Puppy Linux Discussion Forum

[Bruce B]

Find scripts

You've already been introduced to; grep, redirection, variables.

Now, explaining command line variables. They are numbered from left to right as you type them. If you have three arguments, then you have variables $1 $2 $3

$@ means all command line arguments
$# means the number of arguments

In this example we use the case statement to determine which commands to run. And this is your first viewing of case in this study

The information we give case is $# which is the total count of our arguments. Valid matches, (true conditions), are 1 to 3. If we don't give case a number between 1 to 3 arguments, then * is true and it echos an error and does nothing.

Have a look and see what you can learn and derive.

[Bruce B]

tar and gzip

This chapter is short, sweet and important. I'll tell you why it's important. In the thousands of posts I've read on the forum, I seen many, many posts were it's obvious to me the problem is somewhere in the directory /etc

But I can't tell remotely exactly what the problem is.

/etc is not a static directory like /bin. /etc changes some every boot. Usually what brings on the users problem is a bad shutdown. Then, they can't recover.

Let's avoid problems by maintaining a backup of /etc

[Bruce B]

Change Directories - the cd command

The cd command is what we use to change directories. I'll start by offering some examples

cd : changes to the $HOME directory, for us it would be: /root

cd .. : takes us up one level

cd ../.. : takes us up two levels

cd /bin : takes us to /bin

cd bin : takes us to a child directory bin

cd /usr/bin : takes us to /usr/bin

bin : takes us to /root/bin - the reason why is, we made an alias called bin

cd - : returns us to our last directory

Related commands pushd and popd

pushd /usr/local/bin changes to /usr/local/bin and saves the directory we were in when we ran pushd

popd : returns to the the directory saved by pushd, 1x only

Adding extra commands

The uu command saves our current directory for the duration of the session or until we run uu again

The u command returns us to the directory saved by uu

The ad command displays the first level child directories, if any, of our current working directory.

The cdd command behaves like cd and shows all the first level subdirectories, if any.

The normal cd command used this way: cd /usr will change directories to /usr but not show the subdirectories in /usr

cdd /usr will change to /usr and show all the subdirectories in /usr/ This makes it easy to dig deeper with tab completion or copy and paste the output.

Adding the new commands;

[Bruce B]

Why?

In our last chapter, we made aliases, a function and installed a shell script. In this chapter I'll present theory for the whys of our whats.

Changing directories in a shell script

Remembering that our shell script is a child process, if we change directories in a script, we will change directories in the script. When the script is finished we are in the same directory we were in when when ran the script.

This script called usrbin;

#/bin/bash
cd /usr/bin

will actually do what it says, but when it finishes we are left in the same directory we ran it from.

Changing directories with an alias

This alias of the same name: usrbin

alias usrbin='cd /usr/bin'

Actually changes our current directory to /usr/bin, just as if we typed the commands. This alias doesn't launch a child process, thus giving the desired results.

What about the function?

We also added a function to .bashrc , I'll explain the rational for this now;

function cdd {
[ $1 ] && cd $1
ad
}

The function as an alias would look like this:

alias cdd='[$1] && cd $1 ; ad'

The problem with using an alias; is I've found aliases horrible for accepting command line arguments in the middle of the structure.

But they do great at the end of the structure, here's a working example;

alias mount='mount-FULL'

With this alias, when I use the command mount, on the command line, the actual mount command will be used, which in Puppy, and probably only Puppy is, mount-FULL

aliases accept appended arguments very well. Our problem is inserting them somewhere other than the end.

mount -t ext /dev/hda1 /mnt/hda1 , without an alias runs a Puppy shell script called mount which in turn will run mount-FULL and return to the parent shell when finished

With the alias

mount -t ext /dev/hda1 /mnt/hda1 runs the mount-FULL in the current shell

Why the shell script ad?

It works swell as a shell script, it lends itself well to shell scripting.

There nothing wrong with shell scripting. We will be doing a lot of shell scripting.

Major point: Sometimes there is a better approach to shell scripting, especially when trying to change directories in our current shell.

~

Chapter 18 - Why?

[Bruce B]

Troubles with whitespace

For our purposes; whitespace could be defined as characters which don't display.

Our most common text editor whitespace characters would be line endings, space and tab characters.

In bash we have the backslash \ character, an instructoion for the bash interpreter.

For this post I'll define \ as the 'do something different for the next character character'

In bash, the end of line (eol) character is the signal for end of command.

Sometimes I post code and have you insert the code, other times I don't post the code and have you download it.

Here is an excerpt from the file 'ad' in chapter 17

[Bruce B]

Teaching on a gradient - learning on your own

Many people associate learning with pain. I expect if you are even reading Chapter 21, you aren't one of these types of people. Or if you are, you have enough determinism and desire to learn not to let the pain association be a deterrent.

I love learning, but I really don't want anyone teaching me at a gradient too steep for me ( too painful ).

