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Full Discussion: How to check for Input Redirection in my script?
Top Forums Shell Programming and Scripting How to check for Input Redirection in my script? Post 302408499 by bakunin on Monday 29th of March 2010 04:40:42 PM
Old 03-29-2010
You could accept a specific option like "-f /path/to/inputfile" and act according to this option being set or not. Below is a sketch of the logic for better understanding. Use "getopts" instead of my construction for a production-grade script:

Code:
#! /bin/ksh

typeset inFile=""

while [ -n "$1" ] ; do
     case $1 in
          -f)
               shift
               inFile="$1"
               shift
               ;;

          -x)
               # some other option
               shift
               ;;

          *)
               print - "Error: unknown option"
               exit 1
               ;;

     esac
done

# if $inFile is empty the user has not specified any input file
if [ -n "$inFile" ] ; then
     # interactive operation goes here
else
     # batch operation goes here
fi

exit 0

Now "script -f /some/file" would lead to batch operation whereas "script" would lead to interactive operation.

I hope this helps.

bakunin
 

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LEARN ABOUT ULTRIX

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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