The Windows 2000 command line feels an austere primitive when compared with the wonders of the UNIX/Linux equivalent. Windows XP feels a little better and PowerShell is another animal altogether. With the latter pair, you do get file or folder autocompletion upon hitting the TAB key. What I didn’t realise until recently was that continued tabbed cycled through the possibilities; I was hitting it once and retyping when I got the wrong folder or file. I stand corrected. With the shell in Linux/UNIX, you can get a listing of possibilities when you hit TAB for the second time and the first time only gives you completion as far as it can go with certainty; you’ll never get to the wrong place but you may not get anywhere at all. This works for bash but not ksh88 as far as I can see. It’s interesting how you can take two different approaches in order to reach the same end.
Archive for October, 2007
On numeric for loops in Korn shell scripting
The time hounoured syntax for a for loop in a UNIX script is what you see below and that is what works with the default shell in Sun’s Solaris UNIX operating system, ksh88.
for i in 1 2 3 4 5 6 7 8 9 10
do
if [[ -d dir$i ]]
then
:
else
mkdir dir$i
fi
done
There is a much nicer syntax supported syntax the advent of ksh93. It follows C language conventions found in all sorts of places like Java, Perl, PHP and so on. Here is an example:
for (( i=1; i<11; i++ ))
do
if [[ -d dir$i ]]
then
:
else
mkdir dir$i
fi
done
Detecting file ownership in Korn shell scripts
I recently was having a play with using a shell script to do some folder creation to help me set up a system for testing and I started to hit ownership issues that caused some shell script errors. At the time, I didn’t realise that there is a test that you can perform for ownership. The "-o" in the code below kicks in the test condition and avoids the error in question.
if [[ -o $dirname ]]
then
cd test
for i in 1 2 3 4 5 6 7 8 9 10
do
if [[ -d study$i ]]
then
:
else
mkdir study$i
fi
done
ls
cd ~
fi
Previously, I shared a way to test for directory (-d operator) and file (-f operator) existence that follows the above coding convention. However, there are a plethora of others and I have made a list of them here:
| Operator | Condition |
| -e file | File exists |
| -L file | File is symbolic link |
| -r file | User has read access to file |
| -s file | File is non-empty |
| -w file | User has write access to file |
| -x file | User has execute access to file |
| -G file | User’s effective group ID is the same as that of the file |
| file1 -nt file2 | File 1 is newer than file2 |
| file1 -ot file2 | File 1 is older than file2 |
| file1 -et file2 | File 1 was created at the same time as file2 |
It’s all useful stuff when you want to rid the command line output of errors in an above board sort of way. These are the kinds of things that often make life easier…
Negative logic in Korn shell scripts
I was looking for a way to negative logic, doing something when a condition is not satisfied, that is, and found that the way to do it is to do nothing when the condition is satisfied and something when it isn’t. Being used to saying do something when a condition is false, this does come as a surprise. It may be that I find another way on my UNIX shell scripting journey. In the meantime, the code below will only create a directory when it doesn’t already exist.
dirname=test
if [[ -d $dirname ]]
then
: # the colon operator means do nothing
else
mkdir test
fi
Changing the appearance of WordPress admin pages
There seems to be a percolation of plugins that aim to change the appearance of WordPress administration pages from their day-glow blue to something more pleasing; Earthtones is the one that I use for this blog but I have also been known to use WP Tiger Administration as well. Both options work well, though the latter needs some adjustments to work as well with WordPress 2.3 as it does with the 2.2 line. One area that they both fail to influence is the appearance of the upload screen. It doesn’t help that upload.php, the underlying PHP script, is a dual purpose animal: used in an iframe in the post editing page and standalone for upload management. Curiously, you can only upload files on the post editing page and not on the upload management screen, a definite quirk. The thing that really stops these admin theme plugins gaining any sort of purchase with upload.php is that it also uses an auxiliary stylesheet, upload.css, that is called after the WordPress function hook has been defined; if it came before this, then the styles in upload.css could be overridden. You could edit upload.php and edit the replacement stylesheet but the former activity would require repeating at every WordPress upgrade. I chose to edit upload.css and will keep that is a safe place so that I can replace the file following an upgrade. If upload.php was treated like every other admin script, then this would be unnecessary. A useful suggestion for Automattic, perhaps?
New FileZilla
I must admit that the release of FileZilla 3 passed me by until recently. From the user interface point of view, the changes don’t look too radical but it is now cross platform, a bonus for Linux and Mac users. It can also co-exist with FileZilla 2 for those Windows users needing features from that offering that aren’t yet available in FileZilla 3. That does pose the question: why upgrade when what you have works just as well? it just as well that transferring settings is as easy as importing the FileZilla 2 settings into its successor is as easy as importing an XML file: in version 3, go to Edit, then Import… on the menus and pick up the FileZilla.xml file from the installation directory for version 2. You might get some warnings and I certainly did but the FTP sites that I had set up already came over intact.