At this point of your learning experience, I'd like to state or restate, some of what I'm doing.

1) I'm trying to gradually help you set up a more friendly and powerful TUI environment than the one you started with. In doing this I might find myself a bit a cross-purposes with another objective, which is;

2) teaching bash scripting on an easy to learn gradient.

Obviously, I want you working in as friendly and powerful environment as possible. We build this environment gradually.

If you find some file unexplained and over your head, it is very possible, I'm trying to help with number (1). Explaining every aspect of a file may be on too steep a gradient for number (2), it might remain unexplained for this reason.

If you run into a situation like this, I advise; do not try and understand the file or procedure, if it is too hard, especially if stands to reason its purpose is in category number (1).

Two requisites defined for the bash programmer

1) Understanding the directory tree and files

2) File management skills

Two requisites explained

If you don't have a solid grasp of the directory tree and files, your file management skills will be lacking. Your programs will not be as expansive as they otherwise could be. Lots of what we might want to do in scripting pertains to file management.

Optional self-learning assignment

( Midnight Commander is a powerful file manager and just by using it, you will become gradually more familiar with Linux' directories and files. ) ( have you noticed with mc, you don't need to extract the .zip package and many other packages to copy files out of them? )

1) download the package tree.zip, its contents are one binary named tree and one text file called tree.txt which is the --help for tree.

At this point, no instructions should be needed. Simply put the binary file tree it it's appropriate directory and the documentation tree.txt in its appropriate directory.

2) using the Internet search, find a page which helps you to learn Linux default or basic directory tree. Read it and learn the basics, ( if you need the instructions at all ).

~

Chapter 21 - Teaching on a gradient - learning on your own

~

[Bruce B]

Formatting and colorizing text - a preview

This chapter is a preview for the next chapter, which will make very easy work of colorizing and formatting your script's on screen output.

Tastefully adding color to your text output, can add a professional look to your scripts.

When and where to color your text will be up to you.

Showing you how, and how to do it with ease, is my job.

See picture for preview.

~

Chapter 22 - Formatting and colorizing text - a preview

[Bruce B]

Displaying text with our scripts

The echo command is internal to our command processor, bash. How to know?

Type help and see if echo is in the list

In Puppy, the echo command may also be an external command. How to know?

which echo
and/or
ls -l /bin/echo

The rule is: an internal command will have precedence to an external one. However, if for some reason we wanted to use the external one we could, if it exists, by specifying the full path;

/bin/echo

Using echo

We typically use echo for displaying something to standard output (or in redirection). I want to emphasize echo's abilities go beyond what it is typically used for:

How about math? Try this command:

echo $[5+23]

Displaying files, try this:

echo *

Using quotes as a safety net

Until we learn the ins and outs and the peculiarities of echo, I recommend quoting what you wish to display. By quoting your intended output in your script, you are more likely to have the results you intended.

echo "My last directory was: $OLDPWD"

echo's default is to give a line feed at the end of the line. Remember from earlier the 'eol' is a non visible character, but it affects the formatting of our output.

echo -n says don't use a line feed. Let's try the above command with echo -n as follows;

echo -n "My last directory was: $OLDPWD"

echo -e : means enable interpretation of \ escape characters, which we need for coloring

Introducing cecho

If we type cecho on the command line, bash tells us:

cecho: command not found

Good, this is an available command name. We will call the our new command: cecho
It means; color echo

cecho usage:

cecho color "text for screen display"

for no new line;

cecho color "text for screen display" n

The cecho function, displayed in its present form, but I want to refine some things before you install it. The refinements and install instructions, will have to wait until next chapter. (or the next, next) Sorry. I'm starting to learn what they mean when saying, "Rome wasn't built in a day."

[Bruce B]

The case statement, escape sequences

[Bruce B]

A function based program

In this chapter we will work together and build a function based program. Programming begins with an idea. I have an idea that I would like you to be able to easily, very easily, as easy as possible make practice scripts.

I will title the program 'fun' and if that name doesn't suit you we will write it so you can change its title.

Scripts run commands. Scripts read from top to bottom. When I build a completely function based script, the first command is at the bottom. Putting it on the bottom means bash has read the entire script, (its functions) before any program execution begins.

The 'explanation formatting' in this chapter will be first the script, followed by explanation.

[Bruce B]

A conventionally formatted script (with explanations)

[Bruce B]

cecho

Package description:

[Bruce B]

hardinfo and lshw

I'd like to introduce you to some useful utilities in the next few chapters. In this chapter we will learn hardinfo and lshw

Instructions for hardinfo

cd /root/doc
hardinfo --generate-report --report-format html > hardinfo.html

Make it easy, copy and paste the long line to the command line. We learn through repetition, I'll repeat the copy and paste.

* Highlight the long line, leave it highlighted

* change to mrxvt

* to paste; shift insert or press middle mouse button, (hit enter) then; wait until hardinfo generates its report and performs its benchmarks, it takes some time.

