Welcome to Episode 3

This episode is mostly about variables, which are names for places in memory where you will store values. Values can be strings of characters or numbers. Bash doesn’t require you to choose which type of value you are going to use to fill your variable.

Variables in Bash Scripting

The script below shows how to assign and use a simple variable. In general, shell variables are all treated as strings. A string is a series of characters, the content of which are ignored by the shell. Shell programming required you to get the syntax right. In the assignment there must be no space between the variable name and the equals sign, or the equals sign and the value. To use the variable, it is prefixed by a dollar ‘$‘ character.

#!/bin/sh
# name is a variable
name="Ferdinand" # This is an assignment of a value to a variable
                 #  called “name.”
echo "The name is $name"  # This line is calling the variable
                          #  called name.

The script above would generate a line that read, “The name is Ferdinand”

The special variables $1-$9 correspond to the arguments passed to the script when it is invoked. For example, if we rewrite the script above as shown below, calling the script Yourname.sh, and then invoke the command Yourname.sh Ferdinand Quacker, the message “Your name is Ferdinand Quacker” will be printed out:

#!/bin/sh
# Yourname.sh
echo "Your name is $1 $2"

wolf@Lab5-ubustudio:~$ sudo chmod +x Yourname.sh 
[sudo] password for wolf: 
wolf@Lab5-ubustudio:~$ ./Yourname.sh      
Your name is  
wolf@Lab5-ubustudio:~$ ./Yourname.sh Ferdinand Quacker 
Your name is Ferdinand Quacker 

Where I “forgot” to define the variables $1 and $2, the script ran great but produced no visible output.

Naming Conventions in Bash Scripting

You can choose almost any name for your variables, and textbooks often use one-letter variable names such as “A,” “B” and “C.” This makes a short example for the textbook, and in certain situations is the best kind of name for a variable. Some requirements of bash variable names are that they cannot contain spaces and they cannot start with a digit. Many sources for bash scripting help suggest you always use upper-case letters in a variable name, like “WEIGHT,” or that you always use lower-case letters, like “weight.” It is most important to keep some regularity in your variable-naming.

The most common conventions are

Single word: Where the name of the variable is a single word that is descriptive of what the content of the variable will be. “height,” “weight,” “colour,” “description” or understandable shortenings of the words like “desc,” “mnths,” “hght,” and so on. Keep in mind that the name of a variable can help future readers of your code to understand what you meant the script to do. That future reader might be you!

Underscore_Separated words: Where the variable name is two or more words separated by an underscore. Underscore is the name for the character that results from holding the shift key down and tapping the hyphen or dash. “_” between words is treated by the shell program as if there is no space between the words but is readable as if there is a space, e.g., “points_scored,” “monthly_expenses,” “sum_of_entries” This convention makes the code easier to read.

CamelCase or StudlyCapitals: CamelCase uses two or more words to name a variable, but instead of an underscore, camelCasing capitalizes the first letter of the internal words.

Arithmetic in Bash Scripting

Shell scripts can also do math but it is not a great way to spend your (computer’s) time. The script below will produce a Fibonacci sequence. A Fibonacci sequence takes one number and adds the next number to it to produce the third in the sequence and then takes #’s 2 and 3 to make #4 in the sequence and so on. In a Fibonacci sequence, denoted by F₀ , F₁ , F₂ , F₃ , F₄ , … [where the subscribed numbers ( 0, 1, 2, 3, 4 , … ) are indices identifying the consecutive members of the sequence], any member is the sum of its two immediate predecessors. Thus, beginning with F₀ = 0 and F₁ = 1 , for j = 2, 3, 4 , 5, … , every F_j = F_j-1 + F_j-2 .” If you set the MAX constant to 40, you will notice that it takes more than twice as much time as calculating 20 entries in the Fibonacci series. Simple formulae work quickly enough, but long and complicated formulae may work better in in compiled programs. There are ways to have Bash scripts call compiled program modules, so there is no problem if you really must have a complicated problem to solve.

#!/bin/bash 
# fibonacci.sh : Fibonacci sequence 

MAX=20     # a constant, denoting Number of terms (+1) to generate. 
MIN=2      # another constant. 
           #If index is less than 2, then Fibo(index) = index. 

