[echang@wyrd echang]$ echo man ftp
man ftp
[echang@wyrd echang]$

If you type the following command

        [echang@wyrd man_pages]$ echo AN EXAMPLE OF COMMANDS 

The message AN EXAMPLE OF COMMANDS will appear on a line by itself

Punctuation characters

Many symbols, such as angle brackets (> and <) and the semicolon (;), have special meaning to the shell. If you want to echo them in text, you must place the text in quotation marks. For example,

      echo here > there
      echo me; you

will not echo the lines here > there and me; you. (Instead the first command will create a file named "there" and store the text "here" in it; the second will echo "me" and then display a shell error message.)

To echo the entire lines, you must use

      echo "here > there"
      echo "me; you"

Using special character codes in echo

Now suppose we want to put a blank line after the line "AN EXAMPLE OF COMMANDS ". But once you press ENTER (also called a carriage return), the command is completed.

Special characters which are "invisible" or have special meaning such as carriage returns, tabs and quotation marks are commonly encoded in commands and programming languages by a combination of "normal" characters - in Unix, a backslash followed by another character. This is referred to as "escaping" the character. Some frequently used codes are

• \n - newline. When printed, it will start a new line.
• \t - tab
• \" - quotation mark

To use these character codes, you must use the -e option to tell the shell command interpreter to evaluate them as codes instead of as the ordinary characters. You also need to enclose the escaped codes in quotation marks.

example

 
[echang@wyrd man_pages]$ echo AN EXAMPLE OF COMMANDS
[echang@wyrd man_pages]$ echo -e "\n"
[echang@wyrd man_pages]$ date
[echang@wyrd man_pages]$ echo -e "\n"
[echang@wyrd man_pages]$ who

Activity

Try the commands

• echo HELLO
• echo cal
• echo "\n"
• echo -e "\n"

Creating scripts

Echoing blank lines and messages onto the screen may seem strange, but there is a way to automate the process so that you can repeat an entire series of commands by typing a single line.

To create a script of shell commands:

• You must store the commands in a file
• then tell the shell to execute the commands in the file
• The file is called a script.
• The simplest way to to create the file is to use the text editor called pico.

Example, step 1

• First type pico file_name at the shell prompt

  
[echang@wyrd man_pages]$ pico script1

• The pico editor starts up and shows a blank for a new file with nothing in it.
• At the bottom of the screen, the editor shows the commands it understands and the codes for invoking them
• The symbol ^ means to hold down the control key while pressing the letter

 
   UW PICO(tm) 3.5                 File: script1
 
 
 
 
 
 
 

                                  [ New file ]
^G Get Help  ^O WriteOut  ^R Read File ^Y Prev Pg   ^K Cut Text  ^C Cur Pos
^X Exit      ^J Justify   ^W Where is  ^V Next Pg   ^U UnCut Text^T To Spell

Example, step 2

• Type in the commands you want to execute.
• The backspace (or delete, depending on how your telnet client is set up) key erases a character, and the arrow keys can be used to move around in the text.
• Press ^X (Ctrl + X) to exit the pico editor.

 
   UW PICO(tm) 3.5                 File: script1                     Modified

echo An example script file
echo -e "\n"
date
echo -e "\n"
who

^G Get Help  ^O WriteOut  ^R Read File ^Y Prev Pg   ^K Cut Text  ^C Cur Pos
^X Exit      ^J Justify   ^W Where is  ^V Next Pg   ^U UnCut Text^T To Spell

Example, step 3

• Tell the bash shell to execute the script with the command bash file_name.

 
[echang@wyrd ~]$ bash script1
An example script file


Wed Apr 19 11:25:52 EDT 2006


acrum    pts/0        Apr 17 09:17 (orchid.hood.edu)
echang   pts/1        Apr 18 14:47 (70-32-5-123.frdrmd.adelphia.net)

[echang@wyrd ~]$ 

Notice that all of the commands are executed.

File permissions

• Unix is a multi-user operating system. You share wyrd with the other students in your class, and students from many other classes.
• The system uses file permissions to control who can and cannot access your files in different ways.
• Access is controlled at three levels: Owner (you), Group (users with whom you share a group) , Other (the rest of the world).
• Each level may be granted or denied permission to Read, Write, or Execute the file.
• File permissions are shown in long directory listings.
  

• The first letter indicates if it is a directory.

Setting permissions - the chmod command.

• You can set permissions from the command line using the chmod command.
• One way to use it is to give the specific three-digit octal number that represents the permissions you want.
• For example:

     chmod 755 my_filename

• The code you will normally use is 755.
• You can also set file permissions through the SSH file transfer window.
  1. right-click on the file name and choose "properties"
  2. check (or uncheck) the appropriate boxes.
     

Preparing a script for the web.

These instructions will let you call a script through a web server so its output can be seen in the browser.

1. The FIRST TWO LINES in the script must be

   #!/bin/sh
   echo -e "Content-type: text/plain\n\n"
   

   Inportant: be sure that you do not indent the first line.
2. The file MUST be saved with the special filename extension: .cgi For example,

   myscript.cgi

3. The script file MUST be stored in your WWW directory or a subdirectory thereof.
4. The permissions for the script file MUST be executable (use 755).
5. The permissions for the script file AND the directory containing it MUST NOT be writable by group or other.
6. To meet requirements 4 and 5, chmod 755 filename

Seeing the script output

1. Prepare and save the script file.
2. Check all six points listed above
3. Determine the URL for the script (http://wyrd.hood.edu/~your_username/folder_names_if_used/script_file_name.cgi
4. Enter the url into your browser

Example

Here is an example of a shell script that has been modified in this way.

[echang@wyrd WWW]$ cat script2.cgi
#!/bin/bash
echo -e "Content-type: text/plain\n"  
echo "================================="
date
finger
echo -e "\n"   
echo "This is who:"
who
echo -e "\n"
echo "================================="
echo "and this is a calendar:"
cal
echo "================================="
 

Here is a link to the example script. The URL is http://wyrd.hood.edu/~echang/script2.cgi

Lab/Homework Exercise 08

1. Create (use pico) and run a script file which will do the following:
   • print out the date
   • echo the line "This is an example of a script"
   • skip a blank line
   • print out the users on the system
   • skip a blank line
   • print a calendar for the current month, with the weeks beginning on Monday
   • print out your name
2. Run the script, using the bash command, to be sure it works.
3. Modify the script to be callable over the web (add the initial two lines and change the file permissions)
4. Test to see that it works.
5. Put a link to the script file on your table of contents page
6. Complete the Submission on Blackboard.