Avoiding external utilities Post: 303010809

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Top Forums Shell Programming and Scripting Avoiding external utilities Post 303010809 by bakunin on Sunday 7th of January 2018 08:52:47 PM

01-07-2018

Registered User

Quote:

Originally Posted by SkySmart

nevertheless, here's what im trying to do to help me avoid external commands:

It is a good idea to avoid external utilities when possible, but that doesn't mean you should never use them. In fact they are quite good at what they are supposed to do and as long as you do not misuse them you are perfectly entitled to used them in your code.

In your case, where you search for a fixed string, you do not need egrepat all. egrep uses a very mighty (and therefore resource-intensive) regex machine, but to search for a fixed string you don't need that. Use fgrep ("fast grep"), which does the same as egrep but with a very limited (and hence resource-saving) regexp machine.

What you want to do cannot be done in shell. Actually it can be done, but not economically. It would look similar to this:

Code:

echo ${LongText} | while read line ; do
     case line in
          *RegexpA*)
               echo $line
               ;;

          *RegexpB*)
               echo $line
               ;;

     esac
done

I expect that to work slower than using (any) grep, though. echo, btw., is a shell builtin, if you use bash.

I hope this helps.

bakunin

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LEARN ABOUT LINUX

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)