Showing results for May 2006 - Page 2 of 4 - The Old New Thing

May 22, 2006
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How do I write a regular expression that matches an IPv4 dotted address?

Raymond Chen
Raymond Chen

Writing a regular expression that matches an IPv4 dotted address is either easy or hard, depending on how good a job you want to do. In fact, to make things easier, let's match only the decimal dotted notation, leaving out the hexadecimal variant, as well as the non-dotted variants. For the purpose of this discussion, I'll restrict myself to the...

Code
May 19, 2006
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Raymond 1, Sidewalk 1

Raymond Chen
Raymond Chen

I successfully avoided the stealth sidewalk the other day. This evens the score. (Today is Starbucks Bike to Work Day.)

Non-Computer
May 19, 2006
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Redirecting output can result in altered program behavior

Raymond Chen
Raymond Chen

Consider a program whose output to the console goes like this. (I've prefixed each line with the output stream.) You want to capture both the normal and error streams, so you run the program and append "" to capture both streams into a single file. But when you look at the resulting output file, you get this: What happened? Most programs c...

Code
May 18, 2006
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Making up new Winter Olympic events

Raymond Chen
Raymond Chen

My approach to inventing new Winter Olympic events is to create new opportunities for head-to-head competition, opening the door to new dramatic possibilities. For example, in Ski Jump Biathlon, one team jumps while the other team tries to shoot them (with paint pellets, of course) as they sail through the air. In Figure Curling, one team perform...

Non-Computer
May 18, 2006
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The redirection operator can occur in the middle of the command line

Raymond Chen
Raymond Chen

Although the redirection operator traditionally appears at the end of a command line, there is no requirement that it do so. All of these commands are equivalent: All of them echo "A B" to the file "C". You can use this trick to avoid the redirection problem we discussed last time. We saw that writing inadvertently interprets the "2" as p...

Tips/Support
May 17, 2006
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Don't mention the war. I mentioned it once, but I think I got away with it all right

Raymond Chen
Raymond Chen

The Germans is probably the most well-known episode of Fawlty Towers. Who better than John Cleese, therefore, to release the song Don't Mention the War, just in time for the World Cup. The purpose is to mend fences between Britain and Germany, but it might just make things worse, who knows.

Non-Computer
May 17, 2006
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Beware of digits before the redirection operator

Raymond Chen
Raymond Chen

If you want to put the string "Meet at 2" into the file "schedule", you might be tempted to use If you try this, however, you'll see the string "Meet at" on the screen and the "schedule" file will be blank. [Typo fixed, 10am] What happened? A digit immediately before a redirection operator modifies which stream the redirection operator appl...

Tips/Support
May 16, 2006
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Command line redirection is performed by the command line interpreter

Raymond Chen
Raymond Chen

The magic characters like <, >, and | in command lines like are interpreted by the command interpreter ; they aren't built into the function. (This is obvious if you think about it. That command line created two processes; which one should return a handle to?) If you pass a command line like this to , it will merely run the program w...

Tips/Support
May 15, 2006
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The first word on the command line is the program name only by convention

Raymond Chen
Raymond Chen

The format of the command line returned by is "", but this is only a convention. If you pass for the to the function, then the function will treat the first word of the as the program name. However, if you pass a value for , then that string determines the program that is run, and the string passed as the is not used for that purpose. This ...

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