Lecture 3Unix

Question?

• Denmark is famous for?

a. LEGO.

b. The world’s best restaurant.

c. Being in the top three happiest countries in the world.

d. Having the highest taxes in Europe (57%).

e. All of the above.

Announcements

• There are drop-in help sessions in Reynolds 001/002 (right after lectures).

• There are TAs who are dedicated just to private tutoring sessions.  The tutoring times can be booked from the course website and are free to the students.  

• There are times available beginning next week and anyone who is feeling even a tiny bit overwhelmed should take advantage of the tutoring.  

• If the students don't use it we'll stop offering it.

Q&A

• Do you have a question?(I may have an answer)

Computers are closed boxes, hiding the command line and lower level features.

rm vs.

what’s

?

OS

OS

• The Operating System is a resource manager.

• Many different types of operating system, e.g. Windows, OSX, Unix/Linux.

Unix

Unix

• Unix is a multi-user, multi-tasking environment, offering stability, portability and powerful networking capabilities.

• Unix was created by Ken Thompson and Dennis Ritchie at AT&T in the early 1970s.

• Evolved from UNICS (Uniplexed Information and Computing System) written in assembler.

Unix-history

Incarnations?

• Berkeley Software Distribution (BSD)

• Solaris (Sun)

• Linux - a free open source UNIX OS originally developed by Linus Torvalds in 1991.

• Mac OSX - based on BSD, (Berkeley Software Distribution) version of Unix.

Importance?

• C and Unix evolved together.

• Unix kernel was re-written in C.

Benefits of Unix?

• The kernel itself is relatively small.

• Can be built specifically for the platform it runs on (OSX), or usable on anything, such as a wristwatch (Linux).

• Scales well.

• Can support fully-featured GUI, yet maintains the command-line.

Limitations of Unix?

• Too many choices for distributions (Linux).

• Lacks some widely used software (e.g. Photoshop).

Architecture

Hardware

Kernel

Shell

Applications

Kernel

• Interacts with hardware to perform memory management, task scheduling, and file management.

• Technically, the kernel “is” the OS.

Shells

• Textual command line shells.

• Processes user requests - commands are translated by the shell into something the kernel can understand.

Shells

• OSX, and many versions of Linux use the Bash shell as its default - the Bourne Again Shell.

• Many different types of shells: C shell (csh), Bourne shell (sh), Korn shell (ksh)

System utilities

• Commands such as ls, cp, grep, awk, sed, bc, wc

• Can be combined together to solve problems.

Unix file system

• Organized in a tree structure.

Unix file system

• Unix file systems have directories and files.

• Unix is CASE sensitive.

• This means Vader, vader, VADER, vaDer are all different.

Types of files

• Plaintext - files in human-readable format. e.g. readme.txt

• Binary - files in machine-code. For example executables (a.out), .zips, .pdfs, .jpgs

Commands

• A Unix command line consists of the name of a Unix command, followed by its "arguments" (options and the target filenames and/or expressions).

• The general syntax for a UNIX command is:

$ command -options targets ↵

ls

• ls is used to list files in a directory.

• By itself it just lists the file names, in alphabetical order.

• The command ls -la will list information associated with each file.

ls

$ ls -latotal 72drwxr-xr-x 9 mwirth staff 306 1 Sep 11:25 .drwxr-xr-x@ 272 mwirth staff 9248 1 Sep 11:04 ..-rwxr-xr-x 1 mwirth staff 9640 1 Sep 10:06 a.out-rw-r--r--@ 1 mwirth staff 3094 3 Jul 18:48 gamepig.c-rwxrwxrwx@ 1 mwirth staff 1439 30 Jun 10:02 luhn.c-rw-r--r--@ 1 mwirth staff 1717 3 Jul 12:01 mugwump.c-rw-r--r--@ 1 mwirth staff 490 31 Aug 08:04 paragraph.txt-rw-r--r-- 1 mwirth staff 473 31 Aug 08:36 paragraph2.txt-rw-r--r--@ 1 mwirth staff 3778 3 Jul 10:06 scramble.c$

a directory

permissions

owner group

no. bytes

date and time last modified

file name

ls

$ ls -latotal 72drwxr-xr-x 9 mwirth staff 306 1 Sep 11:25 .drwxr-xr-x@ 272 mwirth staff 9248 1 Sep 11:04 ..-rwxr-xr-x 1 mwirth staff 9640 1 Sep 10:06 a.out-rw-r--r--@ 1 mwirth staff 3094 3 Jul 18:48 gamepig.c-rwxrwxrwx@ 1 mwirth staff 1439 30 Jun 10:02 luhn.c-rw-r--r--@ 1 mwirth staff 1717 3 Jul 12:01 mugwump.c-rw-r--r--@ 1 mwirth staff 490 31 Aug 08:04 paragraph.txt-rw-r--r-- 1 mwirth staff 473 31 Aug 08:36 paragraph2.txt-rw-r--r--@ 1 mwirth staff 3778 3 Jul 10:06 scramble.c$

current directory

parent directory

pwd

• pwd is a command used to tell you which directory you are currently in.

cd

• cd is used to change directories.

