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{{Admon/tip|Bash Shell Scripting Tips:|<br><ul><li>'''The case statementawk Command:'''<br><br>The case statement is a control-flow statement that works in a similar way as the if-elif-else statement (but is more concise). This statement presents scenerios or "cases" based on values or regular expressions (not ranges of values like if-elif-else statements). After action(s) are taken for a particular scenerio (or "case"), a break statement (''';;x''') is used to "break-out" of the statement (and not perform other actions). A default case (*) is also used to catch exceptions.<br><br><u>'''Examples (try in shell script):'''</u><br><br>''read -p "pick a door (1 or 2): " pick<br>case $pick in<br> 1) echo "You win a car!" ;;<br> 2) echo "You win a bag of dirt!" ;;<br> *) echo "Not a valid entry"<br> exit 1 ;;<br>esac''<br><br>''read -p "enter a single digit: " digit<br>case $digit in<br> [0-9]) echo "Your single digit is: $digit" ;;<br> *) echo "not a valid single digit"<br> exit 1 ;;<br>esac''<br><br></li><li>'''The getopts functionScheduling Tasks:'''<br><br></li></ul>The getopts function allows the shell scripter to create scripts that accept options (like options for Linux commands). This provides the Linux administrator with scripts that provide more flexibility and versatility. A built-in function called '''getopts''' (i.e. get command options) is used in conjunction with a '''while''' loop and a '''case''' statement to carry out actions based on if certain options are present when the shell script is run. The variable '''$OPTARG''' can be used if an option accepts text (denoted in the getopts function with an option letter followed by a colon. Case statement exceptions use the '''crontab:)''' and '''\?)''' cases for error handling.<br><br>'''<u>Example of getopts</u>''' (try in script and run with options)<br><br>'x'while getopts abc: name<br>do<br> case $name in<br> a) echo "Action for option \"a\"" ;;<br> b) echo "Action for option \"b\"" ;;<br> c) echo "Action for option \"c\""<br> echo Value is: $OPTARG" ;;<br> :) echo "Error: You need text after -c option"<br> exit 1 ;;<br> \?) echo "Error: Incorrect option"<br> exit 1 ;;<br>esac''<br><br>}}
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#Download, study, and run the following shell script. Issue the command:<br><b><code><span style=" pointer-events:none;cursor:default;color:#3366CC;font-size:1.2em;">wget https://scs.senecac.on.ca/~murray.saul/usermonitor-createdisk-space.bash</span></code></b>#Try to understand what these Bash Shell scripts do, and then run the script as root. After running the shell script, view the contents of the '''/home''' directory to confirm.
Although the '''zenity''' command is a "user-friendly" way to run shell scripts, Linux administrators usually create shell scripts that resemble common Linux commands. In this lab, you will learn to create a shell script using the getopts function to make your shell script behave more like actual Linux commands (including the use of options). Refer to the notes section on the right-hand-side for reference about the '''case''' statement and the '''getopts''' function.Setup crontab
<ol><li value="3">Open a Bash shell terminal and login as root.</li><li>Use the wget command to download the input file called user-data.txt by issuing the command:<br><b><code><span style="color:#3366CC;font-size:1.2em;">wget https://scs.senecac.on.ca/~murray.saul/user-data.txt</span></code></b></li><li>View the contents on the user-data.txt file to confirm there are 3 fields (username, fullname, and e-mail address)which are separated by the colon (:) symbol.<li><li>Use a text editor (such as <b><code><span style="color:#3366CC;font-size:1.2em;">vi</span></code></b> or <b><code><span style="color:#3366CC;font-size:1.2em;">nano</span></code></b>) to create a Bash Shell script called: <b><code><span style="color:#3366CC;font-size:1.2em;">createUsers.bash</span></code></b> in /root's home directory.</li><li>Enter the following text content into your text-editing session:</li></ol>
<code style="color:#3366CC;font-family:courier;font-size:.9em;margin-left:20px;">
<br>
#!/bin/bash <br>
<br>
# createUsers.bash<br>
# Purpose: Generates a batch of user accounts (user data stored in a text file)<br>
#<br># USAGE:<br>
#<br># /root/createUsers.bash [-i {input-path}] <br>
#<br>
# Author: *** INSERT YOUR NAME ***<br>
# Date: *** CURRENT DATE ***<br>
<br>
if [ $PWD != "/root" ] # only runs if in root's home directory<br>
then<br> echo "You must be in root's home directory." >&2<br>
exit 1<br>
fi<br>
if [ "$#" -eq 0 ] # if no arguments after command<br>
then<br>
echo "You must enter an argument" >&2<br>
echo "USAGE: $0 [-i {input-path}]" >&2<br>
exit 2<br>
fi<br>
</code>
<br>
<ol><li value="6">Save your editing session, but remain in the text editor.</li><li>The code displayed below uses the getopt function set the input file pathname or check for invalid options or missing option text. Add the following code</li></ol>
<br>
<code style="color:#3366CC;font-family:courier;font-size:.9em;">
<br>
outputFlag="n"<br>
while getopts i: name<br>
do<br>
case $name in<br>
i) inputFile=$OPTARG ;;<br>
:) echo "Error: You need text after options requiring text"<br>
exit 1 ;;<br>
\?) echo "Error: Incorrect option"<br>
exit 1 ;;<br>
esac<br>
done<br>
</code>
<ol><li value="6">Save your editing session, but remain in the text editor.</li><li>The code displayed below uses logic to exit the script if the input file does not exist. Command substitution is used to store each line of the input file as a positional parameter. There is one subtle problem here: The full names of the users contain spaces which can create havoc when trying to set each line as a separate positional parameter. In this case the sed command is used to convert spaces to plus signs (+), which will be converted back later. Finally, a '''for''' loop is used to create each account ('''useradd''') and mail the user their account information ('''mail'''). Add the following code:</li></ol>
<br>
<code style="color:#3366CC;font-family:courier;font-size:.9em;">
<br>
if [ ! -f $inputFile ]<br>
then<br>
echo "The file pathname \"$inputFile\" is empty or does not exist" >&2<br>
exit 2<br>
fi<br>
<br>
set $(sed 's/ /+/g' $inputFile) # temporarily convert spaces to + for storing lines as positional parameters<br>
<br>
for x<br>
do<br>
useradd -m -c "$(echo $x | cut -d":" -f2 | sed 's/+/ /g')" -p $(date | md5sum | cut -d" " -f1) $(echo $x | cut -d":" -f1)<br>
mail -s "Server Account Information" $(echo $x | cut -d":" -f3) <<+<br>
Here is your server account information:<br>
servername: myserver.senecac.on.ca<br>
username: $(echo $x | cut -d":" -f1)<br>
password: $(date | md5sum | cut -d" " -f1)<br>
Regards,<br>
IT Department<br>
+<br>
done<br>
<br>
echo -e "\n\nAccounts have been created\n\n"<br>
exit 0<br>
</code>
<ol>
<li value="8">Save, set permissions, and then run that shell script for the input text file '''user-data.txt'''. Did it work? Try running the script without an argument - What did it do? </li><li>You have completed lab4. Proceed to Completing The Lab, and follow the instructions for "lab sign-off".</li></ol>
'''Answer Investigation 3 observations / questions in your lab log book.'''
