Saturday, October 27, 2007

More on bash, arrays, and index values

So, if you "man bash", you will see the following:
Arrays
Bash provides one-dimensional array variables. Any variable may be
used as an array; the declare builtin will explicitly declare an array.
There is no maximum limit on the size of an array, nor any requirement
that members be indexed or assigned contiguously. Arrays are indexed
using integers and are zero-based.
...
Any element of an array may be referenced using ${name[subscript]}.
...
${#name[subscript]} expands to the length of ${name[subscript]}. If subscript is * or @,
the expansion is the number of elements in the array.
...
The unset builtin is used to destroy arrays. unset name[subscript]
destroys the array element at index subscript. unset name, where name
is an array, or unset name[subscript], where subscript is * or @,
removes the entire array.
What does all that mean? It means that index values don't get reset when you unset array elements, so you shouldn't rely on ${#name[*]} in loops, unless you know that the index values are contiguous. So, if you want to loop based on the number of elements, you had better reset the index values by using something like: name=(`echo ${name[*]}`)

Copy and paste the following into a file, and then run it using your favorite implementation of bash (Cygwin, OS X, Linux, BSD, etc.) to see how it all works:
#!/bin/bash
function show_array {
echo There are ${#NUMBERS[*]} numbers in the array.
echo The index positions and values are:
IDX=0
while [ $IDX -lt ${#NUMBERS[*]} ]; do
echo -e $IDX \\t ${NUMBERS[$IDX]}
let IDX+=1
done
}
function pause () {
read -p "$*"
}
echo Bash Shell Array Element Index Handling
echo ----------------------------------------
NUMBERS=(zero one two three four five six seven eight nine)
show_array
pause "Press Enter "
echo ----
echo Now, let\'s unset number five, and see what happens...
unset NUMBERS[5]
show_array
echo Eek!, looks like there\'s a NULL element in there.
echo So, the number of elements has been reset, but the indexing has not.
echo Indexing is non-contiguous by design, so this isn\'t a bug. However,
echo this means that we do not get to see all of the elements if we are
echo looping based on the number of elements in the array.
pause "Press Enter "
echo ----
echo Let\'s try to unset number 1 this time...
unset NUMBERS[1]
show_array
echo Looks like there\'s another NULL element in there, now.
echo Again, the number of elements has been reset, but the indexing has not...
echo The \${#NUMBERS[*]} does not count NULLs, but index values do not
echo change. The while loop produces apparent garbage after some elements
echo have been unset.
pause "Press Enter "
echo ----
echo Enter the cheesy work-around:
echo "It looks like this: NUMBERS=(\`echo \${NUMBERS[*]}\`)"
echo This kills the NULL values and resets the indexing so it is
echo contiguous again...
NUMBERS=(`echo ${NUMBERS[*]}`)
show_array
Happy bash-ing...

Friday, October 26, 2007

GPG Extension for Firefox!

FireGPG is a Firefox browser extension that can handle crypto tasks. I'm going to have to try to integrate this with my "Portable Apps" install of Firefox so that I can use crypto on Gmail and Hotmail from anywhere... Looking forward to trying it out this evening!

Update: Seems to work just fine -- both for encrypting and decrypting. I had to over-ride the default keychain location for GPG and the default GPG location for the extension... Will need to try from a different machine to be completely sure, but I think I've nailed it!

Saturday, October 20, 2007

Rejected Ubuntu Release Names

As I pointed out previously, Ubuntu Releases have all been alliterative animal phrases. While the initial two releases were "Warty Warthog," and "Hoary Hedgehog," the adjectives in these phrases have become somewhat more flattering since, featuring: Breezy, Dapper, Edgy, Feisty, and (currently) Gutsy. With this trend in mind, it is fun to imagine some of the submissions that may have been received and rejected by the Ubuntu team. I submit the following alphabetically-aligned alliterative adjective/animal amalgamations that are unlikely to ever be associated with any project or product:

  • Acrid Amoeba
  • Bald Beaver
  • Cantankerous Cub
  • Devilish Dromedary
  • Evil Elk
  • Fearsome Frog
  • Geriatric Grunion
  • Heinous Hippo
  • Illiterate Ibis
  • Jacobite Joey
  • Killer Kite
  • Lame Llama
  • Mongoloid Mongoose
  • Noisome Nit
  • Onerous Orangutan
  • Precarious Porpoise
  • Queer Quokka
  • Rabid Rat
  • Sterile Serpent
  • Twisted Trout
  • Urbane Ungulate
  • Voluptuous Vixen
  • Warlike Walrus
  • Xenophobic "X-animal"
  • Yucky Yak
  • Zero-sum Zebrafish

Friday, October 19, 2007

Virtual Gutsy

Updated my Ubuntu 7.04 (Feisty Fawn) virtual machine to 7.10 (Gutsy Gibbon) -- nice and smooth via the network install. Since it's in a VM, I don't see the fancy 3D interface elements. C'est la vie...

