(OLD) (ARCHIVED) Puppy Linux Discussion Forum

Bruce B · Last edited by Bruce B on Mon 06 Jul 2009, 10:48; edited 1 time in total

Simple math

Sometimes we want to perform simple math on the command line;

add, divide, multiple, subtract - then have the command prompt return after the command.

Introducing the external command: bc

bc is an extremely powerful calculator - powerful enough just using it could become a study in and of itself

Introducing: shift

shift is an internal bash command. It moves the variable string from right to left. Here is an example:

args = these are my arguments

$1 : these
$2 : are
$3 : my
$4 : arguments

The 'shift' instruction makes this change

args = are my arguments

$1 : are
$2 : my
$3 : arguments

Note how $1 disappeared and the other arguments are re-designated right to left.

Bruce B

From image file to floppy disk

Don't do exercises in this chapter unless you want and have reason to do the exercises.

A floppy disk is a physical object which we cannot download. We can of course download a floppy image.

First thing to do after downloading the imagefile.img is check its size with the ls command, using the -l switch, like this:

ls -l imagefile.ext

If the size is 1474560, it's likely ready to use.

If it is smaller, then use file to learn more, maybe it's compressed with bzip2, or something else, file will tell you:

file imagefile.ext ; if output is;

bzip2 compressed data, . . .

There you have it, it needs to be decompressed prior to use

bzip2 -d imagefile.ext

Then, again;

ls -l imagefile.ext

If byte size is 1474560, this is the size we generally expect prior to copying to floppy.

You can run file again and see what file thinks of it

file imagefile.ext

We know the name of our image file, what's the name of our floppy device?

Considering how Puppy changes, I dare not say, lets see if we can learn from Puppy.

cat /etc/fstab ; if you see something like the line below, Puppy thinks your floppy is /dev/fd0, so that's what we will use.

Bruce B · Posted: Mon 06 Jul 2009, 10:42 Post subject: top Subject description: Chapter 34

Chapter 34 - top

Part of the curriculum in this series is introducing you to various command line utilities. In this chapter, I introduce you to top.

Assignment - open mrxvt and type top, then enter.

( q key to quit )

This is the end of your introduction to top. I have nothing to say about it, because there is something better.

htop

We will install a much more useful (yet quite small) utility called htop.

After you have installed htop, repeat the above assignment;

open mrxvt and type htop, then enter

It should be obvious to you why I've nothing to say about top and added htop.

I'll leave it to you to learn htop and read the text man page.

I do however . . .

. . . wish to teach you one aspect of htop, because it can get you out of trouble with a locked up application. And the technique described below is not particularly intuitive.

Suppose an application locks up and uses all available X resources. There is a GUI application somewhere in the menu to kill the offending application. But the GUI is so locked up, you cannot even access the menu.

I've seen posts where the Ctrl+Alt+Backspace key is the recommended way to leave X as if it were the standard way of operating Puppy. I cringe.

Left-Ctrl+Left-Alt+F2 will give you a terminal without crashing X or the application.

After logging in to your new terminal, run htop.

In htop, highlight the offending application. Then the F9 key, try and shutdown the offending application in this order;

15 SIGTERM

if that doesn't work, then;

9 SIGTERM

After closing the offending application, close htop and optionally logout of the terminal by typing exit.

Then;

Left-Ctrl+Left-Alt+F3 to return to your X session.

The instructions here probably won't have full meaning until you download and install htop.

Assignment - Please consider installing htop as highly recommend

~

Chapter 34 - top

Bruce B

Chapter 35 - Install Medit with Midnight Commander

In this chapter, we will practice using some Midnight Commander features. Also, install a great text editor / programmers editor called 'Medit'.

Medit isn't included with Puppy, but it is a part of its Official Repository.

We will do everything with Midnight Commander from downloading the medit archive to installing it.

Here are the steps:

If you do it right everything will be perfect, except your newly installed package will not be registered.

~

Chapter 35 - Install Medit with Midnight Commander . . .

. . . to be continued in Chapter 36

Bruce B · Posted: Mon 06 Jul 2009, 14:34 Post subject:

Chapter 36 - listing files contained in a pet archive

In Chapter 35 we installed medit-0.9.2.pet. We don't however have a listing of the files installed. Not yet anyway.

When we make scripts or aliases we want to give them meaningful names which are easy to remember.

Suppose I pick a name like listpetfiles, it's descriptive, but a little long.

If we use tab-completion, all we need do is type listp, then hit the tab key for the rest of the file name.

Well, we are going to call our next script listpetfiles, if you want a different name, you don't need to rename it at all.

Introducing ln - making symlinks

bin

ln -s listpetfiles showpetfiles

Introducing our script

Bruce B · Posted: Mon 06 Jul 2009, 15:38 Post subject:

Chapter 37 - Test your learning

Barry K wrote a very useful script called probepart, this is a utility all 'command line' Puppians should know about.