Fibonacci () 
{ 
  fsn=$1   
  if [ "$fsn" -lt "$MIN" ] 
  then 
    echo "$fsn"  # First two terms are 0 1 ... see above. 
  else 
    (( --fsn ))  # j-1 
    term1=$( Fibonacci $fsn )   #  Fibo(j-1) 

    (( --fsn ))  # j-2 
    term2=$( Fibonacci $fsn )   #  Fibo(j-2) 

    echo $(( term1 + term2 )) 
  fi 
}

for i in $(seq 0 $MAX) 
do  # Calculate $MAX+1 terms. 
  FIBO=$(Fibonacci $i) 
  echo -n "$FIBO " 
done 
# expected output:
#  0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181 6765

echo  " "
exit 0

If you copy the script into a file and run it, the first few numbers are found quite rapidly, but you could produce the last 10 places in the sequence on paper or (possibly) in your head without a calculator before the shell script could find them.

Shell Variables

Like every other programming language, shells support variables. Shell variables may be assigned values, manipulated, and used. Some variables are automatically assigned for use by the shell. Some variables are environmental variables. These variables can effect how programs run outside of the shell, and you might want to be careful naming your shell variables the same as any of these. The following is a list of the environmental variables on Lab5-ubustudio. Note: I am calling the env list from a different directory, and it is all in my command prompt. Your machine might only show you only the last directory in the path. You can customize this by changing the Environmental Variable that holds the prompt information. That Variable is PS1 at the top of the abbreviated list below. You may notice that the Environmental Variables below are all centered around a specific user If somebody else were to log in to this machine, a lot of the Environmental Variables would be changed. Another way to look at how your system is set up is to type set at the command line. That will show you even more Environmental Variables.

wolf@Lab5-ubustudio:~/Documents/Projects/basho$ env

PS1=’\[\e]0;\u@\h: \w\a\]${debian_chroot:+($debian_chroot)}\u@\h:\w\$ ‘

ORBIT_SOCKETDIR=/tmp/orbit-wolf

TERM=xterm

SHELL=/bin/bash

USER=wolf

USERNAME=wolf

XDG_CONFIG_DIRS=/usr/share/ubuntustudio-menu/:/etc/xdg/

DESKTOP_SESSION=gnome

PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games

PWD=/home/wolf/Documents/Projects/basho

GDM_KEYBOARD_LAYOUT=us

LANG=en_US.UTF-8

GDM_LANG=en_US.UTF-8

GDMSESSION=gnome

SHLVL=1

HOME=/home/wolf

LOGNAME=wolf

COLORTERM=gnome-terminal

This is the end of episode 3.  Please stay tuned for another riveting episode soon.

== Wolf Halton is CEO of Atlanta Cloud Technology, Inc. ,  a guest writer on security topics here, at  and owner of Wolfhalton.info.

This is the start of a serialized article

It was started to explain certain features of the bash shell scripting language. I will be posting it across several weeks as time permits.  please feel free to ask questions and we can answer them.  When the entire article has been serialized, I will send it for free to people who have offered comments.

(Another) simple bash script

If you just type a series of commands into a file and make the file executable, the Linux bash shell will try to run the script as if it is a script written for a bash shell since that is the shell you are probably using if you are running Ubuntu, or many other Linuxes. Scripts for the c-shell or the z-shell might well fail under those conditions, so, to make sure the correct shell is invoked, the first line of the shell-script file should always tell the system what shell is to be invoked. Below is illustrated a simple Bash script: it just outputs the message “hello Linux User!”:

#!/bin/sh
# hello.sh this is the name of the file, and is just a reminder
# for you what you called it.
echo "hello Linux User!"
# This is a comment line, anything that follows a '#' sign
# is a comment.  Comments make a script more readable

Use a text editor, such as vi, nano (for the terminal), gedit or kate (for the GUI), to create a file with the lines above in it.  Personally, I recommend nano and kate in that order.   Save the file, calling it hello.sh. Then make the hello.sh file executable by typing:

$ sudo chmod 755 hello.sh

This uses the “octal permissions” feature of chmod. It makes the file executable for the owner (probably you, or root), the group and for everybody else.  You can then run the script by simply typing ./hello.sh This tells Linux that the file is a script, it is in the directory from which you are calling it, and runs the Linux commands inside it (in this case, just the echo command).  [Note: if you are hosting multiple users, you will have to put the files somewhere anybody can get at them, such as /usr/local/bin, in which case you would want to make sure they are owned by root.   Then anybody with a sign-in can run the file just by typing hello.sh ]

