An Introduction to the Unix Command Line

An Introduction to the Unix Command Line What is Unix? A fully featured modern operating system It is available in a variety of “flavors.” It’s comprised of simple tools that perform a single function well. These tools can be used together to perform complex tasks. Unix is Made Up of Processes • Running Programs User owned System owned Files • Regular Files: – Data – Executables <-- usually start a process • Directory Files – Contain other files and directories • Special Files Our View of the World as Users Your Shell Unix Shell A shell is a process that acts as an interface to the OS. It allows the user to run programs individually and together to accomplish a task. Use the command line While graphical user interfaces are available and often used on Unix systems you must have a working knowledge of the standard command line utilities, pipes, and I/O redirection to benefit from the considerable strengths of Unix. Simple Unix Directory Structure / usr etc home grad bin ugrad ... var ... local bin ... class mmscott jpeckhar... Your First Command Man(manual) -- Documentation is your friend • Syntax: man topic • man provides online documentation on nearly every standard command and configuration file. • Optional Syntax: man -k keyword • man man for more details Special Directories Home Directory • /home/grad/jpeckhar • ~jpeckhar • ~ • A user generally has permission to freely manipulate files within this directory and its children. • Users start with their home directory as their pwd when they login. Changing Directories • The cd(Change Directory) command is used to change directories • cd path • Paths can be relative or absolute • pwd reports present working directory • cd when entered by itself sets the pwd to the user’s home directory. Your Prompt Helps you Navigate The default prompt on your CS account tells you what directory is your pwd(where you are at the moment). Some Examples: – csy12:~/bin> – csy12:/home – csy12:/usr/man Other File System Utilities • ls • cp • mv • rm • mkdir • rmdir Lists all files in a directory Copies files Moves files Deletes files Makes directories Removes directories Basic Syntax • ls • cp • mv • rm • mkdir • rmdir ls cp source dest OR cp source … dir mv source dest OR mv source … dir rm file mkdir new directory name rmdir directory to be removed Other Simple Commands Other Comands Every Unix distribution comes with hundreds of other standard commands that can be used for everything from viewing and searching files to developing software. Look through /bin, /usr/bin, and /usr/local/bin on most systems system and look at the man pages for the programs in those directories for more information. Using Other Commands Syntax: command file • cat • grep • more • less Echos file contents to the screen Searches a file for a string Echos a file a line at a time Same as more but more features • wc • sort Counts the words in a file and more Sorts the contents of a file Pipes and Redirection The Unix “philosophy” involves a set of generic tools which each do one thing well. Using these tools together allows you to appreciate the power of the Unix command. In Unix everything (including hardware devices) is treated as a File that can be read from and written to. Pipes • Pipes connect stdout of one command to stdin of another comand. i.e. • ls | less • cat student_list | grep senior | sort I/O Redirection • I/O redirection allows the user to change where input to a command or output from a command goes to/comes from. • cat student_list > outfile • program < infile • program < infile > outfile Standard File Handles Every Unix process automatically comes with three file handles or descriptors. These are: – Standard Input (stdin) • Keyboard – Standard Output (stdout) • Display – Standard Error (stderr) • Display (unbuff) Three Default Open Files Program stdout Buffer stdin stderr Standard File Handles All standard shells provide a facility to remap these three file handles to other devices and files in addition to other commands. This allows one to use several simple Unix commands to perform a complex task. Pipes Program 1 stdout Pipe stdin Program 2 stdout Pipe stdin Program 3 Shell/Environment Variables Shell Variables Parent Process VAR=1 Environment Variables Parent Process VAR=1 Child Process VAR=???? Child Process VAR=1