UNIX for Dummies Questions & Answers

Meaning of different operator.. This might help you to understand about %% and ##

Operator "#" means "delete from the left, to the first case of what follows."
         $ x="This is my test string."
 $ echo ${x#* }

is my test string.

Operator "##" means "delete from the left, to the last case of what follows."                   
$ x="This is my test string."
$ echo ${x##* }

string.
Operator "%" means "delete from the right, to the first case of what follows."
                     
$ x="This is my test string."
$ echo ${x% *}

This is my test

Operator "%%" means "delete from the right, to the last case of what follows."
                     
$ x="This is my test string."
$ echo ${x%% *}

This

file1='Jane Mid Doe.txt'
newfile='Jane.txt'
 
 
1) ext=${file1##*.}  
    ## delete from left to last match. so here pattern is '*.' so left to right last match will give txt. ( it deletes Jane Mid Doe. ). Now ext = txt

2) filename=${file%%.???} ( I think here its not file, its file1).
  %% right to left to last match. and ? matches single character
so filename will Jane Mid Doe

3) set -- $filename
This is to set the $filename as an environment. so you can access through  $1, $2.. variables.
now $1 - Jane , $2 - Mid  and $3 - Doe
4) newfile="1.$extension" 
so in this statement you have to change 1 to $1