You can give your shell scripts almost any name you like. There are times when there might be another script built in to your distribution with the same name. Here is the content of the /bin directory of this Ubuntu 9.10 Linux box. Please note that your machine will put in the [name]@[computername]:[directory][access-level] sequence for your prompt as mine put in [wolf]@[Lab5-ubustudio]:[~][$]. If your access-level is shown as [#] then you are acting as root, or the administrative user for that sequence. If you are in the habit of starting sessions as root, this is a marvelous time to break that dangerous habit. In Ubuntu or Debian Linux distributions, you rarely see the root symbol as they use the sudo command to act as pseudo-root for just as long as you need to. Acting as root, when it isn’t required, should be avoided as a general rule.

If you just can’t avoid using one of these as a filename for your script, add the .sh and keep it in your home directory in a special file, or on your thumb-drive, and invoke your scripts from their own directory with the ./ sequence. You can check whether your name exists by using the which command. Which tells you where a specific command exists, if it does, and doesn’t tell you that it doesn’t exist, if it doesn’t. For instance to see if there are commands called open and sesame, type:

wolf@Lab5-ubustudio:~$ which open 
/bin/open 
wolf@Lab5-ubustudio:~$ which sesame 
wolf@Lab5-ubustudio:~$ 

Note the lack of response when you ask for something that doesn’t exist.

This is the end of episode 1.  Please stay tuned for another riveting episode soon.

== Wolf Halton is CEO of Atlanta Cloud Technology, Inc. ,  a guest writer on security topics here, at  and owner of Wolfhalton.info.

Ubuntu GNU/Linux has become one of my favorite Open Source operating systems. It is free, easy to install, secure and at the time of this writing has over 29,000 free software packages available which can be easily installed and removed using its GUI software package manager.

If you have some other type of laptop you are advised to check at linux-laptop.net for reports of successful installations of GNU/Linux on it. I would further advise that you should install the distribution of GNU/Linux on your laptop that has the best reports of successful install posted at linux-laptop.net. Another good resource for checking Ubuntu hardware comparability is UbuntuHCL.org. Or the Ubuntu Laptop Testing Team. If one can successfully install older versions of Ubuntu onto a particular laptop then they should see good results installing Ubuntu 10.04.

Step 1: Download the Ubuntu 10.04 installation CD from the Ubuntu 10.04 download page. Visit that page and click “Begin Download”. This will begin the download of a .iso file.

Once the download is complete check the size of the .iso file. If the size of the .iso file is not around 699MB in size it will not work and you will need to use a BitTorrent transfer client to download the file instead.

The latest version of .torrent seed files can be found here. Once the .iso.torrent seed file has downloaded add it to your BitTorrent transmission client and download the .iso with the BitTorrent client. If you don’t already have a BitTorrent client you can get one here. BitTorrent offers more reliable downloads of large files, is sometimes faster and I recommend its use.

Step 2: Once you have obtained a good .iso file you must “burn” the .iso image onto a CD. Simply copying the file to a CD is not sufficient. Instructions on how to burn the .iso image can be found…

• Here if you are using Windows XP/Vista.
• Here if you are using Mac OS.

Step 3: Connect the network port on the computer to your router. Insert the CD created from Step 2 into the CD drive of the computer you wish to install Ubuntu 10.04 onto then restart the machine.

When the machine boots to the install CD one will be presented with a language chooser that allows them to select the language of choice for the install. Choose “English” and press “Enter” on the keyboard. Next the Ubuntu installer will present five options for one to choose from. One may select any option they desire here, however, we will choose the first option “Install Ubuntu” and press “Enter”.

Next one will be presented with another language chooser we will again choose “English” and press the “Enter” key. Next one will be asked to select their location. Select your location and press “Enter”. Next you will be asked if you want to check your key-board layout. Accept the recommendation (ours was “No”) and press “Enter”. Next you will be asked the origin of your keyboard. Here we select “United States” and press “Enter”. Next you are asked to identify the keyboard layout. We will select “USA” and press “Enter”.

