Rename files using regular expression in linux

Edit: found a better way to list the files without using IFS and ls while still being sh compliant.

I would do a shell script for that:

#!/bin/sh
for file in *.srt; do
  if [ -e "$file" ]; then
    newname=`echo "$file" | sed 's/^.*\([0-9]\+\)x\([0-9]\+\).*$/S0\1E\2.srt/'`
    mv "$file" "$newname"
  fi
done

---

Previous script:

#!/bin/sh
IFS='
'
for file in `ls -1 *.srt`; do
  newname=`echo "$file" | sed 's/^.*\([0-9]\+\)x\([0-9]\+\).*$/S0\1E\2.srt/'`
  mv "$file" "$newname"
done

find + perl + xargs + mv

xargs -n2 makes it possible to print two arguments per line. When combined with Perl's print $_ (to print the $STDIN first), it makes for a powerful renaming tool.

find . -type f | perl -pe 'print $_; s/input/output/' | xargs -d "\n" -n2 mv

Results of perl -pe 'print $_; s/OldName/NewName/' | xargs -n2 end up being:

OldName1.ext    NewName1.ext
OldName2.ext    NewName2.ext
OldName3.ext    NewName3.ext
OldName4.ext    NewName4.ext

I did not have Perl's rename readily available on my system.

---

How does it work?

1. find . -type f outputs file paths (or file names...you control what gets processed by regex here!)
2. -p prints file paths that were processed by regex, -e executes inline script
3. print $_ prints the original file name first (independent of -p)
4. -d "\n" cuts the input by newline, instead of default space character
5. -n2 prints two elements per line
6. mv gets the input of the previous line

---

My preferred approach, albeit more advanced.

Let's say I want to rename all ".txt" files to be ".md" files:

find . -type f -printf '%P\0' | perl -0 -l0 -pe 'print $_; s/(.*)\.txt/$1\.md/' | xargs -0 -n 2 mv

The magic here is that each process in the pipeline supports the null byte (0x00) that is used as a delimiter as opposed to spaces or newlines. The first aforementioned method uses newlines as separators. Note that I tried to easily support find . without using subprocesses. Be careful here (you might want to check your output of find before you run in through a regular expression match, or worse, a destructive command like mv).

How it works (abridged to include only changes from above)

1. In find: -printf '%P\0' print only name of files without path followed by null byte. Adjust to your use case-whether matching filenames or entire paths.
2. In perl and xargs: -0 stdin delimiter is the null byte (rather than space)
3. In perl: -l0 stdout delimiter is the null byte (in octal 000)

You forgot a dot in front of the asterisk:

rename -n 's/(\w+) - (\d{1})x(\d{2}).*$/S0$2E$3\.srt/' *.srt

On OpenSUSE, RedHat, Gentoo you have to use Perl version of rename. This answer shows how to obtain it. On Arch, the package is called perl-rename.