Generating a temp filename in Bash
Here's a function that simplifies the process of generating temporary filenames in shell scripts (I use bash). This function will generate a temporary filename given optional path and filename prefix parameters. If the file happens to already exist (a small chance), it recurses to try a new filename.
It doesn't cleanup temp files or anything fancy like that, but it does have the behaviour that if you never write to the temp file, it is not created. If you don't like that idea, touch the file before returning the name.
This procedure demonstrates the use of variable expansion modifiers to parse the parameters, and the $RANDOM builtin variable.
By default (with no parameters specified), this function will return a random filename in the /tmp directory:function gettmpfile()
{
local tmppath=${1:-/tmp}
local tmpfile=$2${2:+-}
tmpfile=$tmppath/$tmpfile$RANDOM$RANDOM.tmp
if [ -e $tmpfile ]
then
# if file already exists, recurse and try again
tmpfile=$(gettmpfile $1 $2)
fi
echo $tmpfile
}
[prompt]$ echo $(gettmpfile)
/tmp/324003570.tmp
If you specify a path and filename prefix, these are used to generate the name:
[prompt]$ echo $(gettmpfile /my_tmp_path app-tmpfile)
/my_tmp_path/app-tmpfile-276051579.tmp
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Why we love Tom
I just picked up my copy of Effective Oracle by Design to check some facts. It just took a few moments for it to remind me how much I enjoy and learn from Tom Kyte's work.
Why do we love Tom? I have a theory on this! It comes down to two factors:
- Substance. In an industry overwhelmed by candyfloss powerpoints, its refreshing to read someone who lives in the details, yet manages to retain sparkling clarity. It's apple pie for the technically oriented: database administrators, developers, and perhaps even a few architects(!).
- Uncompromising rigour. Never one to let an assumption go unchallenged or untested. If there was an IT version of MythBusters, he would be your Jamie to Dvorak's Adam (or vice versa if you like). Highly opinionated, his opinions are (annoyingly) based on hard facts. Sometimes you just want to jump on the keyboard and hack away to try and prove him wrong ... But that's good! He's got you thinking.
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Indexing with Oracle TDE
Oracle Transparent Data Encryption allows data encryption to be declared in a database schema, meaning that anything persisted on disk is protected from prying eyes.
It is a simple matter to setup TDE by bascially configuring a wallet location in sqlnet.ora, setting the key, and then opening the wallet after database startup. There's a good tutorial for this on OTN.
Declaring data encryption is then simply a matter of using the ENCRYPT keyword in your schema defintion, for example:
CREATE TABLE T1Indexing encrypted columns is covered in the Advanced Security Guide. It mentions specifically that you cannot create an index on a column that has been encrypted with salt (hence the 'NO SALT' above). There is another restriction that you cannot use encrypted columns in functional indexes, but I've yet to find this covered explicitly in the doco. You may be surprised to find out that this also means you get caught if you try to create an index with descending values, such as:
(SEQ NUMBER(15),
CCNUMBER CHAR(16) ENCRYPT USING 'AES128' NO SALT);
CREATE INDEX T1_AK1 ON T1 (CCNUMBER, SEQ DESC);
This will fail with the error "ORA-28337: the specified index may not be defined on an encrypted column". The reason for this is that the use of "descending" will be treated as a functional index.
Removing the "descending" qualifier allows a valid index to be built:
CREATE INDEX T1_AK2 ON T1 (CCNUMBER, SEQ);
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Exercising Regular Expressions and Arrays in Javascript
I've been working a bit with AJAX, and that soon prompted me to brush up on my Javascript. In the past I'd never used it to do more than a little validation or form "glue". Now revisiting the language from a true programmer's perspective, I recognise that it is pretty capable!
Speak Good Singlish! is a sample that gives regular expression and multi-dimensional array handling a good workout. It's a Singlish translator implemented in Javascript. I can't remember what sparked the idea to use this as an example, but somehow I got thinking back to ole "Jive" and "Valley girl" translators that have been floating around the net for many years.
The RegExp object usage in the sample is fairly standard, but the array handling is not.
I'm using a 2D array for the "lexicon" - basically a list of regex matches and replacements. For example the following fragment. You'll note that the second dimension can contain either a simple string or an array (as the replacement element):
var slexicon = [There's a core routine that iterates through the array and performs the substitutions. Where an array substitution is present, it uses a funtion inline to pick a random element from the array to perform the substitution:
[ '\\benglish\\b', 'Singlish' ] ,
[ '\\bdo\\b', [ 'do', 'do until sian', 'do sure can one' ] ]
];
// do the translationThe randomElement function is simplicity itself:
for (var i = 0; i < slexicon.length ; i++) {
var slexiconRow = slexicon[i];
var theRegex = new RegExp( slexiconRow[0], "gim" );
var theReplacement = slexiconRow[1];
if (theReplacement instanceof Array ) {
dataOut = dataOut.replace( theRegex, function (match) {return randomElement(theReplacement)} );
} else {
dataOut = dataOut.replace( theRegex, theReplacement );
}
}
// returns random element of an arrayThe HTML page contains the whole script inline, so it is easy to review in-place with a "view source". Enjoy!
var randomElement = new Function("x", "return x[Math.floor(Math.random() * (x.length))]");
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