After some software loads from the CD you will be asked to select the primary network interface. Select eth0 and press “Enter”. When the network is successfully configured you will be asked to provide a “Hostname”. Choose a hostname for the computer or simply accept the default “ubuntu” and press “Enter”. Next a time zone chooser will appear. Select your time zone and press “Enter”.

Next you will be presented with partition options for the install. We will choose “Guided – use entire disk”, however, one can choose any they wish. Next you will be asked to choose the disk to partition we will choose “SCSIx …” and press “Enter”. You will be asked if the new partition scheme is okay. Select “Yes” and press “Enter”. Now the base system will be installed.

Next one will be asked to enter their full name. Enter your name and press “Enter”. Next you will be asked for a user name that will be your login name. You may accept the recommendation or choose your own but it must be all lower-case. Next you will be asked to choose a password and then reenter the password to confirm it. Do that and press “Enter”. Next you will be asked if you want to have your home directory encrypted. Accept the recommendation and press “Enter”.

Next one will be asked if a network proxy is required. We will leave this blank because I do not use a proxy at my location and press “Enter”.

Next the installer will continue and install the required software. This can take some time.

When the software has been installed one will be asked if this is the only operating system on the computer and if they want to install the GRUB boot loader to the master boot record. If you followed these instructions then it is and you should accept the recommendation of “Yes” and press “Enter”. Next one will be asked if the system clock is set to UTC. Select “Yes” and press “Enter”. After this the installation is complete. One will be asked to remove the CD from the tray and reboot the machine. Do this when asked to. Select “Continue” and press “Enter”.

When the machine reboots to the new Ubuntu installation login to your new account.

After one has joined a WiFi network one can now disconnect the network cable from the computer and the router.

At this point one should follow the instructions here to activate all of the multi-media functions.

Now all the Ubuntu 10.04 software is installed and ready for use and the multi-media functions are enabled.

Over all I am pleased and impressed with this new version of Ubuntu. If you followed my previous articles on how to install Ubuntu version 9.10 you can upgrade to 10.04 by simply clicking the “Upgrade” button in System>Administration>Update Manager.

Once you have completed the upgrade to Ubuntu 10.04 you will have to upgrade the flash player by visiting youtube and trying to watch a video. When you do this you will be told you have to upgrade your flash player. Just follow the link and the subsequent instructions to do get that stuff working.

Ubuntu Studio is the Ubuntu multi-media producer version of Linux. I have found that it works well for audio production. The directions here will install a Digital Audio Workstation (DAW) an assortment of software synthesizers and drum machines all of which are open source free software.

If you have some other brand of laptop you are advised to check at linux-laptop.net for reports of successful installations of Linux on it. I would further advise that you should install the distribution of Linux on your laptop that has the best reports of successful install posted at linux-laptop.net. However Ubuntu has an easy, intuitive dual boot option built into its installer. Another good resource for checking Ubuntu hardware comparability is UbuntuHCL.org. Or the Ubuntu Laptop Testing Team. If one can successfully install regular Ubuntu onto a particular laptop then they should see good results installing Ubuntu Studio.

Step 1: Download the Ubuntu Studio installation DVD from the Ubuntu Studio download page. Visit that page, select the appropriate version for your computer and click the “Download” link. This will begin the download of a .iso file.

Once the download is complete check the size of the .iso file. If the size of the .iso file is not around 1.4GB in size it will not work and you will need to use a BitTorrent transfer client to download the file instead.

The latest version of .torrent seed files can be found here. Once the .iso.torrent seed file has downloaded add it to your BitTorrent transmition client and download the .iso with the BitTorrent client. If you don’t already have a BitTorrent client you can get one here. BitTorrent offers more reliable downloads of large files and is sometimes faster.

Step 2: Once you have obtained a good .iso file you must “burn” the .iso image onto a DVD. Simply copying the file to a DVD is not sufficient. Instructions on how to burn the .iso image can be found…

• Here if you are using Windows XP/Vista.
• Here if you are using Mac OS.

Be sure that the machine you use to burn the DVD has DVD-RW capability. The IBM T60 does not.

Step 3: Connect the network port on the computer to your router. Ubuntu Studio 9.10 does not have the wireless stuff included by default. We will install that later. Insert the DVD created from Step 2 into the CD/DVD drive of the laptop you wish to install Ubuntu Studio onto then restart the machine.

