23. Check that hello.txt now contains (substitute your info for mine): hello rcwhaley: Dr. Whaley

Transcription

1 Assignment 0: Basic Unix Exploration Due: Wednesday 01/15/2018 (before class) In this assignment, you will become familiar with a few tools required to work in the Unix environment. Take your time, and try to understand each step as fully as possible, since its purpose is for you to learn how to use the programming environment used in the class. There is no need to finish it one sitting. To do this work, you will need to log into the Linux machines at burrow.soic.indiana.edu. All common OSes have methods of getting remote terminal access: Linux/OS X: use ssh. Open up a terminal window, and type: ssh -X username@burrow.soic.indiana.edu Windows: install and use PuTTY from the course website. In doing the following, I will tell you what to do and the command to do it. You need to understand what you are doing and remember the command since I will only tell you once. I also suggest that you read about these commands in your book, or on the web (via the main page links and/or googling them), or by reading the Unix man page via the man command. The man page gives relatively complete information, and are written in a bit intimidating style, which you will become used to over time. Directory heirarchy operations: 1. Log in as outlined above 2. After logging in, check what your current directory is by using pwd (print working directory). After login, your working directory should be your home directory, which in my case is: /nfs/nfs6/home/rcwhaley. The output of pwd is the full path to your home directory. 3. Create a subdirectory (AKA a folder) under your home directory with the command mkdir courses 4. Read about the mkdir command with man mkdir 5. Create a subdirectory called oops. 6. Look at all the files/directories in your current directory with the command ls -CF. Do you see the courses & oops subdirectories that you created above? Execute ls -l to see more information on the files/directories in your home directory. Read a little of the man page to see what information this command is telling you. 7. Delete the directory oops using the command rmdir oops. Read the man page for rmdir. 8. Change directories to your courses subdirectory with the command cd courses. Note that if you type the first several letters of a file or directory, and then hit tab, your shell can auto-type the rest of the filename for you! 9. Make the directory ISE under your courses directory. 10. Change directories to your ISE directory. 11. Make the directory 111 under your ISE directory. 12. Change directories to your 111 directory. 1

2 13. Change to your home directory using cd. Notice that a cd with no arguments changes to your home directory. The tilde (~) is shorthand for your home directory, so instead of referring to my courses directory as /nsf/nsf6/home/rcwhaley/courses I can use ~/courses. 14. Make an alias, cd111, to change directories to your newly created 111 directory with the command: alias cd111="cd ~/courses/ise/111" Thus, when you type cd111 it will be replaced by the shell with the cd command on the right. Notice that this only works in the shell in which the alias was executed (i.e., if you open up a second terminal window, or log out of this one, then you must create the alias again to be able to use it). 15. Change to your 111 directory with cd111, verify that you are there with pwd. 16. Create a subdirectory of 111 called asg Change to your home directory and make a subdirectory tmp where you can play with stuff that you will delete later. 18. Change directories back to your cd asg0 19. Create a file containing the word hello using the echo command along with redirection: echo "hello" > hello.txt 20. Display the contents of the created textfile one line at a time using the cat command: cat hello.txt 21. Read the man page on cat. 22. Now, let s add a line to hello.txt that maps your user name to your real name. Issue: echo "login: my_name" >> hello.txt Make sure you replace login with your login name (as shown in your path), and my name with your actual name. For instance, I would put: echo "rcwhaley: Dr. Whaley" >> hello.txt 23. Check that hello.txt now contains (substitute your info for mine): hello rcwhaley: Dr. Whaley 24. Change back to your home directory, and create a tarfile (like a zip file) of all directories and files you have created using: tar cvf courses.tar courses 25. If you are masochistic, horrify yourself by attempting to understand the man page on tar. 26. Move this file into your asg0 subdirectory: mv courses.tar courses/ise/111/asg0/.. When doing file operations, your shell (the program running in the terminal taking things you type and executing them for you) interprets the period in this statement to mean use the same filename it had in the other directory. 27. Change to your asg0 subdirectory. 28. Scope the size of the files using ls -l 29. Compress the tarfile using: bzip2 courses.tar 2

