Technology Tales

Twin-pane Windows file managers

When Microsoft moved away from its two pane file manager with the advent of Windows 95, I was one of those who thought it to be a retrograde step. While two Windows Explorer instances can be tiled on a desktop, the old two-pane paradigm still has its uses and there are third party purveyors of such things. Salamander from ALTAP is one such option, as is SpeedProject's SpeedCommander. While I have been using the latter for most of a year now and would gladly pay for it but for the fact that SpeedProject's payment system isn't working. It's just as well that the demo continues to function fully following the expiry of its evaluation period. It even takes the twin pane paradigm further by adding sub-panes within each of these, but that isn't all to this major update to the Norton Commander concept. Recently, I downloaded the free version of Salamander to have a look and, though basic, it does a lot of what I ask of it, so I might continue to see how it performs and may even evaluate the commercial version to see how it goes.

Updating Oracle data tables that have associated sequence objects

Here’s something that I want to put somewhere for future reference before I forget it: keep sequences associated with Oracle data tables up to date while adding records. Given that it took me a while to find it, it might come in useful for someone else too.

The first thing is to update the sequence itself:

SELECT TABLE_SEQ.NEXTVAL FROM DUAL;

Dual is a handy single record table that you can use to update sequences. Use the actual associated table itself if you like to see that sequence number rocket…

The next thing is to use the new value to assign a table ID as part of an INSERT statement:

INSERT INTO “TABLE” VALUES (TABLE_SEQ.CURRVAL, 1, ‘Test value’);

Quoted strings in Oracle SQL

Here's a gotcha that caught up with me on my journey into the world of Oracle SQL: string quoting. Anything enclosed in double-quotes (") is the name of an Oracle object (variable, table and so on) while values are enclosed in single quotes ('). The reason that this one caught me out is that I have a preference for double quotes because of my SAS programming background; SAS macro variables resolve only when enclosed in double-quotes, hence the convention.

WordPress.com and user registration

Uses for symbolic links

UNIX (and Linux) does a wonderful trick with its file and folder shortcuts; it effectively treats them as file and folder transporters that transfer associate a file or folder that exists in one folder hierarchy with another, and it is treated as if it exists in that hierarchy too. For example, the folder named images under /www/htdocs/blog can have a link under /www/htdocs/ that makes it appear that its contents exist in both places without any file duplication. For instance, the pwd command cannot tell a folder from a folder shortcut. To achieve this, I use what are called symbolic links and the following command achieves the outcome in the example:

ln -s /www/htdocs/blog/images /www/htdocs/images

The first file path is the destination for the link, while the second one is that for the link itself. Once, I had a problem with Google Reader not showing up images in its feed displays, so symbolic links rode to the rescue as they did for resolving a similar conundrum that I was encountering when editing posts in my hillwalking blog.

Checking existence of files and directories on UNIX using shell scripting

Having had a UNIX shell script attempt to copy a non-existent file, I decided to take another look for ways to test the existence of a file. For directory existence checking, I was testing for the return code from the cd command, and I suppose that the ls command might help for files. However, I did find a better way:

if [ -f $filename ]
then
    echo "This filename [$filename] exists"
elif [ -d $dirname ]
then
    echo "This dirname [$dirname] exists"
else
    echo "Neither [$dirname] or [$filename] exist"
fi

The -d and -f flags within the evaluation expressions test for the existence of directories and files, respectively. One gotcha is that those spaces within the brackets are important too, but it is a very way of doing what I wanted.

Google Reader

Going through the stats for my other blog, I noticed some activity from Google Reader and decided to investigate. What I discovered was a very capable feed reader, much better than Technorati's equivalent. The interface feels a little like an email client, with a different entry in the sidebar for each feed. It also gives you full text and pictures for each blog article that it picks up, though it messes with my hillwalking blog for some reason... As a feed aggregator, it performs very well and makes my blog surveying a lot more effortless. I know that Outlook 2007 has aggregation functionality too, but the portability of Google's little online offering makes it worth taking further, especially as you wouldn't need to pay for it anyway.

Update: Google Reader also allows you to share items from your feeds.

Learning about Oracle

Oracle SQL Developer and MySQL

Because of my work, I recently have had a bit of exposure to Oracle SQL Developer, which I have been using as part of application development and testing activities. For further investigation, I decided to have a copy at home for further perusal (it's a free download) and it was with some interest that I found out that it could access MySQL databases. To accomplish this, you need Connector/J for MySQL so that communication can occur between the two. Though you quickly notice the differences in feature sets between Oracle and MySQL, it seems a good tool for exploring MySQL data tables and issuing queries.

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