When the machine boots to the install DVD one will be presented with a language chooser that allows them to select the language of choice for the install. Choose the language of your choice and press “Enter” on the keyboard. Next the Ubuntu Studio installer will present five options for one to choose from. One may select any option they desire here, however, we will choose the first option “Install Ubuntu Studio” and press “Enter”.

Next one will be presented with another language chooser we will choose “English” and press the “Enter” key. Next one will be asked to select their location. Select your location and press “Enter”. Next you will be asked if you want to check your key-board layout. Accept the recommendation (ours was “No”) and press “Enter”. Next you will be asked the origin of your keyboard. Here we select “United States” and press “Enter”. Next you are asked to identify the keyboard layout. We will select “USA” and press “Enter”.

After some software loads from the DVD you will be asked to select the primary network interface. Select eth0 and press “Enter”. When the network is successfully configured you will be asked to provide a “Hostname”. Choose a hostname for the computer or simply accept the default “ubuntu” and press “Enter”. Next a time zone chooser will appear. Select your time zone and press “Enter”.

Next you will be presented with partition options for the install. We will choose “Guided – use entire disk”, however, one can choose any they wish. Next you will be asked to choose the disk to partition we will choose “SCSI1 …” and press “Enter”. You will be asked if the new partition scheme is okay. Select “Yes” and press “Enter”. Now the base system will be installed.

Next one will be asked to enter their full name. Enter your name and press “Enter”. Next you will be asked for a user name that will be your login name. You may accept the recommendation or choose your own but it must be all lower-case. Next you will be asked to choose a password and then reenter the password to confirm it. Do that and press “Enter”. Next you will be asked if you want to have your home directory encrypted. Accept the recommendation and press “Enter”.

Next one will be asked if a network proxy is required. We will leave this blank because I do not use a proxy at my location and press “Enter”. Next one will be asked to select the software they want to install. We will use the space-bar to select all packages and press “Enter”.

Next the installer will continue and install the software required based on your selections in the last step. This can take some time.

When the software has been installed one will be asked if the clock is set to UTC. Accept the recommendation and press “Enter” after this the installation is complete. One will be asked to remove the DVD from the tray and reboot the machine. Do this now.

When the machine reboots to the new Ubuntu Studio install login to your new account. Click on the Ubuntu Studio icon in the upper left corner of the screen then select System>Administration>Synaptic Packgage Manager. Enter your password and press “Enter”. Click on “Search” and then type “network-manager” into the search input box and press “Enter”. Click on the check-box to the left of “network-manager” in the right-hand column and then select “mark for installation”. Click “Mark” for the additional required changes. Click the “Apply” under the green check mark on the application control panel then click “Apply” in the subsequent “Summary” dialog. When prompted restart the machine do so.

When one logs into their account now the Network Manager icon will appear in the applet panel on the top right of the screen. One can configure the WiFi network adapters after clicking on this icon.

After one has joined a WiFi network the network cable between the computer and the router can be removed.

At this point one should follow the instructions here to activate all of the multi-media functions.

Now all the Ubuntu Studio 9.10 software is installed and ready for use and the multi-media functions are enabled. Of course if one wants to use peripheral devices they will have to configure the relevant applications for them. One can find instructions on how to do this by searching on the web.

This author has been using a ZOOM G2.1u configured with the instructions here as the guitar interface.

Perhaps the most advanced open source guitar effects application is Rakarrack which can be downloaded here then compiled and installed by following the instructions here.

Ubuntu has become one of my favorite Open Source operating systems. It is free, easy to install, secure and at the time of this writing has over 29,000 free software packages available which can be easily installed and removed using its GUI software package manager. Ubuntu can install and configure itself for dual-boot during the install process or one can choose to dedicate the entire capacity of the hard-disk to the Ubuntu system. We will accept the recommended dual boot configuration during the install process.

I invite everyone to consider Ubuntu installed on a used laptop as a fall-back from their PC or Mac regardless of type you prefer. You will be glad you did.

About The IBM Lenovo T60 Think Pad (T60): I have a number of T60 laptops and they have proved to be a robust vehicle for the Ubuntu Linux operating system. At the time of this writing the T60 can be purchased used, in good condition for around $200 on ebay. Be sure to get one with an internal WiFi card already installed. In my opinion this hardware and operating system scenario is one of the best ways for someone to get started with the Linux operating system.

