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Full Discussion: Understanding regex behaviour when using quantifiers
Top Forums Shell Programming and Scripting Understanding regex behaviour when using quantifiers Post 302749561 by DGPickett on Friday 28th of December 2012 02:58:17 PM
Old 12-28-2012
Some flavors of regex have + for one or more, but you can just say 'ee*'. Also, there is '\{1,99\}' for 1 to 99 in the sed flavor. There must be about a dozen regex flavors, especially after the PERL guys dominated a POSIX version, so the word edge '\>' became '\b': Regex Tutorial - \b Word Boundaries

There are even schemes to make the * lazy as opposed to the normal greedy behavior. Consider the ksh/bash ${pathname##*/} is greedy, leaves just the entry name, but the ${pathname#*/} just removes the first slash and anything before it. This is not a standard regex, but I recall MULTICS qedx having a way to do the agressive/lazy switch back when. I wonder if regex are older than UNIX?

The g says how many times to apply the substitution: infinite. You can also say 3 to skip to the third match before substituting. It has to do with the writing, not the matching. With no flag, same as 1. http://www.regular-expressions.info/possessive.html
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LEARN ABOUT DEBIAN

ppmtosixel

ppmtosixel(1)						      General Commands Manual						     ppmtosixel(1)

NAME

       ppmtosixel - convert a portable pixmap into DEC sixel format

SYNOPSIS

       ppmtosixel [-raw] [-margin] [ppmfile]

DESCRIPTION

       Reads  a  portable  pixmap  as input.  Produces sixel commands (SIX) as output.	The output is formatted for color printing, e.g. for a DEC
       LJ250 color inkjet printer.

       If RGB values from the PPM file do not have maxval=100, the RGB values are rescaled.  A printer control header and a color assignment table
       begin the SIX file.  Image data is written in a compressed format by default.  A printer control footer ends the image file.

OPTIONS

       -raw   If  specified,  each  pixel  will  be explicitly described in the image file.  If -raw is not specified, output will default to com-
	      pressed format in which identical adjacent pixels are replaced by "repeat pixel" commands.  A raw file is often an order	of  magni-
	      tude larger than a compressed file and prints much slower.

       -margin
	      If  -margin  is not specified, the image will be start at the left margin (of the window, paper, or whatever).  If -margin is speci-
	      fied, a 1.5 inch left margin will offset the image.

PRINTING

       Generally, sixel files must reach the printer unfiltered.  Use the lpr -x option or cat filename > /dev/tty0?.

BUGS

       Upon rescaling, truncation of the least significant bits of RGB values may result in poor color conversion.  If the original PPM maxval was
       greater	than  100,  rescaling  also reduces the image depth.  While the actual RGB values from the ppm file are more or less retained, the
       color palette of the LJ250 may not match the colors on your screen.  This seems to be a printer limitation.

SEE ALSO

       ppm(5)

AUTHOR

       Copyright (C) 1991 by Rick Vinci.

								   26 April 1991						     ppmtosixel(1)
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