3 30. Scope the bzip2 manpage 31. Scope the size of the files now: courses.tar will now be smaller and be called courses.tar.bz2 32. Change directory to the tmp subdirectory under your home. 33. Untar your entire courses tree structure under /tmp using: bunzip2 -c ~/courses/ise/111/asg0/courses.tar.bz2 tar xvf Verify your courses directories and files are duplicated under tmp. 35. Delete only your hello.txt from tmp by issuing: rm courses/ise/111/asg0/hello.txt 36. Verify that that hello.txt is no longer there. 37. Delete everything in tmp, and all subdirectories under it, by using (the very dangerous!) recursive rm command: rm -rf ~/tmp 38. Scope the rm manpage. If you add the -rf argument, it will recursively delete all subdirectories without verifying that that is what you meant to do, so uh, be careful with that. 39. Submit your tarfile using canvas. Editing with vim If you work in systems, you will spend a huge amount of time editing various text files. Because of this, all Unix/Linux systems come with a variety of editors. Noobs will use simple editors like pico, which are easy to run, and have almost no power (like wordpad). When you edit files for a living, however, it is much better to use a much more powerful text editor. Historically, this has meant you either learn EMACS or vi. EMACS is for people who want to get a foot pedal to run control the key, or who are hoping to get carpal tunnel early. EMACS is what you get if your design philosophy is basically: swiss army knives really need features like a toupee comb, microwave, sat phone, and clothes washer/dryer added to them. vi is for those who like a tool that punches you in the face for an entire semester, before becoming the most powerful, natural, and easy on the the typing hands editing tool ever invented. It embodies the philosophy: a knife should cut through hardened steel effortlessly, have no safety features, and that s all it should do. You may use any editor you want, but I will only answer questions on vim, which is a modern version of vi. To get started on the face-punching phase: 1. Change to the ~/tmp directory, execute vimtutor and follow the directions in order to get an introduction to the vi editor (vim is one of the fanciest modern variants of Unix s original vi editor). 3

4 Compiling, executing, and debugging C programs: 1. Back in your asg0 subdirectory, type in the following C program into the file sumfile.c (vim sumfile.c if your face is holding up): Comments (started with and ended with ) are optional, and can be changed or ommitted without changing the program. * Typed in by <YOUR NAME> for asg0 E111 #include <stdio.h> #include <stdlib.h> #include <assert.h> int main(int argc, char *argv[]) all C programs must have main char *inf; variable FILE *fpin;... int tot; declarations char *GetFlags(int argc, char **argv); function int sumfile(file *fpin); protoypes inf = GetFlags(argc, argv); fpin = fopen(inf, "r"); assert(fpin); tot = sumfile(fpin); fclose(fpin); printf("total = %d\n", tot); return(0); 0 means normal (non-error) exit * Print usage and help info when commandline args are malformed, then exit void PrintUsage(char *name, int ierr, char *flag) if (ierr > 0) fprintf(stderr, "Bad argument #%d: %s \n", ierr, flag?flag:"out-of-arguments"); else if (ierr < 0) fprintf(stderr, "ERROR: %s\n", flag); fprintf(stderr, "USAGE: %s [flags]:\n", name); fprintf(stderr, " -i <input file>\n"); * Signal abnormal termination if (ierr!= 0) exit(ierr); else exit(-1); * This routine parses the commandline arguments provided to the routine 4

5 * in order to find out what file to read in. If no file is provided, take * the default name "num.dat" * RETURNS: file name to read numbers from char *GetFlags(int argc, char *argv[]) char *infile = "num.dat"; int i; * Loop over all commandline arguments, and parse those that make sense. If * a flag is unknown or badly formed, print usage information and abort * program execution while returning an error code. * NOTE: we don t parse argv[0] since that is the name of the program, * not a flag! for (i=1; i < argc; i++) * All flags must begin with -, or they are malformed. Notice we don t * have to prototype PrintUsage, since we put PrintUsage in the file first, * and so the routine definition serves as the prototype for following * invocations. This is more fragile than prototyping, since it depends * on routines appearing in a fixed order in the source. * NOTE: PrintUsage is never returned from since it calls exit() if (argv[i][0]!= - ) PrintUsage(argv[0], i, argv[i]); switch(argv[i][1]) only i legal value for this prog! case i : -i <input file name> if (++i >= argc) do we have required following arg? PrintUsage(argv[0], i-1, NULL); infile = argv[i]; break; default: any other flag is unknown! PrintUsage(argv[0], i, argv[i]); return(infile); * This routine reads all available integers from the open file fpin, * and returns the sum of all read-in integers int sumfile(file *fpin) int num, sum=0; while ( fscanf(fpin, "%d", &num) == 1 ) sum += num; return(sum); 5