If you have some other brand of laptop you are advised to check at linux-laptop.net for reports of successful installations of Linux on it. I would further advise that you should install the distribution of Linux on your laptop that has the best reports of successful install posted at linux-laptop.net. However Ubuntu has an easy, intuitive dual boot option built into its installer. Another good resource for checking Ubuntu hardware comparability is UbuntuHCL.org. Or the Ubuntu Laptop Testing Team.

I have found that older laptops that originally ran Window XP are excellent candidates for use with Ubuntu as are newer Apple “MacBooks”.

With the preliminaries out of the way lets begin.

Step 1: Download the Ubuntu installation CD from the Ubuntu download page. Visit that page, select the .iso for your architecture (we will use x86). This will begin the download of a .iso file.

Once the download is complete check the size of the .iso file. If the size of the .iso file is not around 690MB in size it will not work and you will need to use a BitTorrent transfer client to download the file instead. The torrent seed file for Ubuntu 9.10 Desktop Edition can be found here. Once the .iso.torrent seed file has downloaded add it to your BitTorrent transmition client and download the .iso with the BitTorrent client. If you don’t already have a BitTorrent client you can get one here. BitTorrent offers more reliable downloads of large files and is sometimes faster.

Step 2: Once you have obtained a good .iso file you must “burn” the .iso image onto a CD. Simply copying the file to a CD is not sufficient. Instructions on how to burn the .iso image to CD can be found…

• Here if you are using Windows XP/Vista.
• Here if you are using Mac OS.

Step 3: Insert the CD created from Step 2 into the CDROM of the laptop you wish to install Ubuntu onto then restart the machine.

When the machine boots to the install CD one will be presented with a language chooser that allows them to select the language of choice for the install. One has 30 seconds to choose a install language other than English (the default) or the system will boot into an Ubuntu “Live” mode where you can try Ubuntu on your laptop without any changes to your hard disk. If you let this happen and you are ready to install Ubuntu onto your computer click the “Install Ubuntu” icon on the desktop of the “Live” session and you will begin the installation. If you don’t want to wait 30 seconds choose “English” and press “Enter” on the keyboard.

Next the Ubuntu installer will present five options for one to choose from. One may select any option they they desire here, however, we will choose the second option “Install Ubuntu”. This will start the installation process. After some files are loaded from the install CD you will be presented with a “Welcome” screen where you have a second chance to select the install language and if you have internet access review the “Release Notes”. Click on the “Forward” button. Next you will be asked to select your location with a location chooser screen. Select your location and click the “Forward” button. Next you will be asked about your keyboard layout. Just accept the suggested choice and click the “Forward” button.

Next you will be asked to specify the new disk partition arrangement. Default is dual boot and the partitioner will suggest that you install Ubuntu side-by-side with the computers current OS. Accept the recommended configuration and click the “Forward” button. A warning dialog will pop-up and ask if you are sure you want to accept the new partition scheme because it cannot be undone. Click the “Continue” button. The next step can take some time because of the coalescence required on the disk before a second OS can be installed on it.

After space is made for the new partition that will contain Ubuntu you will be asked “Who are you?”. Enter you name, your login name, password and name you would like the machine to display on the network. Accept the recommended “Require password for login” and click the “Forward” button. You may be asked if you want to “Migrate documents and settings” check the ones that you want and click the “Forward” button.

The “Ready to install” screen will be displayed giving you a chance to review the settings you have selected. Just click the “Install” button. Your disk will be partitioned and the new system installed onto the hard disk. This phase may take some time but it is the home stretch of the install.

When the installation is complete a dialog will pop up and ask you to restart the computer.  Click “Restart Now”, you will be asked to remove the CD and press “Enter” so do it. When the computer reboots select the OS you want to use for the pending session and press “Enter”. You will boot to that system.

If you have difficulty you can post questions in the Ubuntu Forums. If you have comments or questions for me you can leave them as comments below until the time for their submission has expired (a few weeks from the time the article is published).

New Weblog articles are posted on alonzofretwell.com every Monday morning.

Ubuntu Comprehensive Multimedia & Video Howto.