Help on any Unix Command

Getting help is one of the most important things you will need to take from this tutorial. At any point you wish to learn more about any single command you can use the following tools.

Example (to quit 'man' command hit the letter 'q', page down with arrow keys):

$ man ls

LS(1)                           User Commands                           LS(1)

NAME
   ls - list directory contents

SYNOPSIS
   ls [OPTION]... [FILE]...

DESCRIPTION
   List  information  about the FILEs (the current directory by default).
   Sort entries alphabetically if none of -cftuSUX nor --sort.

Terminal Window

This is where you type all these fun commands, opening a new terminal window is slightly different on each GUI platform. Here are some of the most common ones.

• Redhat (ECE Lab Machines): Applications > System Tools > Terminal
• Ubuntu: Applications > Accessories > Terminal
• MacOS: Applications > Utilities > Terminal

Change Directories

To move around the filesystem you will need to familiarize yourself with these commands. cd or change directory

Example:

$ pwd
/home/students/user/

$ cd Directory1
$ pwd
/home/students/user/Directory1/

$ cd
$ pwd
/home/students/user/

Make a New Directory

Remove a Directory

List Files

Display a list of files in your current directory or in {path}

Example:

    $ ls -laF

drwx-----x  23 user group      8192 2008-02-12 13:49 ./
drwxr-xr-x 142 user group     24576 2008-03-05 08:42 ../
-rw-r--r--   1 user group      7475 2006-12-08 13:25 afile.txt
-rw-r--r--   1 user group      3583 2007-02-02 13:07 anotherfile.txt
drwx------   3 user group      8192 2007-09-17 08:46 Directory1/
drwxr-xr-x   2 user group      4096 2006-08-17 13:04 Directory2/

Copy a File or Directory

Move/Rename a File

Example:

$ ls -F
file1
Directory/

$ mv file1 file2
$ ls -F
file1
Directory/

$ mv file2 Directory/
$ cd Directory
$ ls
file2

Delete a File

View a Text File

Edit a Text File

Create a New File

Compare two files

Other Useful Text Commands

Wildcards and Shortcuts

*

Match any string of characters, eg page* gets page1, page10, and page.txt.

?

Match any single character, eg page? gets page1 and page2, but not page10.

[...]

Match any characters in a range, eg page[1-3] gets page1, page2, and page3.

~

Short for your home directory, eg cd ~ will take you home, and rm -r ~ will destroy it.

.

The current directory.

..

One directory up the tree, eg ls ...

Pipes and Redirection

Pipes and Redirection are useful tools to chain commands together to do complex operations. They are usually for advanced users but some uses are very simple and hard to live with out.

{command} > {file}

Redirect output to a file, eg ls > list.txt writes directory to file.

{command} >> {file}

Append output to an existing file, eg cat update >> archive adds update to end of archive.

{command} < {file}

Get input from a file, eg sort < file.txt

{command} < {file1} > {file2}

Get input from file1, and write to file2, eg sort < old.txt > new.txt sorts old.txt and saves as new.txt.

{command} | {command}

Pipe one command to another, eg ls | more gets directory and sends it to more to show it one page at a time.

File Permissions

Unix permissions concern who can read a file or directory, write to it, and execute it.

• 'r' = read
• 'w' = write
• 'x' = execute (for directory or programs)

Consider one of the examples from List Files above:

$ ls -l
-rw-r--r--   1 user group      7475 2006-12-08 13:25 afile.txt
drwx------   3 user group      8192 2007-09-17 08:46 Directory1/

The permissions on this file are displayed in the first column -rw-r--r--:

-rw-r--r--
drwx------
||||||||||
||||||||||
|||||||+++--- World Permission (rwx)
||||+++-------Group Permission (rwx)
|+++----------User(owner) Permission (rwx)
+-------------File Type "d" = directory '-' = file 'l' = Symbolic link

The other columns are as follows:

