Bash script for renaming of files

Question

I have several folders containing several video lectures. The names of the files(videos) are like topic blah blah blah - Lecture xx.mp4 I wish to rename them to Lecture xx.mp4

I have written the following bash script. And it appears to hang (gets slow), and doesn't give output also.

for file in *.mp4; do 
    echo "Renaming file :: $file"
    nn=$(grep -o 'Lecture.[0-9]*' "$file")
    echo $nn
    #mv "$file" "$nn"
done

Kindly help me to correct this script.

Answer 1

Your script searches the content of the file ( grep pattern [FILE...] ), when you actually want to change the $file parameter value. This should explain, why your command is slow and doesn't seem to work.

To change the value of the $file parameter, you can use a Bash feature called parameter expansions (see man bash ). In your case ${parameter##word} , that is remove matching prefix pattern , can be used. ${file##* - } will strip the longest match of * - . Note that * - is not a regular expression but a pattern. Pattern matching is different from regular expressions (compare * vs. .* ).

#!/usr/bin/bash

for file in *.mp4; do
  new=${file##* - }
  echo "Renaming '$file' to '$new'"
  #mv "$file" "$new"
done

Answer 2

You might find life easier using the rename program - it is a Perl script. In your case, you would do:

rename --dry-run 's/.*(Lecture \d+)/$1/' *mp4

Output

'topic blah blah blah Lecture 01.mp4' would be renamed to 'Lecture 01.mp4'
'topic blah blah blah Lecture 02.mp4' would be renamed to 'Lecture 02.mp4'
'topic blah blah blah Lecture 555556.mp4' would be renamed to 'Lecture 555556.mp4'

Then remove the --dry-run if you like what it says. It has the advantage over most ad-hoc shell scripts that it will not clobber files and you can do dry runs, and it supports the full Perl syntax so you can do very complicated things easily.