WHY LEARN THIS STUFF
There are several reasons why the ideas below are useful:
- Some programs only run on the command line (e.g., many latex related programs)
- Some features of programs only run on the command line
- Command line arguments can be put into batch files which can make repetitive tasks more efficient
- Understanding how the command line works helps to diagnose problems and configure software, particularly when setting up multiple programs that are designed to work together (e.g., TeXnicCenter with latex or pdftex; Eclipse with R; etc.)
RUNNING COMMANDSThere are many ways to run programs that make use of the concepts of the command line. The following discusses some common scenarios in Windows.
Command Line: The command line can be opened by typing Windows+R, cmd, [ENTER]
A useful tool is the Open Command Window Here in the Windows Power Tools. It allows you right click a folder in Windows Explorer and open the command prompt with the same current directory.
Typing: help brings up the standard list of commands. I learnt the basic commands years ago and they do come in handy from time to time. While you probably already know these commands, if you don't (perhaps you've grown up in a Post-Dos Windowed world), the following are perhaps the most important for getting started:
- cd (changing directory)
- dir (for listing files in a directory)
- the basics of wild card characters e.g., *.txt to list all txt files
- md (make a directory)
- copy (copying files)
- xcopy (copying directories and subdirectories - good for backup, although I prefer xxcopy)
- del: (delete files)
Also, see this discussion on StackOverflow regarding PowerShell and CygWin.
Run: Type Windows+R
Windows Shortcuts: Optional arguments can be given to a program to make it open in a different way. These optional arguments can be recorded in Shortcuts such that opening the shortcut loads the programs with the options activated.
For example, Create a new shortcut and specify the target as follows:
"C:\Program Files\R\R-2.9.1\bin\Rgui.exe" --internet2
This will open R (at least on my system) using a proxy server for internet connectivity.
Batch files: Batch files are text files with a *.bat extension used to run commands on windows. Here's an introductory tutorial. One easy way to run command line programs on a file is to create a batch file in the directory, type the command into the batch file (right click - edit), and then run the command.
From an External Program: Some programs facilitate the running of external programs. Such features are most commonly found in text editors designed for programming. For example, TeXnicCenter allows for output profiles (see more info below).
AutoHotKey (Also see AutoIt): AutoHotKey is a program that allows for the creation of scripts to automate various tasks. It can also be used to set up shortcut keys. You could use it to run command line programs such as batch files. Or you can write elements of a batch file directly into the script.
Programs and files are stored in particular directories. In order for a program to run, Windows needs to be able to find it. Thus, if you wanted to run "latex" by typing "latex" in the command line, "latex" would need to be located somewhere in the path.
A file can be found because:
- The file name is given and it is in the working directory
- The file name is given and the directory that it is located in is specified in the "path" environment variable
- A relative directory and file name is given and the file is relative to the working directory
- An absolute directory and file name is given
- In some instances variables are used to denote some aspect of the path (e.g., for program files, system directory, and so on)
When adventuring into the world of open source software a failure to have your path variable set correctly is a common cause of problems. Victor Laurie lists some of the Environment Variables that can be used in paths on Windows and also explains how to edit the path.
COMMANDS AND ARGUMENTS
Many programs have command line options. These options alter the behaviour of the program.
Learning about command line arguments
If you are new to a program, you may want to learn about the command line options that are available. The following are some common ways of obtaining help.
- At the command prompt type: help [program] ; e.g., help cd ; This tends to work with Windows commands.
- At the command prompt type: [program]/? ; e.g., cd/?; This tends to work with Windows commands
- At the command prompt type: [program] --help ; e.g., R -- help ; or latex --help ; This tends to work with programs coming from the Linux world.
- If the program has a GUI, open the GUI and go to the help menu.
- Do a search on Google with search terms: [ProgramName] and "command line" and perhaps a word like "options", "switches", or "arguments": e.g., for Jabref, latex, MS Word
The help should specify the order of arguments and whether arguments are optional or required.
Options are often prefaced by a special character such as "-", "--", or "/". For example, rgui --vanilla starts R in Windows with a particular set of options; or cd /d d: changes the working directory to "d:" and the "/d" switch permits a change of drive. Some are specified using attribute=value syntax (e.g., latex -interaction=nonstopmode ... specifies a particular mode of interaction in LaTeX).
Files, folders, and other arguments that contain spaces require particular care. They often need to be enclosed in quotation marks.
VARIABLESSome programs also provide variables such that when you run the program the variables are replaced with their current value. These typically follow a special syntax and often start with a special character (e.g., %). This is used extensively with programming text editors to integrate files within the editor with external programs such as compilers.