• The general form of the cd command is as follows:

cd directory-name

pwd & cd

$ pwd/Users/mwirth/codingC$ cd afall15$ lsa.out! ! luhn.c! ! paragraph.txt! scramble.cgamepig.c! mugwump.c! paragraph2.txt$ cd ..$

change directory to afall15

change directory to the parent (codingC)

current directory

cp

• cp is used to make copies of files.

• The general form of the cp command is as follows:

cp srcFile destFile

cp

• cp can also be used to put a copy of a file into a directory.

• The general form of this cp command is as follows:

cp srcFile destDir

cp

• To copy the file a1Mug.c to a1MugBACKUP.c :

cp a1Mug.c a1MugBACKUP.c

• To copy the file a1Mug.c to a directory named a1BACKUPs :

cp a1Mug.c a1BACKUPS

mv

• mv is used to rename files.

• The general form of the mv command is as follows:

mv srcFile destFile

mv

• mv can also be used to move a file into a directory (this does not make a copy).

• The general form of this mv command is as follows:

mv srcFile destDir

cp

• To rename the file a1Mug.c to a1Mug.old :

mv a1Mug.c a1Mug.old

• To move the file a1Mug.c to a directory named deathStarPlans :

mv a1Mug.c deathStarPlans

rm

• rm is used to delete files.

• The general form of the rm command is as follows:

rm filename

rm

CAREFUL!!

rm is forever.

Other commands

• mkdir - make a directory

• rmdir - remove a directory

• touch - create an empty file, or modify a files timestamp

• cat - concatenate files, and print to screen

• more - similar to cat, but displays one screen at a time.

grep

• The grep command searches for lines matching a specific pattern.

• The general form of the grep command is as follows:

grep pattern files

grep

$ grep main *.cgamepig.c:int main(void)luhn.c: // Return the remainder when divided by 10luhn.c:int main(void)mugwump.c:int main(void)scramble.c:int main(void)$

find

• The find utility is used to search for files in a directory hierarchy.

• The general form of the find command is as follows:

find path conditions

find

$ find . -name mugwump.c./mugwump.c$

history

• All shells store a list of the commands that have been issued.

• The command history allows you to see this list.

history

• Commands in the list can be accessed and re-executed using a single exclamation mark, !, which is often referred to as Bang.

• You can do ! followed by a history number, or ! followed by the first few characters of the command.

history

$ history 503 cd afall15/ 504 ls 505 gcc scramble.c 506 ./a.out$$ !505gcc scramble.c$$ !ggcc scramble.c$

Redirecting output

• stdout mean the standard standard output (screen).

• It is also possible to redirect this using the operator >.

Redirecting output

$ lsa.out!! luhn.c!! paragraph.txt! scramble.cgamepig.c! mugwump.c! paragraph2.txt$$ ls > flist$ Instead of outputting

to the screen this redirects it to a file

named flist.

Pipes

• The pipe creates a channel from one command to another.

• Pipes are created using the |.

• The general form of a pipe is as follows:

command1 | command2

Pipes

$ history | grep cd 352 cd PRAC_inprog/ 383 cd codingC 501 cd codingC 503 cd afall15/ 545 cd .. 568 history|grep cd$

Run the history command, then pipe the results into grep which will return all

lines which contain the search term cd.

Processes

• Everything that runs in an OS has a process.

• A process is an instance of a running program.

• The ps (process snapshot) command tells you about your processes.

$ ps PID TTY TIME CMD 9878 ttys000 0:00.32 -bash11641 ttys001 0:00.02 -bash

Processes

• Every process has a PID, or Process-ID, which identifies it.

• You can have a program running more than once... each will have their own PID.

$ ps PID TTY TIME CMD 9878 ttys000 0:00.32 -bash11641 ttys001 0:00.02 -bash

Processes

• To see everything running in the background, you can use ps -A

$ ps -A PID TTY TIME CMD 1 ?? 2:51.39 /sbin/launchd 11 ?? 0:05.62 /usr/libexec/UserEventAgent 12 ?? 0:09.27 /usr/libexec/kextd

When things go wonky...

• If a program runs for too long... maybe because it has gone into an infinite loop or something, it can be stopped by using:

When things go wonky...

• Sometimes a program will get stuck for some reason. It just stops responding.

• When this happens it’s time to kill the process.

$ ps PID TTY TIME CMD 9878 ttys000 0:00.35 -bash11769 ttys000 0:00.12 ./a.out11641 ttys001 0:00.02 -bash$ kill -9 11769$

Need more info?

• Use man.

• Short for manual page.

• The general form of a man page is as follows:

man command-name

Unix is all powerful

• You can write programs in shell languages, to perform processing that is easier than using a GUI.

• For example:#!/bin/bashfor img in *.jpgdo filename=$(basename "$img") extension="${filename##*.}" filename="${filename%.*}" echo $filename convert "$img" "$filename.png"done

Shell scripting

#!/bin/bashfor img in *.jpgdo filename=$(basename "$img") extension="${filename##*.}" filename="${filename%.*}" echo $filename convert "$img" "$filename.png"done

Use the bash shell

Select all files ending in .jpg

}extract file name with

no extension

Convert the file to .png

Black holes

• Unix has an built-in black hole called

/dev/null

• Any user can write to it.

• Anything written to it just disappears.