How to replace N repeated special characters in Bash?

Question

I want to replace any special character (not a number or letter) to one single '-'.

I tried the code below with some characters, but it doesn't work when the character is repeated more than 1 time because would still have more than one '-'.

#!/bin/bash
for f in *; do mv "$f" "${f// /-}"; done

for f in *; do mv "$f" "${f//_/-}"; done

for f in *; do mv "$f" "${f//-/-}"; done  

what I want:

test---file       ->  test-file

test   file       ->  test-file

test______file    ->  test-file

teeesst--ffile    ->  teeesst-ffile

test555----file__ ->  test555-file

Please, explain your answer because I don't know much about bash, regexp...

Answer 1

There are a couple of different rename (or prename ) commands available in various distributions of Linux what will handle regex substitutions.

But you can also use Bash's extended globbing to do some of that. The pattern ${var//+([-_ ])/-} says to replace any runs of one or more characters that are listed in the square brackets with one hyphen.

shopt -s extglob
# demonstration:
for file in test---file 'test   file' test______file teeesst--ffile test555----file__
do
    echo "${file//+([-_ ])/-}"
done

Output:

test-file
test-file
test-file
teeesst-ffile
test555-file-

The extended glob +() is similar to .+ in regex. Other Bash extended globs (from man bash ):

          ?(pattern-list)
                 Matches zero or one occurrence of the given patterns
          *(pattern-list)
                 Matches zero or more occurrences of the given patterns
          +(pattern-list)
                 Matches one or more occurrences of the given patterns
          @(pattern-list)
                 Matches one of the given patterns
          !(pattern-list)
                 Matches anything except one of the given patterns

Note that the final hyphen is not removed here, but could be using an additional parameter expansion:

file=${file/%-/}

which says to remove a hyphen at the end of the string.

Answer 2

You can use tr (as shown above in the comment) or, actually, sed makes more sense in this case. For example, given your list of filenames:

$ cat fnames
test---file
test   file
test______file
teeesst--ffile
test555----file__

You can use the sed expression:

sed -e 's/[[:punct:] ][[:punct:] ]*/-/' -e 's/[[:punct:] ]*$//'

Example Use/Output

$ sed -e 's/[[:punct:] ][[:punct:] ]*/-/' -e 's/[[:punct:] ]*$//' fnames
test-file
test-file
test-file
teeesst-ffile
test555-file

Depending on how your filenames are stored, you can either use command substitution individually, or you can use process substitution and feed the updated names into a while loop or something similar.