Shell Script Rename - linux

Question

Now I have the rename script like this:
cd /Users/KanZ/Desktop/Project/Test/
n=1
for file in *.jpg; do
echo $file
prefix=M
file_name=M$n.jpg
echo $file_name
n=$(( $n+1 ))
mv $file $file_name
done
The first if I run script, the all of jpg files will be M1.jpg M2.jpg M3.jpg but if I add the new file name A1.jpg to this directory and run script again. All of M1.jpg M2.jpg M3.jpg will be replaced by M4.jpg(before run script, this file named A1.jpg) because the first letter is A. It come before M. This is my problem. I would like to get M1 M2 M3 M4.jpg and every time if there are new files coming, this script will generate the continue name like M5.jpg M6.jpg . How is the code look like? Hope you understand that. Thank u for helping

Answer 1

The other answers given so far don't show you any good practice.
Here's one possibility that assumes that the numbering is continuous (i.e., no jump from M4.jpg to M6.jpg). Without that assumption, the script is safe (it won't overwrite existing files, but will not rename certain files).
#!/bin/bash
shopt -s extglob
shopt -s nullglob
cd /Users/KanZ/Desktop/Project/Test/
# Determine how many files MX.jpg you have (with X a number):
files=( M+([[:digit:]]).jpg )
n=${#files[#]}
for file in !(M+([[:digit:]])).jpg; do
file_name=M$((++n)).jpg
mv -vn -- "$file" "$file_name"
done
The -n option to mv: no clobber (do not overwrite an already existing file)
The -v option to mv: be verbose (so you don't need the echos you had)
The -- thing: end of options, only arguments will be found behind (just in case some files will start with a hyphen, that would confuse mv).

Answer 2

This little script will do it.
cd /Users/KanZ/Desktop/Project/Test/
n=$(ls -1 | grep '^M' -c) # find the number for M files
ls -1 *.jpg| grep -v '^M' | while read file # for each of the non-M files
do
n=$(($n+1));
new_file=M$n.jpg # new name with next available M file name
mv "$file" "$new_file" # rename with new file name
done
See how it works.
test/rename$ for x in 1 2 3; do echo A$x> A$x.jpg; done;
test/rename$ ls
A1.jpg A2.jpg A3.jpg
test/rename$ cat ../rnm.sh
#!/bin/bash
cd "$1"
n=$(ls -1 | grep '^M' -c)
nfiles=$(ls -1 *.jpg| grep -v '^M');
for file in $nfiles;
do
n=$(($n+1));
new_file=M$n.jpg
mv $file $new_file
done
test/rename$ bash ../rnm.sh ./
test/rename$ ls
M1.jpg M2.jpg M3.jpg
test/rename$ for x in 1 2 ; do echo B$x> B$x.jpg; done;
test/rename$ ls
B1.jpg B2.jpg M1.jpg M2.jpg M3.jpg
test/rename$ bash ../rnm.sh ./
test/rename$ ls
M1.jpg M2.jpg M3.jpg M4.jpg M5.jpg
test/rename$ for x in *.jpg; do echo $x; cat $x; done;
M1.jpg
A1
M2.jpg
A2
M3.jpg
A3
M4.jpg
B1
M5.jpg
B2

Answer 3

The way i understood your requirement is :
Change all the .jpg file names from what ever name they have to M*.jpg with an incremental number following M.
During multiple runs of the program the count should increase from the highest value of M file that was setup during the last run. For example if the first run of the program created M1, M2, M3 and then you add more files they should start from M4, M5, M6.
But the M1, M2, M3 itself should not be changed.
So a couple of suggestions :
you are setting n=1 at the start of the script. You should use the highest value of Mx.jpg that exists in the file from the previous run.
Second, when you are looking for files and iterating them, exclude all M*.jpg files, so that their names are not replaced.
Do you think this is your requirement. If you have any additional inputs please add a comment. Will send out the script in the next comment.
Test Cases :
Existing Files, X.jpg, ASG.jpg, GER.jpg
File names after the run : M1.jpg, M2.jpg, M3.jpg
If you just run the script once more after the first run with no additional files: There should not be any change in the file names : M1.jpg, M2.jpg, M3.jpg.
Now Add more files : Z.jpg, A.jpg, B.jpg
The file names should be changed as follows :
M1.jpg => M1.jpg, M2.jpg => M2.jpg, M3.jpg => M3.jpg, A.jpg => M4.jpg, B.jpg => M5.jpg, Z.jpg => M6.jpg.
So the file names will be M1.jpg, M2.jpg, M3.jpg, M4.jpg, M5.jpg, M6jpg.