Learning Unix/Linux - UCR

Learning Unix/Linux - UCR

CS 141 Labs are mandatory. Attendance will be taken in each lab. Make account on moodle. Projects will be submitted via moodle.

Connecting to a Unix/Linux system Open up a terminal: Connecting to a Unix/Linux system

Open up a terminal: The prompt The current directory (path)

The host What exactly is a shell? After logging in, Linux/Unix starts another

program called the shell The shell interprets commands the user types and manages their execution The shell communicates with the internal part of the operating system called the kernel

The most popular shells are: tcsh, csh, korn, and bash The differences are most times subtle For this tutorial, we are using bash Shell commands are CASE SENSITIVE!

Help! Whenever you need help with a command type man and the command name

Help! Help! Help!

Unix/Linux File System NOTE: Unix file names are CASE SENSITIVE!

/home/mary/ /home/john/portfolio/ The Path

Command: pwd To find your current path use pwd Command: cd

To change to a specific directory use cd Command: cd ~ is the location of your home directory

Command: cd .. is the location of the directory below current one Command: ls

To list the files in the current directory use ls Command: ls ls has many options

-l long list (displays lots of info) -t sort by modification time -S sort by size -h list file sizes in human readable format -r reverse the order

man ls for more options Options can be combined: ls -ltr Command: ls -ltr

List files by time in reverse order with long listing General Syntax: * * can be used as a wildcard in unix/linux

Command: mkdir To create a new directory use mkdir Command: rmdir To remove and empty directory use

rmdir Displaying a file Various ways to display a file in Unix cat

less head tail Command: cat

Dumps an entire file to standard output Good for displaying short, simple files Command: less less displays a file, allowing

forward/backward movement within it return scrolls forward one line, space one page y scrolls back one line, b one page use / to search for a string

Press q to quit Command: head head displays the top part of a file By default it shows the first 10 lines

-n option allows you to change that head -n50 file.txt displays the first 50 lines of file.txt Command: head

Heres an example of using head: Command: tail Same as head, but shows the last lines

File Commands Copying a file: cp Move or rename a file: mv Remove a file: rm

Command: cp To copy a file use cp Command: mv To move a file to a different location use mv

Command: mv mv can also be used to rename a file Command: rm

To remove a file use rm Command: rm To remove a file recursively: rm r Used to remove all files and directories

Be very careful, deletions are permanent in Unix/Linux File permissions Each file in Unix/Linux has an associated

permission level This allows the user to prevent others from reading/writing/executing their files or directories Use ls -l filename to find the permission

level of that file Permission levels r means read only permission w means write permission

x means execute permission In case of directory, x grants permission to list directory contents File Permissions

User (you) File Permissions

Group File Permissions The World

Command: chmod If you own the file, you can change its permissions with chmod Syntax: chmod [user/group/others/all]+[permission] [file(s)]

Below we grant execute permission to all: Command: ps To view the processes that youre running:

Command: top To view the CPU usage of all processes: Command: kill To terminate a process use kill

Input/Output Redirection (piping) Programs can output to other programs Called piping program_a | program_b

program_as output becomes program_bs input program_a > file.txt program_as output is written to a file called file.txt

program_a < input.txt program_a gets its input from a file called input.txt A few examples of piping

A few examples of piping Command: wc To count the characters, words, and lines in a file use wc

The first column in the output is lines, the second is words, and the last is characters A few examples of piping

Command: grep To search files in a directory for a specific string use grep Command: diff

To compare to files for differences use diff Try: diff /dev/null hello.txt /dev/null is a special address -- it is always empty, and anything moved there is deleted

gdb tutorial - link http://www.cs.cmu.edu/~gilpin/tutorial/ Repeated Squaring Technique

Step 1. Let y=1. Step 2. Is N odd? If so, let y=y*x. Step 3. Set N to the floor of N/2. Step 4. Is N=0? If so, stop; answer = y. Step 5. Set x=x^2 and go to Step 2.

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