how can I rename multiple files by removing a character or string?

Question

As a follow-up to my previous question, if I have multiple files of the form

sw.ras.001
sw.ras.002
sw.ras.003
…

What command can I use to remove the ras. in the middle of all the files?

Answer 1

You can do this with a fairly small modification of either answer from the last question:

rename s/ras\.// sw.ras.*

or

for file in sw.ras.*; do
    mv "$file" "${file/ras./}"
done

Explanation:

rename is a perl script thattakes a perl regular expression and a list of files, applies the regex to each file's name in turn, and renames each file to the result of applying the regex. In our case, ras is matched literally and \. matches a literal . (as . alone indicates any character other than a newline), and it replaces that with nothing.

The for loop takes all files that start with sw.ras. (standard shell glob) and loops over them. ${var/search/replace} searches $var for search and replaces the first occurrence with replace, so ${file/ras./} returns $file with the first ras. removed. The command thus renames the file to the same name minus ras.. Note that with this search and replace, . is taken literally, not as a special character.

Answer 2

In any POSIX-compliant shell (bash, dash, ksh, etc):

for file in sw.ras.[[:digit:]][[:digit:]][[:digit:]]; do
    mv "${file}" "${file/ras\./}"
done

Or with rename:

rename 's/ras\.//' sw.ras.[[:digit:]][[:digit:]][[:digit:]]