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Old 13th August 2017
gustaf gustaf is offline
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Default Visual guide to re_format(7)

Hello everyone!

I've finally gotten around to trying regular expressions.

For years, they seemed like magic incantations, accessible only to the initiated. There were too many incomprehensible details and I could never get them to work. It was easier to avoid them altogether and find a different solution to the problem.

This week, I hit a wall and couldn't avoid them anymore. There simply was no other easy solution. I cracked open the re_format(7) man page and decided to draw what I was reading. A diagram of the first few paragraphs emerged, then some tables that would make it easy for me to locate the RE components and their meanings.

The end result is a visual guide to OpenBSD re_format(7). I have posted this guide as a PDF attachment since I can't find a way to make a table with BBcode.

I think I finally have my facts straight about the OpenBSD implementation of regular expressions. If anyone sees any glaring (or not so glaring) inaccuracies, feel free to let me know.
Attached Files
File Type: pdf OBSD-Regular_Expressions.pdf (85.6 KB, 58 views)

Last edited by gustaf; 20th August 2017 at 03:16 PM. Reason: Changed title from 'Regular expressions in OpenBSD'
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Old 14th August 2017
gustaf gustaf is offline
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Under the BASIC REGULAR EXPRESSIONS section of the re_format(7) man page, there is a bulleted list of the ways basic regular expressions differ from extended regular expressions, one of which is:

Quote:
'*' is an ordinary character if it appears at the beginning of [a basic] RE or the beginning of a parenthesized subexpression (after a possible leading '^').
I don't see how this is different from the use of '*' in an extended RE.

Last edited by gustaf; 15th October 2017 at 08:04 PM.
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