Assignment Detail:- KIT501 ICT Systems Administration Fundamentals - University of Tasmania
Goal
The main purpose of this practical is to give you more familiarity with iteration -looping- within UNIX shell scripts, and it also introduces another loop syntax, the for loop-
1- UNIX Shell Scripting - Looping - First Sample Script
The following sample script -and the sample script in section 2- reinforce the looping concept in UNIX scripts-
Hands-on exercises
A Under your kit501 directory, change into the directory named Looping which you created last week- If you have removed it, create it now -and change into it--B Create a script which must be named as cpback-sh, with the following content- For time considerations, you do not need to type the comment lines into your script -except for the first line-, however in any scripts you write -for example the scripting assignment-, comments are needed- Comments are there to help you understand the script- The first special comment the beginning is needed as it determines which shell is used to run the commands that follow-
#! /bin/sh
# This program copies a file into a safe directory without# overwriting- For example, it copies a file named foo to foo-1 # if foo exists in the destination directory, or to foo-2# if foo-1 exists in the destination directory-
# To run the script, two arguments are required in the command line, # a source file, followed by a destination directory- Without two# arguments, the scrip displays the usage information, and exits
if - $# -ne 2 -; thenecho "Usage: $0 source destination"; exit
# The script also requires that the second argument must be an # existing directory file, if not, displays an error message # and exits
elif - ! -d $2 -; thenecho "Directory does not exist"; exit else# assign the first argument -the source filename- as value # to variable filefile=$1
# If the source file does not exist in the destination directory, # then simply copy it into the directoryif - ! -f $2/$file -; then cp $1 $2
# But if the source file does exist in the destination directory, # then we have to do something to avoid overwritingelsecopies=1 # The variable copies takes 1 as initial value while truedoif - ! -f $2/$file-$copies -; then cp $1 $2/$1-$copiesecho "File $1 copied to $1-$copies" breakelsecopies=`expr $copies + 1`fi donefifiSave the content of the script- Assign execute permission to the script-
To run the script, you need a support source file and a support destination directory-
Create a support text file named foo- One quick way to do this is to redirect the output of a command line into the file: -this example copies the output of the man page for the man command into the file called foo-
$ man man > fooCreate a support directory named safedir- Run the script as follows:$ -/cpback foo safedir
Run the command line two more times:$ -/cpback foo safedir$ -/cpback foo safedir
Use ls to list all the file names stored under safedir- Has any file overwriting occurred????
2- UNIX Shell Scripting - Looping - Second Sample Script
The following example shows some pattern-matching using case statement based on user's input-
Hands-on exercises
Create a script which must be named as dentry-sh, with the following content- You do not need to type the comment lines into your script- They are there to help you understand the script-
Please note that this is a script with nested loop structure, that is, an inner loop is contained within an outer loop-
# This script repeatedly accepts a two-digit code -such as 01, 02, etc- and# its corresponding description -such as engineer- from keyboard, performs# some validation checks, and then adds the entry into a text file named # newlist
# First create a new blank text file named newlist, if it does not currently# existif - ! -f newlist -; then touch newlistfi
# Start the outer loop by prompting the user to enter a code while echo -e "Designation code: \c"doread codecase "$code" in# Ensure the two-digit code is in correct format, # and does not currently exist-0-9--0-9-- if grep "$code" newlist > /dev/null; then echo "Code exists"continue fi ;;*- echo "Invalid code" continue ;;esac
# Start the inner loop by prompting the user to enter a description while echo -e "Description: \c";doread desc
case "$desc" in# This is how to ensure that the user has entered a valid # description,n which contains letters and spaces only*-!\ a-zA-Z-*- echo "Can contain only letters and spaces" continue ;;
# If the user simply presses the Enter key, without typing anything ""- echo "Description not entered"continue ;;
# The user has entered a valid description, add it together with # the previously entered valid code into the file*- echo "$code|$desc" >> newlist break ;;esac done
echo -e "\nEnter another entry???? -y/n-: \c" read answercase "$answer" in -yY-*- continue ;;*- break ;;esac done
B Save the content of the script- Assign execute permission to the script-
Run the script by entering the following codes and descriptions, respectively:
01 student02 engineer03 chefC Check the content of the newlist file to verify the above entries-
3- UNIX Shell Scripting - The for Loop - Looping with a list
The general format of for loop is as follows:
for variable in listdocommandsdone
• list can be any sequence of items, for example, strings, numbers, or even filenames-• variable is the control variable- Each iteration its value is the next item in the list- Use$variable to evaluate -retrieve- the value-• commands are one or more commands to execute each iteration-
Iterating for all items in an explicit listThe following example shows how to do something with every item in an explicit list:
for item in item1 item2 item3 doecho "The item is: $item"done
3-1 Hands-on exercises
A Ensure that your present working directory is Looping, which is under your kit501 directory-
Make a new directory named forloop -under Looping- and change into the new directory-B Create 3 text files which must be named as chap20, chap21, and chap22, respectively, by simply redirecting outputs of some echo commands:
$ echo "content of chap20" > chap20$ echo "content of chap21" > chap21$ echo "content of chap22" > chap22
Verify that the 3 files have been created with the correct content-C Create a script which must be named as ftest-sh, with the following content:
for file in chap20 chap21 chap22 docp $file "$file-bak"echo $file copied to "$file-bak"done
In this script, file is a variable, which takes chap20 as its value first- Then the loop body is entered, which copies chap20 to chap20-bak, and displays a message to confirm the operation- Then the loop is repeated, with the variable file taking chap21 as its value this time, making a backup copy for chap21 and displaying a message confirming the operation- Then the loop is repeated again, with the variable file taking chap22 as its value, making a backup copy for chap22 and displaying a message confirming the operation- Now that all the files in the list have been manipulated, the loop ends-
Save the content- Assign execute permission to the script-
Run the script- Observe the outputs- Verify that all the backup files have been created-D What if you want to make a backup copy of each file stored under the current directory, and there are currently 300 files available -under the current directory-- Do you have to specify each filename in the list explicitly???? You do not want to do this!An approach is the following:
for file in `ls -p | grep -v /` docp $file "$file-bak"echo $file copied to "$file-bak"done
Note the command substitution used in the first line with the ls command- No matter how many files are stored under the current directory, the output of ls will retrieve all of them! The -p option tells ls to put a slash character after directory names- The grep -v / part means only show lines that do not contain the / character - this is one way to only find files -and exclude directory names-- Of course, if the current directory only contains files, then just`ls` by itself will work as well-
Modify the first statement in your ftest-sh so that it uses `ls` rather than an explicit list- Remove all the existing -bak files under the current directory- Run the script again- You will see that it also makes a backup copy of the script itself-
Remove all the -bak files again-E Think about what the following script does:
for file in *-html *-htm dogzip $filedone
Attachment:- ICT Systems Administration Fundamentals-rar
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