Question

Consider that you want to rename all files of a given type (e.g. file extension) to a different filetype. For example, you want to change the file extension of all txt files to text. Write a shell script rename.sh (3%) that:

• takes two options as arguments. The first argument is the filetype you want to change. The second argument is the filetype you want to change files into.
• check that the two arguments are actually given. If not, the script is supposed to return a error message and terminate (0.5%).
• In the next step the script needs to find the corresponding filenames. Each file that is considered needs to be checked if it is a file (0.5%) and has read and write permissions (0.5%).
• Once files are found their file extensions need to change: For example, file.txt needs to change to file.text. HINT: check the man page of the command sed (1%).
• Finally, the script needs to output something to the effect of notifying the user that file.txt has been changed to file.text (0.5%).

Answer 1

Explanation :
1) Check for the no of arguments
if [ $# -ne 2 ];then                                                                                                                                   
echo "Provide two args [file 1: the original file] [file 2 : file name that the original file needs to be changed to]"                                                                                                                                 
exit 1                                                                                                                                                 
fi
checks for whether the no of args provided is atleast two or not
2) File Check : It checks whether the file to be renamed is present or not along with the extension check
Note : I have made check for only .txt
if [ -f "$file" ]                                                                                                                                      
then                                                                                                                                                   
if [ ${file: -4} == ".txt" ]                                                                                                                           
then                                                                                                                                                   
echo "file extension is .txt"                                                                                                                          
else                                                                                                                                                   
echo "file extension should be .txt only"                                                                                                              
fi                                                                                                                                                     
echo "$file found"                                                                                                                                     
else                                                                                                                                                   
echo "$file not found"                                                                                                                                 
exit 1                                                                                                                                                 
fi                                 
3) Check for Read and Write Permissions : The below code checks whether the file to be renamed has write and read permissions.
if [ -w $1 ] && W="Write"                                                                                                                              
then                                                                                                                                                   
echo "$file is having write permission"                                                                                                                
else                                                                                                                                                   
echo "$file is not having write permission"                                                                                                            
exit 1                                                                                                                                                 
fi                                                                                                                                                     
if [ -r $1 ] && R="Read"                                                                                                                               
then        
echo "$file is not having read permission"                                                                                                             
exit 1                                                                                                                                                 
fi                    
4) Renaming File using sed command
for filename in $1; do                                                                                                                             
newFilename=$(sed -E 's#img_([0-9]{1,2})-([0-9]{1,2})-([0-9]{1,2})_(.*)$#newyears_20\3-\2-\1_\4#' <<< "$2")                                          
mv "$1" "$newFilename"                                                                                                                               
echo "File has been renamed successfully"                                                                                                            
done   
Steps to be followed :
Step 1 : Open vi editor or any other editor based on the linux system you are using and copy the following content into the file rename.sh
if [ $# -ne 2 ];then                                                                                                                                   
echo "Provide two args [file 1: the original file] [file 2 : file name that the original file needs to be changed to]"                                                                                                                                
exit 1                                                                                                                                                 
fi                                                                                                                                                     
file=$1                                                                                                                                                
if [ -f "$file" ]                                                                                                                                      
then                                                                                                                                                   
if [ ${file: -4} == ".txt" ]                                                                                                                           
then                                                                                                                                                   
echo "file extension is .txt"                                                                                                                          
else                                                                                                                                                   
echo "file extension should be .txt only"                                                                                                              
fi                                                                                                                                                     
echo "$file found"                                                                                                                                     
else                                                                                                                                                   
echo "$file not found"                                                                                                                                 
exit 1                                                                                                                                                 
fi                                                                                                                                                     
if [ -w $1 ] && W="Write"                                                                                                                              
then                                                                                                                                                   
echo "$file is having write permission"                                                                                                                
else                                                                                                                                                   
echo "$file is not having write permission"                                                                                                            
exit 1                                                                                                                                                 
fi                                                                                                                                                     
if [ -r $1 ] && R="Read"                                                                                                                               
then        
echo "$file is not having read permission"                                                                                                             
exit 1                                                                                                                                                 
fi                                                                                                                                                     
for filename in $1; do                                                                                                                             
newFilename=$(sed -E 's#img_([0-9]{1,2})-([0-9]{1,2})-([0-9]{1,2})_(.*)$#newyears_20\3-\2-\1_\4#' <<< "$2")                                          
mv "$1" "$newFilename"                                                                                                                              
echo "File has been renamed successfully"                                                                                                            
done                                                                                                                                                               
Step 2 : execute the command ./rename.sh file.txt file.text
Step 3 : Kindly execute the above command for various test cases that is mentioned in the problem description.
Output:
sh-4.4$ ./rename.sh file.txt file.text                                                                                                                 
file extension is .txt                                                                                                                                 
file.txt found                                                                                                                                         
file.txt is having write permission                                                                                                                    
file.txt is having read permission                                                                                                                     
File has been renamed successfully                                                                                                                     
sh-4.4$ vi rename.sh