Shell Programming and Scripting

Code:

APP=$2

while read line
do
   case $line in
     "$APP"*)
        group=${line%,*}
        perm=${line#*,}
        : do something here
        ;;
   esac
done < i_groups.txt

grp=$(echo "$line"|sed 's/^\(...\).*/\1/' )

It's an inefficient way of getting the first three characters of "$line".

The pattern between the first pair of slashes is the string to search for; it is replaced by the string after the second slash.

The parentheses delineate the first three characters and \1 selects that string.

It will not do what is wanted if the number of characters before the comma is anything other than 3.

A more efficient (and portable) method uses parameter expansion instead of an external command:

Code:

grp=${line%"${line#???}"}