1     user     group      7475   2006-12-08 13:25     afile.txt
(*)  (owner)  (group)   (size)  (last modified date) (filename)

* Number of symbolic links to this file

You can change file permissions with letters:

• 'u' = user (yourself)
• 'g' = group
• 'o' = world
• 'a' = everyone

chmod u+rw {file}

Give yourself read and write permission

chmod u+x {file}

Give yourself execute permission.

chmod a+rw {file}

Give read and write permission to everyone. (Use this with caution!)

chmod o-rwx {file}

Remove read, write and execute from world

Example:

$ ls -l afile.txt
-rw-r--r--   1 user group      7475 2006-12-08 13:25 afile.txt
$ chmod u+x afile.txt
$ ls -l afile.txt
-rwxr--r--   1 user group      7475 2006-12-08 13:25 afile.txt
$ chmod o-r afile.txt
$ ls -l afile.txt
-rwxr-----   1 user group      7475 2006-12-08 13:25 afile.txt

System Info

How to Make an Alias

An alias lets you type something simple and do something complex. It's a shorthand for a command. If you want to type "dir" instead of "ls -l" then type alias dir 'ls -l'. The single quotes tell Unix that the enclosed text is one command. The command to create an alias differs on each shell.

The ECE default shell is bash which will automatically read aliases that are in your .bash_aliases file. The tcsh shell will read the .csh_aliases file.

Example of a .bash_aliases file (bash, sh and ksh use this format):

# alias {alias name}="{command}"
alias ls="ls -F"
alias ll="ls -lah"
alias ssh="ssh -X"
alias mroe="more"
alias vi="vim"

Example of a .csh_aliases file (csh and tcsh use this format):

# alias {alias name} "{command}"
alias ll "ls -la"
alias dir "ls -la | less"
alias rm "rm -i"

How to Make a Script

A Unix script is a text file of commands that can be executed, like a .bat file in DOS. Unix contains a powerful programming language with loops and variables that I don't really understand. Here's a useful example.

Unix can't rename a bunch of files at once the way DOS can. This is a problem if you develop Web pages on a DOS machine and then upload them to your Unix Server. You might have a bunch of .htm files that you want to rename as .html files, but Unix makes you do it one by one. This is actually not a defect. (It's a feature!) Unix is just being more consistent than DOS. So make a script!

Make a text file (eg with pico) with the following lines. The first line is special. It tells Unix what program or shell should execute the script. Other # lines are comments:

#! /bin/csh
# htm2html converts *.htm files to *.html
foreach f ( *.htm )
   set base=`basename $f .htm`
   mv $f $base.html
end

Save this in your home directory as htm2html (or whatever). Then make it user-executable by typing chmod u+x htm2html. After this a * will appear by the file name when you ls -F, to show that it's executable. Change to a directory with .htm files and type ~/htm2html, and it will do its stuff.

Think about scripts whenever you find yourself doing the same tedious thing over and over.

Dotfiles (aka Hidden Files)

Dotfile names begin with a "." These files and directories don't show up when you list a directory unless you use the -a option, so they are also called hidden files. Type ls -la in your home directory to see what you have.

Some of these dotfiles are crucial. They initialize your shell and the programs you use, like autoexec.bat in DOS and .ini files in Windows. rc means "run commands". These are all text files that can be edited, but change them at your peril. Make backups first!

Here's some of what I get when I type ls -laF:

.addressbook        my email addressbook.
.cshrc              my C-shell startup info, important!
.gopherrc       my gopher setup.
.history        list of past commands.
.login              login init, important!
.lynxrc         my lynx setup for WWW.
.pinerc         my pine setup for email.
.plan               text appears when I'm fingered, ok to edit.
.profile        Korn shell startup info, important!
.project        text appears when I'm fingered, ok to edit.
.signature      my signature file for mail and news, ok to edit.
.tin/               hidden dir of my tin stuff for usenet.
.ytalkrc        my ytalk setup.

DOS vs UNIX Commands