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Mastering Regular Expressions, 3rd Edition by Jeffrey E.F. Friedl

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Chapter 1

If you have a TiVo, you already know the feeling!

“Regular expressions are easy!” A somewhat humorous comment about this: as Chapter 3 explains, the term regular expression originally comes from formal algebra. When people ask me what my book is about, the answer “regular expressions” draws a blank face if they are not already familiar with the concept. The Japanese word for regular expression, Image, means as little to the average Japanese as its English counterpart, but my reply in Japanese usually draws a bit more than a blank stare. You see, the “regular” part is unfortunately pronounced identically to a much more common word, a medical term for “reproductive organs.” You can only imagine what flashes through their minds until I explain!

The command shell is the part of the system that accepts your typed commands and actually executes the programs you request. With the shell I use, the single quotes serve to group the command argument, telling the shell not to pay too much attention to what’s inside. If I didn’t use them, the shell might think, for example, a ‘*’ that I intended to be part of the regular expression was really part of a filename pattern that it should interpret. I don’t want that to happen, so I use the quotes to “hide” the metacharacters from the shell. Windows users of COMMAND.COM or CMD.EXE should probably use double quotes instead.

Once, in fourth ...

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