Shell examples

1. List files and do a particular processing, e.g. convert or scale images

#!/bin/bash

# bash convert-images.sh ~/public/img/pains [-iname *.PNG]

directory=$1

args=${@:2:$#}

echo "arguments: $args"

count=0

for e in `find $directory $args`

do

if !(test -d $e)

then

echo "[$count] Processing file $e"

#e.g., rm $e

convert $e -resize 150 "$e.tmp"

mv "$e.tmp" $e

count=`expr $count + 1`

fi

done

2. Extract a specific column in a csv file

$awk -F, '{OFS=","; print $columnID}' INPUTFILE > OUPUTFILE

3. Compute diff between two files of items where each item is on one line, show what is file 2 but not in file 1