A Brief Overview of Unix Brandon Bohrer

Topics What is Unix? – Quick introduction Documentation – Where to get it, how to use it Text Editors – Know the dominant Unix text editors, and their relative strengths and weaknesses. Filesystem – Learn the differences between Unix filesystems and those on other operating systems Using the Unix shell – Basic commands and shell syntax

What is Unix? Operating system first developed at Bell Labs in 1969 Based on design philosophy of simplicity and modularity Gave birth to a large family of operating systems. The most common of these (and the one used at Drexel) is GNU/Linux Free and open-source

Accessing Documentation man command ◦ Access online documentation for programs, functions, and more. info command ◦ More advanced documentation format, but not as widely used. apropos command ◦ Searches man pages for a command; helpful when you don’t know the exact name Course materials – Probably best source for basic commands Software manuals – More detailed and readable than man pages Books - Unix in a Nutshell available from Drexel Unix standards ◦ POSIX, Single Unix Specification ◦ Poor choice for everyday use, but may be helpful for portability questions.

Text Editors Vi (Visual Editor) ◦ Simple ◦ Available almost everywhere (part of Single Unix Specification) ◦ Mode-based UI takes some getting used to Emacs (Editor Macros) ◦ Lots of features (even has a vi mode) ◦ Highly extensible ◦ Uses multi-key keyboard shortcuts instead of modes Other editors : ◦ vim ◦ nano ◦ Kate ◦ And many more

Filesystem Overview File paths are delimited with forward slashes( / ) All directories are descendants of a root directory, called / Parent directory is denoted with two periods (..) Current directory is denoted with one period (.) Files are assigned permissions, which determine how they can be accessed and by whom.

Filesystem - Related Commands Directory manipulation ◦ cd change directory ◦ ls list files in directory ◦ mkdir make directory ◦ rmdir remove directory ◦ pwd print working directory File manipulation ◦ mv move file ◦ cp copy file ◦ rm remove file ◦ touch make file / update file timestamp

More common commands Search ◦ grep search text (General Regular Expression Parser) ◦ find search for file by name Display ◦ cat concatenate file to output ◦ echo output a given string Misc ◦ wc word/line count ◦ tail return the end of a file ◦ cmp compare files, show first difference ◦ diff compare files, show all differences ◦ ps show running processes ◦ less/more make large outputs easy to read And many more

Important Directories / Root directory /home Personal files /usr User software files /bin Executables /sbin Restricted Executables /dev Devices /usr/man Manuals /usr/src Source code /lib Important libraries /tmp Temporary, deleted on boot For full list, see Filesystem Hierarchy Standard:

File permissions Three sets of permissions ◦ Owner: Generally the file’s creator, but can be changed with chown ◦ Group: A group of users with a special set of permissions  Defined in /etc/passwd and /etc/group  File’s group is changed with chgrp ◦ Other: All other users Three flags in each set ◦ Read, write, execute ◦ Set with chmod Often encoded with each set represented by an octal digit, and each permission flag stored in a single bit ◦ E.g “Read and execute” encoded as 5 ( 2^2 + 2^0) ◦ E.g All permissions for all users encoded as 777

Shell Pipes and Metacharacters Pipes help programs work together. Use | to send output from one program to input for another. ◦ Example: cat file.txt | grep “hello” prints lines of file.txt containing the string “hello” Use > to write output to a file ◦ Example: ls > file.txt writes a directory listing to file.txt Use < to send a file to a program’s input ◦ Example: cat < file.txt prints file.txt * expands to all filenames in the current directory ◦ Example: rm./* deletes all files in current directory. ◦ Use carefully:  Easy to type rm /* and destroy the filesystem.  Use rm –i to avoid accidental deletions. See course notes or sh manual for more shell syntax.

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