Also you want to know about a companion script probedisk

Usage:

probepart
probepart -m (for listing in megabytes)

Exercise:

Run probepart and see what it does

Open the probepart script and read it, it's well written and well commented. It's not too short and not too long. About 100 lines including comments and blanks. You won't be able to understand it completely, so don't expect yourself to.

Just see how much of it you do understand and the command portions you recognize, based on what you've learned so far.

Hint:

which probepart to locate the file

double click the which output, to select and copy to a clipboard

$guieditor (paste)

Note: in open source programming, we often share our work in a community with other programmers. Among other things 'commenting' is very important. We can often see what another programmer does, but without comments, we may not know why.

~

Chapter 37 - Test your learning

Bruce B

Chapter 38 - commenting your scripts

In this chapter we will make a script to mount an iso file. The emphasis here is commenting. I will over do the commenting beyond what most programmers would do. One reason I've not been commenting our scripts is because in the forum posting using the code function, I preserve the formatting but I can't control color. In this post we forsake the important indentation for the purpose of commenting. The comments are in gray and the commands are in green.

#!/bin/bash

# function main

main() {

# list of main's commands

var "$1"
mountiso "$1"
displayfile
umountiso

}

# function var

var() {

# check for arg1, if not, display message and exit

[ ! $1 ] && echo "Argument missing, exiting" && exit

# if arg1 is not a file name, show message and exit

[ ! -f $1 ] && echo "$1 doesn't exist" && exit

# get an available loop device

lodev=`losetup-FULL -f`

# check if an available loop device was found, by using exit code
# from grep, hide output, then check exit code

echo $lodev | grep /dev/loop >/dev/null
[ "$?" != "0" ] && echo "Problem finding available loop device" && exit

# define our mount point in a variable

mntpnt="/mnt/iso"

# does our mount point exist?
# if not make it

[ ! -d $mntpnt ] && mkdir $mntpnt

# last command in function, automatically returns to main for next command

}

# function mountiso

mountiso() {

# setup the iso file on the loop device

losetup-FULL $lodev "$1"

# mount the iso file

mount-FULL -t iso9660 -o ro $lodev $mntpnt

# function umountiso

umountiso() {

# this function occurs when mc closes, when mc closes
# mc returns to the directory it was opened from

# unmount the iso file

umount-FULL $mntpnt

# free the loop device

losetup -d $lodev

}

# function display file

displayfile() {

# using midnight commander
# code execution halts until mc is closed

mc $mntpnt

}

# call to main and pass $1 to main

main "$1"

This is far more detailed commenting than you are likely to use or encounter. But if code were commented as well as this, it would be a 'piece of cake' for the next programmer to pick it up and work with it.

I've attached the script to the post, including comments and indents. Please download it and open it with geany or medit. Either of these editors highlight syntax and you will see how easy it is to read the bash script with an editor of this type.

If you have a iso file to mount, run the script

mtiso <filename>

~

Chapter 38 - Commenting your scripts

Bruce B · Posted: Tue 07 Jul 2009, 05:52 Post subject:

Chapter 39 - mtsfs

In Chapter 38 we made a well commented script for easily mounting, viewing, working with and unmounting .iso files

The assignment for this chapter is:

Test mtiso and satisfy yourself it is a good script, if satisfied, use it as the template for making another script designed for mounting squashfs filesystems.

bin ( cd /root/bin )
cp mtiso mtsfs
$guieditor mtsfs &

make the necessary changes to the new file mtsfs

hint: the -t (type) parameter for an iso file is iso9660

the -t parameter for a .sfs archive is squashfs

~

Chapter 39 - mtsfs

Bruce B

Chapter 40 - Conditional expressions for integers

A lot of programming is about checking conditions. If this condition, we do this. It that condition we will do that. Or else we will do something different.

I think it's dawned on you by now, often times a programming routine simply makes a true or false check, as the basis for the decision what to do next.

Here I will introduce some basic bash math comparison operators

Bruce B · Posted: Thu 09 Jul 2009, 02:48 Post subject:

Chapter 43 - some common Linux compression utilities

bzip2
gzip
zip

I'm attaching a less common compression utility in this post, called lzma, you probably don't have it. I compressed it as a bzip2 file.

Download it, to unpack it;

Midnight Commander, this time use the menu F2 to, practice learning how it toggles compression and decompression on a bzip2 file

Destination is /root/bin

For a matter of interest: In most cases bzip2 compresses tighter than gzip.

I've found the Linux zip compresses about the same as gzip - but zip doesn't delete the target after compression.

lzma compresses tighter than any of the three aforementioned. So I want you to have lzma. And you will need it for the next chapter.

~

Chapter 43 - some common Linux compression utilities

Bruce B · Posted: Thu 09 Jul 2009, 03:06 Post subject:

Chapter 43 - Ispell

Ispell is an easy to use text interactive spell checker to enhance your GUI environment, making it even better than it already is.

