used to illustrate the basic syntax of a programming language. It is often the first program written by people learning to code.”

First Words

Batch file:

echo Hello world!

First Words

Batch file:

    @echo off
    cls
    echo Hello world!
    @pause

Shell script:

    clear
    echo "Hello world!"
    read -p "Press return to continue..."

Let’s do it!

FFmpeg on this!

Variables

Batch file:

SET FFMPEG=C:\ffmpeg\bin\ffmpeg.exe
echo %FFMPEG%

Shell script:

FFMPEG="/usr/bin/ffmpeg"
echo "$FFMPEG"

Arguments / Parameters

Batch file:

echo %1
echo %2
echo %3

Shell script:

echo $1
echo $2
echo $3

Arguments / Parameters

Batch file:

SET "VID_IN=%1"
echo %VID_IN%

Shell script:

VID_IN="$1"
echo "$VID_IN"

Tests / Conditions

Batch file:

IF "%1"=="" GOTO ERROR_EmptyParam
goto End

:ERROR_EmptyParam
echo "ouch."

:End

Tests / Conditions

Batch file:

IF NOT EXIST %FFMPEG% GOTO ERROR_FFmpegNotFound
GOTO End

:ERROR_FFmpegNotFound
echo "This is sad."

:End

End

Homework (1 of 2)

Improve FFmpeg helper script:

  • Allow to choose video codec like this: $ ffmpeg_helper.bat VIDEO_IN codec CODEC
  • So “codec” is an additional “ANWENDUNGSFALL” with an additional argument.
  • The previous functionality shall be preserved.
  • Think of an English term for “ANWENDUNGSFALL” (Why? Next session ;))

Homework (2 of 2)

Try to read and understand a real-world script:

  • Download and open (do not execute!): “start.bat”
  • What does it seem to be for?
  • Roughly, what cases does it deal with?
  • If executed, which arguments does it expect?
  • How could a valid commandline for this script look like?