Learning the bash shell by Cameron Newham; Bill Rosenblatt

Author:Cameron Newham; Bill Rosenblatt
Language: eng
Format: mobi
Tags: Reference:Computers
ISBN: 9780596009656
Publisher: Beijing ; O'Reilly, 2005.
Published: 2009-02-09T00:00:00+00:00

eval $convert $filename $scale $border $standardise > $outfile

Now consider what happens when we don't want to scale the image. We do this:

scale=""

while getopts ":s:w:c:" opt; do

case $opt in

s ) scale=' | pnmscale' ;;

...

eval $convert $filename $scale $border $standardise > $outfile

In this code fragment, scale is set to a default of the empty string. If -s is not given on the command line, then the final line evaluates with $scale as the empty string and the pipeline will "collapse" into:

$convert $filename $border $standardise > $outfile

Using this principle, we can modify the previous version of the procimage script and produce a pipeline version. For each input file we need to construct and run a pipeline based upon the options given on the command line. Here is the new version:

# Set up the defaults

width=1

colour='-color grey'

usage="Usage: $0 [-s N] [-w N] [-c S] imagefile..."

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