In other Ubuntu news, the next version has already been given a name (Hardy Heron). I would like to be the first to propose the following properly alliterative animals for future versions:
  • Intrepid Iguana
  • Jocund Jackal
  • Kinetic Kangaroo
  • Lively Lemur
  • Merry Marmot
  • Nifty Newt
  • Obliging Ocelot
  • Puissant Puma
  • Quintessential Quail
  • Robust Raccoon
That ought to last a couple of years...

Wednesday, October 17, 2007

Monday, October 15, 2007

Array Variables in bash

In my efforts to improve my NTFS-3G mount/re-mount script, I had to learn how to implement an array variable. Turns out it's painfully simple, and now I feel that I should go back and eradicate the evil temporary files that I used in some of my earlier quickly-generated scripts. But, I digress... Here are some quick basics that proved useful:
  • Array variables can be implicitly declared, e.g. PETS=(dog cat bird fish) builds a four-element array.
  • To show the whole array, use ${PETS[*]}
  • To show the number of elements in the array, use ${#PETS[*]}
  • Element index starts at zero so ${PETS[1]} will return cat
Here's the sample code that I threw together to make sure I figured it out properly, with comments added in a different font to explain each line of the script:
#!/bin/bash
# build an array of partitions (OS X), populated only with disk#s# for each partition
TEST=(`diskutil list | egrep disk.s. | awk '{print $NF}'`)
PARTS=0
# Build a menu that shows each partition in the array
# but start numbering at 1 instead of 0
while [ $PARTS -lt ${#TEST[*]} ]; do
let COUNT=PARTS+1
echo "$COUNT".\) ${TEST[$PARTS]}
let PARTS+=1
done
# Prompt for / grab user input, and see if it matches something on the menu
echo -n Please select a partition from the menu above:
read TRYIT
case $TRYIT in
[1-${#TEST[*]}])
# NOTE: [1-3]is an expression that matches 1, 2, or 3...
echo You typed a valid number: $TRYIT;;
*)
echo You typed a bad number: $TRYIT;
exit 100; # set a non-zero exit code
esac

Sunday, October 14, 2007

Photo Map Updates

Added a few gallery links to my (Google) photo map:
  • Glacier National Park (Placemark @ Logan Pass)
  • Saint Louis (Placemark @ The Gateway Arch)
  • West Virginia (Placemark @ The New River Gorge Bridge)

NTFS-3G Mount/Re-Mount Script for OS X

Requirements:
Features:
  • Optional Command-Line Parameters:
    • Partition to mount or re-mount (must be specified as the first parameter)
    • Use the force option at mount (can be specified as either first or 2nd parameter)
    • If no parameters are entered, script enters "interactive mode," and prompts user with a menu of confirmed NTFS partitions
  • Handle volumes that are currently using the (read-only) kernel NTFS driver
    • Prompt to unmount, custom exit level if user-aborted
    • Capture name that is assigned in Finder
    • Remount as read/write using the same Finder name
  • Handle volumes that are not currently mounted
    • Mount and assign a default Finder name: NTFS-disk#s#
  • Input Sanitizing
    • Volumes can be entered as "/dev/disk#s#" or (preferably) as "disk#s#"
    • Script throws custom exit level if volume does not exist
    • Script throws custom exit level if mount command fails due to non-NTFS volume
    • Script throws custom exit level if it encounters NTFS-3G errors during mount
  • (Possible Future Enhancements)
    • Add a -? or --help option to the script for ├╝ber-completeness
    • Silent output -- rely only on the exit codes (Why? -- I can always redirect to /dev/null if I want to call it from within another script)
    • Something I haven't thought of yet...
  • bzip2 compressed version of the script (now includes updates through 1.4).
UPDATES
[Oct. 15] Version 1.1:
  • Implemented volume-unique mount points, so more than one disk can be mounted
  • Implemented menu (via array variable) for volume selection -- type a number instead of having to type disk#s#
[Oct. 16] Version 1.2:
  • Implemented actual type detection using File System field from "diskutil info disk#s#"
  • Previous method used reasonable speculation based on type field from "diskutil list"
  • Learned that array index values can be non-contiguous, and are not changed when array elements are unset. (This led to a later post.)
[Oct. 19] Version 1.3:
  • Added current mount point information to menu (yep, another array)
  • Added header bar to menu
  • Added Quit option to menu
[Oct. 27] Version 1.4:
  • Implemented the file system type detection for volumes that are input from the command line.
  • Previously, this was only implemented for volumes on the menu in "interactive mode."
  • Added an exit level for "Not an NTFS Volume."

Thursday, October 11, 2007