6 2. Compile the program in sumfile.c calling the executable xsum, using the command: gcc -Wall -Wpedantic -ansi -g -o xsum sumfile.c This will compile the C file, create an object file and then link this object code to the C libraries all in one step to create the executable. The object code file will not be written to the user s directory in this case. Note that we could separate the compile and link steps by: (a) gcc -Wall -Wpedantic -ansi -g -c sumfile.c (compile sumfile.c to object file, stored as sumfile.o). (b) gcc -ansi -g -o xsum sumfile.o (link object file with system libs to create executable). In this case, sumfile.o will persist in user s directory until deleted manually. If our program is spread over multiple files, just repeat step-a for each file, and then list all files during step-b. 3. Create the file num.dat with numbers totalling 30 using the command: echo -e "1 2 3\n7 8 9" > num.dat 4. Check the contents of the file by: cat num.dat 5. Have your program add up the numbers by:./xsum -i num.dat 6. Run program on invalid data with:./xsum -i noexist.dat 7. Understand what assert is doing from this response, putting additional print statements in to aid understanding if necessary. 8. Understand why this works:./xsum -i noexist.dat -i num.dat 9. valgrind is an extremely useful program that looks for memory allocation errors. You should run valgrind on all your codes that do any kind of memory allocation. To do this, simply: valgrind --leak-check=yes --malloc-fill=0x88 --track-origins=yes./xsum -i num.dat 10. To avoid typing all that, use an alias like: alias vg=valgrind --leak-check=yes --malloc-fill=0x88 --track-origins=yes 11. Here is an step that will only work if you log in from OS X/Linux using ssh -X, if you are running Linux locally, or if you use PuTTY and Xming on Windows: Compile the program and follow its execution in the debugger: (a) The -g flag tells the compiler to include debugging info in the resulting object or executable file. If you are not debugging, you can substitute the -O (Optimize) flag for -g. (b) Start running under the graphical debugger using the command: ddd./xsum (c) You will see the ddd screen and in the source windows you will see your program. You can set a breakpoint (a place to stop execution) anywhere in the program by simply right clicking its line and choosing the break button. You can also issue this command manually in the command window by typing break <routine name> (eg., break main). (d) Begin execution by typing run followed by the arguments in the command window (eg., run -i num.dat). (e) Once you reach your breakpoint, use the next and step buttons/commands to watch the program execute. Notice you can see the value of variables by hovering over them with the mouse, or using the print command. 6

7 (f) Now set a breakpoint on the line: total += num; in the loop by clicking on the line and then the break button. You should see a little red stop sign appear to the left of the line. (g) Any time that ddd has control (at a breakpoint, etc.), you can look at any of the variable values. So to see the current value of num, click on the variable in the program window, anywhere in the code, and then click the print button (or type print num in the command window). You will see the value printed in the command window. Look at the value of total: is it what you expected? (h) Click on the Cont button and execution will continue until the next loop iteration. Again look at num and total and ask if they have the expected values. Continue until program exit. (i) Now clear the break point inside the loop by clicking on the line and then clicking the Clear button. (j) To look at variable values, we need to pause and specifically print them out. It is simpler if we can just watch them change (assuming their aren t many variables). We can do this in the following way: i. Click on the dropdown menu, View, this shows various subwindows that are currently displayed. Click on Data Window. You will see a new subwindow on the top of your ddd display. ii. Type break sumfile to stop execution in the sumfile function. iii. type run (or hit the Run button) iv. Click on num in the code and then click the display tool button. num will appear in the data window with its present value, which is currently garbage since num has not yet been initialized. Do the same for total, make sure the data window is large enough for both to be seen (you an drag them to be side-by-side if you want). v. Now watch values change as you use Step to step through the execution.? When ddd stops at a break point, has the statement at the break point already executed or is it the next statement to be executed? play with debugger until you can use it well, setup your defaults to suit your style, etc. 12. Submit your sumfile.c using canvas. It is OK if it has no comments, except your name at top. 7