Lecture 3. Unix. Question? b. The world s best restaurant. c. Being in the top three happiest countries in the world.

Transcription

1 Lecture 3 Unix 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.

2 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)

3 OS Computers are closed boxes, hiding the command line and lower level features. rm what s? vs. OS The Operating System is a resource manager. Many different types of operating system, e.g. Windows, OSX, Unix/Linux.

4 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.

5 Unix-history Incarnations? Berkeley Software Distribution (BSD) Solaris (Sun) Linux - a free open source UNIX OS originally developed by Linus Torvalds in Mac OSX - based on BSD, (Berkeley Software Distribution) version of Unix.

6 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.

7 Limitations of Unix? Too many choices for distributions (Linux). Lacks some widely used software (e.g. Photoshop). Architecture Applications Shell Kernel Hardware

8 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.

9 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.

10 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.

11 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

12 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 a directory owner group date and time last modified $ ls -la total 72 drwxr-xr-x 9 mwirth staff Sep 11:25. drwxr-xr-x@ 272 mwirth staff Sep 11:04.. -rwxr-xr-x 1 mwirth staff Sep 10:06 a.out -rw-r--r--@ 1 mwirth staff Jul 18:48 gamepig.c -rwxrwxrwx@ 1 mwirth staff Jun 10:02 luhn.c -rw-r--r--@ 1 mwirth staff Jul 12:01 mugwump.c -rw-r--r--@ 1 mwirth staff Aug 08:04 paragraph.txt -rw-r--r-- 1 mwirth staff Aug 08:36 paragraph2.txt -rw-r--r--@ 1 mwirth staff Jul 10:06 scramble.c $ permissions no. bytes file name

13 ls current directory $ ls -la total 72 drwxr-xr-x 9 mwirth staff Sep 11:25. drwxr-xr-x@ 272 mwirth staff Sep 11:04.. -rwxr-xr-x 1 mwirth staff Sep 10:06 a.out -rw-r--r--@ 1 mwirth staff Jul 18:48 gamepig.c -rwxrwxrwx@ 1 mwirth staff Jun 10:02 luhn.c -rw-r--r--@ 1 mwirth staff Jul 12:01 mugwump.c parent directory -rw-r--r--@ 1 mwirth staff Aug 08:04 paragraph.txt -rw-r--r-- 1 mwirth staff Aug 08:36 paragraph2.txt -rw-r--r--@ 1 mwirth staff Jul 10:06 scramble.c $ pwd pwd is a command used to tell you which directory you are currently in.

14 cd cd is used to change directories. The general form of the cd command is as follows: cd directory-name pwd & cd current directory $ pwd /Users/mwirth/codingC $ cd afall15 change directory to afall15 $ ls a.out!! luhn.c!! paragraph.txt! scramble.c gamepig.c! mugwump.c! paragraph2.txt $ cd.. $ change directory to the parent (codingc)

15 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

16 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

17 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

18 rm rm is used to delete files. The general form of the rm command is as follows: rm filename rm CAREFUL!! rm is forever.

19 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

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

21 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.

22 history Commands in the list can be accessed and reexecuted 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 $ $!505 gcc scramble.c $ $!g gcc scramble.c $

23 Redirecting output stdout mean the standard standard output (screen). It is also possible to redirect this using the operator >. Redirecting output $ ls a.out!! luhn.c!! paragraph.txt! scramble.c gamepig.c! mugwump.c! paragraph2.txt $ $ ls > flist $ Instead of outputting to the screen this redirects it to a file named flist.

24 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 $ history grep cd 352 cd PRAC_inprog/ 383 cd codingc 501 cd codingc 503 cd afall15/ 545 cd history grep cd $ Pipes Run the history command, then pipe the results into grep which will return all lines which contain the search term cd.

25 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: bash ttys001 0: 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: bash ttys001 0: bash

26 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:

27 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: bash ttys000 0:00.12./a.out ttys001 0: bash $ kill $ Need more info? Use man. Short for manual page. The general form of a man page is as follows: man command-name

28 Unix is all powerful You can write programs in shell languages, to perform processing that is easier than using a GUI. For example: #!/bin/bash for img in *.jpg do filename=$(basename "$img") extension="${filename##*.}" filename="${filename%.*}" echo $filename convert "$img" "$filename.png" done Shell scripting Use the bash shell Select all files ending in.jpg #!/bin/bash for img in *.jpg do filename=$(basename "$img") extension="${filename##*.}" } filename="${filename%.*}" echo $filename convert "$img" "$filename.png" done extract file name with no extension Convert the file to.png

29 Black holes Unix has an built-in black hole called /dev/null Any user can write to it. Anything written to it just disappears.