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Top Forums Shell Programming and Scripting On how to select the right tool for a given task Post 302248046 by cfajohnson on Friday 17th of October 2008 12:37:29 AM
Old 10-17-2008
Quote:
Originally Posted by ghostdog74
i understand where you are coming from. but there are few situations i can think of that using shell provided internals are not suitable
1) writing portable scripts. The syntax that you use for string manipulations in bash for example, is not universal for every shell

The techniques I used are part of the standard UNIX shell.

They are portable to all modern *nix systems (and many older ones).

I used nothing that is bash specific.
Quote:
2) doing more complex string manipulation like grouped pattern matches.

When a regular expression, rather than wildcard expansion is necessary, then sed might be appropriate (though I would usually prefer awk).
Quote:
3) and of course, using sed to go over files can be faster than using pure shell constructs.

As I said, sed is for working with files.
 

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ppmtopgm(1)                                                   General Commands Manual                                                  ppmtopgm(1)

NAME
ppmtopgm - convert a portable pixmap into a portable graymap SYNOPSIS
ppmtopgm [ppmfile] DESCRIPTION
Reads a portable pixmap as input. Produces a portable graymap as output. The output is a "black and white" rendering of the original image, as in a black and white photograph. The quantization formula used is .299 r + .587 g + .114 b. Note that although there is a pgmtoppm program, it is not necessary for simple conversions from pgm to ppm , because any ppm program can read pgm (and pbm ) files automatically. pgmtoppm is for colorizing a pgm file. Also, see ppmtorgb3 for a different way of converting color to gray. And ppmdist generates a grayscale image from a color image, but in a way that makes it easy to differentiate the original colors, not necessarily a way that looks like a black and white photograph. QUOTE
Cold-hearted orb that rules the night Removes the colors from our sight Red is gray, and yellow white But we decide which is right And which is a quantization error. SEE ALSO
pgmtoppm(1),ppmtorgb3(1),rgb3toppm(1),ppmdist(1),ppm(5),pgm(5) AUTHOR
Copyright (C) 1989 by Jef Poskanzer. 10 April 2000 ppmtopgm(1)
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