OPS102: Windows Scripting

Windows vs. Linux Scripting

• Windows shell scripting is similar to Linux but with different syntax due to different technical heritages.

An Abundance of Shells

• Linux Shells:

  • bash: Widely-deployed shell on Unix-like systems.
  • sh: Original Unix shell (Bourne Shell).
  • ksh: Korn shell.
  • csh: C shell with C-like syntax.
  • fish: Friendly Interactive shell.
  • zsh: Similar to ksh.

• Windows Shells:

  • CMD: Traditional Windows shell with expanded features from DOS.
  • PowerShell: Combines scripting with object-oriented programming. Pre-installed but disabled by default on non-server systems.
  • Focus is on CMD shell scripting in this course.

Cross-Platform Scripting

• Bash/Zsh: Available on Linux and Mac, and as add-ons for Windows.
• PowerShell: Available on Windows by default and on Linux and Mac via third-party options.

Other Interpreted Languages

• Python and Perl: Suitable for cross-platform development.
• Shell scripting is ideal for process control but not for advanced processing algorithms.

Windows "Shell Scripts" vs. Batch Files

• Early scripts known as batch files for non-interactive batch processing.
• Current shell scripts can still use .bat or .cmd extensions.

Basic Requirements for Shell Scripts

1. Create a text file: Use a text editor like Notepad.
2. Shell association via filename extension:
   • CMD scripts: .cmd or .bat
   • PowerShell scripts: .ps1
3. Appropriate permissions: Default permission to read is usually sufficient.

Command Echos

• Windows displays each command before execution.
• Suppress display with @ in front or echo off command.

A Basic Script Example

• Example script using echo and date: @echo off

echo The current date is: date /t

Variables

Setting a Variable

• Use set keyword with variable=value format.
• No spaces around =.
• Variables are untyped.

Accessing a Variable

• Use %VAR_NAME% syntax.

Quoting

• Quoting includes the quotes in most cases.
• Not required when assigning a string with spaces.

Carat Symbols

• Use ^ to escape special characters.

Environment Variables

• All variables are environment variables.
• Use set command to view current variables.

Common Environment Variables

• Examples include CD, TIME, DATE, ERRORLEVEL, etc.

Reading Variable Values from STDIN

• Use set /p to prompt user for input.

Arithmetic

• CMD performs integer arithmetic.
• Use set /A for arithmetic operations.

Conditional Logic: IF/ELSE

• Use IF to control command execution based on tests.
• Types of tests include file existence, string equality, numeric comparisons, and variable definition.
• Negate tests with NOT. No AND or OR operators available.

Script Parameters

• Access with %0, %1, %2, etc.
• Use shift to manipulate parameter list.

Looping

• Use FOR to iterate over files or parameters.
• EnableDelayedExpansion allows variable updates within loops.

Loop through a List of Files or Parameters

• Iterate over filenames, patterns, strings, or parameters.

Example of Looping

• Example loops through file deletion choice and integer counting.

Examples

• Integer vs String comparisons.
• Coin flip example using random integer.