To check a document ispell <filename>

To check spelling on a few words with keyboard input ispell

Some theory, about spell checkers.

You don't want the biggest dictionary for spell checking documents. A medium size dictionary is best because the big one has so many uncommon words, it might not flag a typo, if the typo happens to be spelled same as a rare word.

If you are good speller, a dictionary which doesn't make a lot of suggestions is also fine.

---------------

I compiled this spell checker to correspond with our directories.

Source file location was here: http://ficus-www.cs.ucla.edu/geoff/ispell.html

Should you prefer to do your own compile. The compile is easy, but there are some oddities, so read the documentation and think.

Installation of this package

mv ispell.tar.lzma.zip ispell.tar.lzma

forum won't allow the lzma extension, please consider this an exercise in frustration and I won't to it again.

lzma -d ispell.tar.lzma
tar xvf ispell.tar
install files according to the included README

Chapter 43 - Ispell

Bruce B

Chapter 44 - ls command

Sorry, no chapters the last few days, I've been down with the flu. These chapters require more of me than a serious flu allows. I think I'm back!

Here we go; I introduce the ls command. A very basic and essential command.

The ls command without switches will give you a sorted five column directory display of all your 'not-hidden' files and directories, providing you don't have names longer than 15 on a (typical) 80 column
display. ( did you catch that? )

ls will determine the number of sorted columns displayed by the longest file name or sub-directory name in the current.

With this understanding, you might want to limit the length of your files.

Using ls' switches, I'll introduce the ones we plan to use, but there are many more, to see them;

ls --help

Bruce B

Chapter 46 - user script an ls enhancement

lsf is short for ls find

lsf is a user made utility for finding files in your current directory by merely typing in portions of the file name. It accepts two arguments.

In /usr/bin lsf du gives us these possible files, because each file has the text string du

aseqdump*
db_dump*
du*
gsf-vba-dump*
gtk-query-immodules-2.0*
hexdump@
isodump*
objdump*
objdump86*
pango-querymodules*
pcprofiledump*
winedump*

lsf ^b gives: this list, because they all start with b
basename@
bc*
bcc*
bdftops*
bf_compact*
bf_copy*
bf_tar*
bison*
blinky*
blinkydelayed*
bochs*
bochs-dlx*
bogofilter*
bogolexer*
bogotune*
bogoupgrade*
bogoutil*
bxcommit*
bximage*
bzcmp@
bzdiff
bzegrep@
bzfgrep@
bzgrep*
bzip2recover*
bzless@
bzmore

lsf ^b c gives:

bc*
bcc*
bf_compact*
bf_copy*
bochs*
bochs-dlx*
bxcommit*
bzcmp@
bzip2recover*

( note @ means symlink , * means real executable file )

Here is lsf, the script

Bruce B · Posted: Mon 13 Jul 2009, 03:41 Post subject:

Chapter 47 - formatting output

A programmer or power user (you) should know the ls command quite well. Here is a bit more training

ls outputs in columns, sorted ascending down each column from left to right. If filenames are too long, we don't get as many columns. The column view shows a lot of files for the space used, but doesn't give many file details.

Bruce B · Posted: Mon 13 Jul 2009, 05:51 Post subject:

Chapter 48 - more formatting

Important Lectures and Theory

Basic categories of common and core utilities:

1) full version utilities

2) cut down utilities (which Puppy uses a lot of them

3) non-existent utilities - some scripting lessons you encounter will have you use an occasional utility which Puppy doesn't have. Not a problem, because you can troubleshoot it with the which command

4) utilities some scripting lessons won't let you use, because they don't trust you as root. Not a problem for us, is it?

------------------

Puppy has for all its history used many of the cut down versions of utilities. The reason why is obvious, to keep the distribution small by saving many megabytes over the larger utilities, man and info pages.

No, you cannot simply start replacing utilities on a one for one basis for the full versions.

The BusyBox utilities may not support the input switches and features we want. Just as important, they don't output exactly the same as the full versions, the predictive text formatting Puppy uses won't be right.

And by not using the BusyBox utilities in the right places, you can cause Puppy to make dumb decisions or even fail to boot.

Remember back to an earlier lesson about the PATH statement. Search left to right. We are at the end of the search for safety. If we put full featured utilities in our personal bin directory /root/bin, they will only be used if no match was found.

Here, I show you how to use full featured utilities in your personal directory with your personal scripts.

After finishing this lesson you will have three new full featured files:

/root/bin/tr
/root/bin/cut
/root/bin/head

In order for them to be used in the script, they need to be called by their full name. Our script's purpose is to find out how much physical memory your computer, (as if you didn't know already). Nevertheless, it will display it for you.

I'm calling the script mypc01, because I'd like to evolve it numerically, into something which gives even more useful information, and provides learning opportunities for you.

Let's look at the script.