Lab #12: Shell Scripting

Transcription

1 Lab #12 Page 1 of 11 Lab #12: Shell Scripting Students will familiarize themselves with UNIX shell scripting using basic commands to manipulate the le system. Part A Instructions: This part will be demonstrated in class. 1. From the Terminal window, open up a text editor with the lename on the command line: gedit myls & 2. Enter the correct required rst line into the text editor. All programming will be done in the text editor window; all testing will be done from the terminal window: #! /bin/bash 3. Save the le and, from the same terminal window from steps 2 and 3, add execute permission to it: chmod +x myls You only have to do this once. 4. The purpose of this part of the lab is to write a script called 'myls' that will perform some things that the ls command does - but without actually using the /bin/ls command (i.e., pretend that ls no longer works or exists.) Start by making myls display (the names of) all les in the present directory. Some hints: i. The echo command is used to display text in the terminal window. ii. The wildcard character * is used to represent all (non-hidden) lenames. iii. The present directory is the one that the script was started in (i.e., the c.w.d.), and does not have to be included in the command.

2 Lab #12 Page 2 of Next, make the script display all lenames in a different (hard-coded) directory. You have to add a cd command. 6. Now, enhance the script so that it will display * beside each executable le in the directory, and d beside directories. It should also display the read/write permissions as r and w (if you have them if not, it should just display a instead.) More hints: i. Use the -n switch for echo so that you can build the line of output one piece at a time. ii. Use if... else statements to output either a letter or a -. iii. Use le tests... see the manual page for the test command. (But you do not have to use the test command, just the le tests inside the square brackets of an if statement. iv. Wrap the code inside a for loop and test the for loop variable inside each if statement. 7. Finally, to make your myls that much more professional looking, modify it so that it will take the directory as a command line argument, rather than an interactive prompt. In other words, you should be able to run it as:./myls /usr/local (if the script s execute permission is set) OR bash myls /usr/local (if not) Still more hints: i. The directory on the command line is represented by the $1 variable. ii. If you want to support multiple directories on the command line, like the real ls command, you can use a for loop over all the arguments, represented by the $* variable.

3 Lab #12 Page 3 of your completed myls script to your instructor. Use 'Lab 12 myls' as the Subject. Or post on Blackboard. This part is worth 12.5% of the lab. Part B Instructions: The purpose of this lab is to write a useful, complex UNIX shell script for Linux. We will start with a skeleton shell script and add code to produce a full-featured suite of tools. CREATING AND RUNNING A SHELL SCRIPT Start two Terminal windows. One window will be used to test your shell scripts; the other to view manual pages. Start a text editor. The editor will be used to create and edit your shell scripts. Type the following example into your editor. Save the le as skel. At each line marked save your shell script and run it, either with bash skel or with chmod +x skel (you only have to run this command once) and./skel. Experiment with -x, set -x, set +x, pause, and passing various command line parameters to see what the shell script is doing at each stage. See the Examples section for command lines to try out. #! /bin/bash # # CTEC1863/2016F Shell Programming Assignment # myrm #

4 Lab #12 Page 4 of 11 # function to pause pause( ) { echo -n Press Enter to continue read junk } # variable for "recycling bin" directory RecycleBin="${HOME}/.Recycled" echo Files will be deleted in $RecycleBin # function to display program usage usage( ) { status=${1-0} echo "usage: $0" '[-i] [--] lename [...]' echo " $0 -c" } exit $status # check for the minimum number of arguments if [ $# -lt 1 ] usage 1

5 Lab #12 Page 5 of 11 # set switches to default mode (off) interactive_mode=0 # parse the command line arguments while [ "$1"!= "" ] do case "$1" in -i) interactive_mode=1 echo "set interactive mode ($interactive_mode)" ;; --) shift # skip -- break ;; -*) echo "unknown switch '$1'" usage 2 ;; *) break # this is a le: no more switches ;; esac done shift # make sure at least one lename has been passed if [ "$1" == "" ] usage 3

6 Lab #12 Page 6 of 11 # function to get user conrmation (interactive mode) conrm( ) { echo -n $* '[y/n]? ' read conrmation junk conrmation=`echo $conrmation cut -c 1` if [ "$conrmation" == "y" -o \ "$conrmation" == "Y" ] conrmed=1 else conrmed=0 } # start processing the les for f in $* do echo $f done exit 0

7 Lab #12 Page 7 of 11 Next, put this if statement before the echo $f in the for loop: if [ "$f" == "." -o "$f" == ".." ] echo "can't delete current or parent directories" Next, add this if statement after the previous if statement, but before the echo $f: if [ $interactive_mode -eq 1 ] conrm remove $f else conrmed=1 Finally, replace the echo $f with the following code: if [ $conrmed -eq 1 ] echo mv "${f}" "${RecycleBin}"

8 Lab #12 Page 8 of 11 Examples (test cases). For all examples below, somele and someotherle are the names of les that may or may not exist, somedir and someotherdir are the names of directories that may or may not exist../skel./skel -i./skel -q./skel -h./skel./skel -- --help./skel -- -i./skel -- -q./skel somele./skel somele someotherle./skel somedir./skel somedir someotherdir./skel somele somedir./skel somedir somele./skel -i somele./skel -i somele someotherle./skel -i somedir./skel -i somedir someotherdir./skel -i somele somedir./skel -i somedir somele./skel -q somele./skel * To create a le called 'somele', use the touch command: touch somele To create a directory called 'somedir', use the mkdir command: mkdir somedir

9 Lab #12 Page 9 of 11 This part is worth 12.5% of the lab. Use the script command to verify that you have completed test cases: 1. First, run script lab12test.script to start capturing output. 2. Now, run through the test cases. 3. Press Control-D when you are done. The lab12test.script le will contain a transcript of your session (commands, output, typos and all.) 4. both the shell script and the script output le to your instructor.

10 Lab #12 Page 10 of 11 Part C: Shell Programming Assignment WARNING! You must make your own modications to your own le here. In the past, students have been successfully penalized for academic misconduct -- by copying and submitting another student's code without modication... a grade of zero for all students involved... Please refer to the Niagara College Practice on Academic Honesty for full details. Introduction It's always easier not to make a mistake than to recover from it once the mistake is made. The rst rule to avoid such mistakes is to avoid certain irrevocable commands. UNIX makes it remarkably easy to simply remove entire directory structures without even a warning. Now, this power is impressive, if that is what you are sure you really want to do. But if that wasn't what you had in mind, going "oops" won't help. Instructions The goal of this assignment is to write a shell script to replace the rm command and provide undelete capability. Write a shell program to duplicate the UNIX rm command with the following features: 1. It will have a switch -i that will act in the same manner as in the rm command. 2. Instead of deleting the les, it will move them to a.wastebasket directory. If the le already exists in the.wastebasket directory, the existing le (in.wastebasket) will have the version number 0 (zero) appended to it and the newly deleted le will have version number 1 (one) appended to it. If the version number setup is already in use for that le the newest one will simply have the next version number in the series appended to it. It's your choice as to what system to use for this. Just be sure that it is a unique system and will not be part of any normal le naming convention you might use. 3. It will have a switch -c that will clear the entire wastebasket after asking for conrmation. The -i and -c switches may be combined to ask for conrmation on individual les.

11 Lab #12 Page 11 of 11 Don't forget that wildcards and multiple les are allowed on the command line. The switches when combined may be in any order but must be before any lenames. Your program must also catch any operator errors. Evaluation The program is worth 10 marks. Out of the 10 marks, 2 marks will be assigned for documentation (comments), and 2 marks for style (indenting, etc). This part is worth 75% of the lab.