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Full Discussion: use of sed over cat to merge files
Top Forums UNIX for Advanced & Expert Users use of sed over cat to merge files Post 302147777 by kahuna on Wednesday 28th of November 2007 12:23:56 PM
Old 11-28-2007
Quote:
Originally Posted by miwinter
I wondered if this could be achieved some way via sed instead
You could use sed, but

Quote:
surely it could be more efficient to insert the header (file 1) on the data file (file 2) and then just append the trailer (file 3) on the end.
it's not really more efficient. Sed still needs to read and write all of file 2 and needs to make checks on every line. Cat just needs to read and write, and can do so block by block rather than line by line.
 

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LEARN ABOUT DEBIAN

ppmtopgm

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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