Instructions for lshw

If you don't have lshw, download it from this post. You know the drill to install it. Then;

cd /root/doc
lshw -html > lshw.html

Remember the bookmark you made in your favorite browser? Open the directory /root/doc and view your new reports.

~

Chapter 28 - hardinfo and lshw

[Bruce B]

An unknown file type

I download a file referenced in this forum post: Slitaz' floppy boot disk boots Puppy

The file name is: floppy-grub4dos

Often when we download a floppy image, the extension is;

img : for floppy image ( sometimes hdd image )
or
imz : for bziped floppy image

There are no solid rules on the extension naming conventions with these images, just common conventions.

floppy-grub4dos has no extension - this is perfectly fine for me and for our lesson.

Learning more about the file

ls -l floppy-grub4dos

gives me this output:

-rw-r--r-- 1 root root 1474560 2009-07-06 00:51 floppy-grub4dos

The byte size 1474560 is precisely what one would expect for an uncompressed floppy image

file floppy-grub4dos, gives;

x86 boot sector, code offset 0x2e

hexedit floppy-grub4dos; for a visual interface

The boot sector, the first 512 bytes, doesn't look like a DOS boot sector. I think the floppy image is a Linux format.

Next I want to mount it and look at it in human readable form.

In order to mount floppy-grub4dos, a character device, we set it up on a block device, /dev/loop?

losetup -f : prints an available device

/dev/loop5, then the commands:

losetup /dev/loop5 floppy-grub4dos
mount -t ext2 /dev/loop /mnt/data

Note the file is mounted rw (read-write) we can modify it and save our changes. We cannot however increase the size.

The tree, in human readable form

|-- boot
| |-- btmgr.gz
| |-- etherboot
| |-- gpxe
| |-- memdisk
| |-- memtest
| |-- nssi.igz
| `-- plop.gz
|-- default
|-- grldr
|-- lost+found
|-- menu.lst
`-- slitaz.xpm.gz
2 directories, 11 files

umount /mnt/data
losetup -d /dev/loop5

Anthing learned?

Here is a list of the utilities you've been introduced to or reintroduced to in this chapter.

losetup
umount
mount
file
hexedit ( needs a better hex editor than what Puppy comes with )
ls

Optional assignment - You can do everything in this list.

~

Chapter 30 - an unknown file type

[Bruce B]

Black holes

For the purpose of this chapter, and not being an astronomer, I'll define a black hole as something that tends to absorb light. The light being your consciousness and the black hole being what tends to leave you in the dark.

In computing, I'd call the command line itself, a black hole for many. The Windows registry for others. Also the MBR.

I hope to shed some light on the MBR (Master Boot Record) in this chapter.

I've read forum topics where the OP had a bad MBR, or thought he had a bad MBR. Then from 10 to 30 or more follow up posts trying to help the OP.

On your partitioned hard disk your MBR will be the first physical sector of the hard disk.

Introducing dd - a copy / convert command.

Save a copy of the MBR:

dd if=/dev/hda of=hda.mbr bs=512 count=1

Restore the MBR from the copy:

boot to the command line
cd to the location of hda.mbr
the commands listed below are a bit more than necessary, but we really want to do this right or not at all.

sync
dd if=/dev/hda.mbr of=hda.mbr bs=512 count=1
sync
reboot

(sync flushes pending buffered writes held in memory)

Tips:

I can't tell you if it is /dev/hda, /dev/sda or something else, not with Puppy. Puppy changes. I can (later) tell you how to tell the Linux designation for your hard drive.

It is good to have a copy of your MBR. If the copy is of /dev/hda, it is best to save a copy on another device. The reason why is; if your hda MBR really goes bad, you may not even be able to access the drive to get to your backup MBR.

So, save it on a floppy disk, USB stick or some place other than hda. But also save it on /dev/hda because in most cases hda will be accessible and you can use the backup MBR from it.

Why the MBR goes bad

Usually, it never changes. It shouldn't ever change. But when we install various operating systems, we run the risk of it changing the MBR in a way we don't want to, or a dumb install routine changing it in way we really don't want. ( discounting the very unlikely event that our own stupidity isn't the cause )

When to save a copy of the MBR

Immediately after every time we modify our partitions. Especially primary partitions.

If you end up not deleting an earlier MBR, need to restore and become confused which backup to use, use the ls command like this:

ls -l <filename>

View the date and this will help determine the date of your backup, by reading the date in ls output - it should correspond with the date you partitioned.

We could also make dated backups. But we've not been introduced to the Linux date command yet.

Optional Assignment

Don't do the example exercises, (commands in blue), at this point.

Read http://en.wikipedia.org/wiki/Master_boot_record and learn a little more about the MBR, don't try and digest everything, too hard.

~

Chapter 31 - black holes