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Full Discussion: shell scripting question
Top Forums UNIX for Dummies Questions & Answers shell scripting question Post 302526643 by uiop44 on Wednesday 1st of June 2011 05:55:26 AM
Old 06-01-2011
shell scripting question
Testing for the presence/absence of a pattern in a file, using /bin/sh:

Code:
while read a;
do
b="${a##*pattern*}";
[ "$b" = "" ];
done < file

This returns 0 if there's a match. That signal ($?) can then be used outside the loop.

However this method reads through the whole file, even if the match was found in, e.g., line 1.

Can we make it more like sed '/pattern/q' or grep -m1 "pattern"? That is, as soon as we have a match, stop.

How can we break out of the loop after the first successful match**, but still return a value that can be used outside the loop?

** Ideally, there will only ever be one match, because this script is in fact being used to prevent adding duplicate lines to a file.
 

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LEARN ABOUT REDHAT

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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