UNIX Hints and Tips (Command Line Interface) for Beginners

Useful commands

This is a list of commands often mentioned in classes such as CS1, plus a few other useful ones. For complete information about any command, read its man page (see the description of the man command below).

Format for command descriptions

Typewriter font (like this) denotes text you should type exactly as shown,
italics (like this) denotes something you should supply (e.g., a filename), and
square brackets (like these []) enclose optional text.

In typing a command, do not include the square brackets used to denote optional text.

Commands

man commandname
Displays the "man page" for command commandname. A command's man page describes all its options and arguments. Use this to display additional options or arguments for the commands listed here. The information is displayed using the less command; see the description below for some basics on how to work with this command.
For some commands additional or alternative documentation is provided via the command info. (Why are there two? "Historical reasons" probably.) Type info info for more information about this command.
apropos keyword
Displays a list of commands related to keyword. The list is presented using the less command.
less file
Displays file (or output of another program) in a pageable/searchable form. Some things you can do:
- Type q to quit.
- Type h for help.
- Type carriage return to page forward.
- Type b to page backward.
- Type / searchstring to search for searchstring.
ls [ -l -A ] [ names ]
Displays information about names (which can be names of files or directories), or all files in the current directory if this option is omitted.
For files, information about the file is displayed; for directories, information about its contents (directories) is displayed. Normally "hidden" files or directories (those whose names start with ".") are not shown, but you can include them with -A.
If you include -l, more information is printed for each file, including the date of last modification.
cp [ -i ] fromfile tofile
Copies fromfile to tofile. If you add the -i flag and tofile exists, you will be asked whether you want to overwrite it. (Without this flag, cp silently overwrites.)
mv [ -i ] fromfile tofile
Moves (renames) fromfile to tofile. If you add the -i flag and tofile exists, you will be asked whether you want to overwrite it. (Without this flag, mv silently overwrites.)
mv [ -i ] fromfile dir
Moves fromfile to directory dir. (I.e., after execution, directory dir contains fromfile.) If you add the -i flag and dir already contains a file named fromfile exists, you will be asked whether you want to overwrite it. You can replace fromfile with an expression containing wildcards to move multiple files.
rm [ -i ] file
Removes (deletes) file. You can replace file with an expression containing wildcards to remove multiple files. If you add the -i flag, you will be asked for each file whether you really want to delete it. Warning: Once a file has been rm'd, it is basically impossible to retrieve, unless a backup has been made. Be careful!
mkdir dir
Creates a directory (folder) named dir within the current directory.
rmdir dir
Removes directory dir. Note that the directory must be empty. If it is not, you can use the following command to delete the directory and all its contents (but be sure that's what you want to do!):
rm -r dir
cd dir
Changes the current directory to dir. Some useful special cases:
- cd changes to your "home directory" (the root directory for all your files).
- cd .. changes to the parent of the current directory.
pwd
Displays the current directory.
Other tips and useful shortcuts

Interrupting programs
Most UNIX programs can be interrupted by typing control-C.
Redirecting input and output
Many programming languages have an idea of "standard input" and "standard output". By default, reading from standard input means reading what is typed in at the keyboard, and writing to standard output means printing to the screen. But UNIX allows you to "redirect" both input and output, e.g., to read standard input from a file and/or write standard output to a file.
- To have program mypgm read from file inputfile rather than from the keyboard, "redirect its input" using this command:
```
	mypgm < inputfile
	
```
- To have program mypgm write to file outputfile rather than from the keyboard, "redirect its output" using this command:
```
	mypgm > outputfile
	
```
- You can redirect both input and output, for example with this command:
```
	mypgm < inputfile > outputfile
	
```
Input redirection can be useful in program testing (so you don't have to type in your test data over and over). Output redirection can be useful in capturing program output for later use.
Command-line shortcuts
(Note that these assume that your account uses the default command shell, which it will unless you've taken steps to change it.)
- To clear the command line (e.g., if you've started typing and completely made a mess), type control-U.
- To repeat the same command you just typed, type !!. Depending on how your environment is set up, it will probably be possible to repeat other previously-typed commands as well. Typing the up arrow at the command prompt should put the previous command on the command line, with the cursor at the end. Typing another up arrow will then get the command before that, and so forth. (The down arrow cycle back through the commands in the other order.) At any time, you can press ENTER to repeat the command, use the arrow keys and backspace to edit it, or control-U to clear the line.
- When you're typing a filename, if you've typed enough of the name to uniquely determine it, if you press the TAB key the shell should fill in the rest of the name. If there are several files starting with the characters you typed in, the shell will fill in as much as it can and then beep and wait for you to type some more.
  Example: ls produces the following output:
```
	        program1.c
	        program2.c
		another_program.c
	
```
  To edit another_program.c, you can type vi an and then press the TAB key. The shell should fill in the rest of the file name another_program.c on the command line; you can then press ENTER to execute the command. To edit one of the other C files, you might type vi p and press the TAB key. The shell should then fill in as much of the name as it can and beep. You will see
```
		vi program
	
```
  on the command line. You can then enter the rest of the name (1.c or 2.c) and press ENTER to execute the command. (Or you can just type the 1 or 2 and press TAB again to let the shell fill in the rest of the name.)
Customizing your environment
UNIX permits you to customize your environment extensively. The following assumes that you have started with the default setup on the CS lab machines.
Adding command aliases
You can add aliases (short names) for commands you use frequently by modifying the file .bashrc in your home directory. You can even redefine existing commands. For example, inserting the following lines:
```
alias cp='cp -i'
alias mv='mv -i'
alias rmi='rm -i'
alias l='ls -Al'
```
redefines the cp and mv commands to always use the -i option, and defines new commands rmi (rm with the -i option) and l (ls with options -Al). (Note that ls -Al is the same as ls -A -l.)
File security
By default the files you create on the lab machines should be readable and writable only by you. File security and how to control it is briefly described in J. Oldham's tutorial on UNIX file security. A way to check that no one else can access your files is to have a friend try; if the result is the message Permission denied, all is well.

UNIX Hints and Tips (Command Line Interface) for Beginners

Useful commands

Format for command descriptions

Commands

Other tips and useful shortcuts

Interrupting programs

Redirecting input and output

Command-line shortcuts

Customizing your environment

Adding command aliases

File security