try this:

key=key.replace(/ /g,"_");

that'll do a global find/replace

javascript replace

Regular expressions are not a tool to replace texts inside strings but just something that can search for patterns inside strings. You need to provide a context of a programming language to have your solution.

I can tell you that the regex _ will match the underscore but nothing more.

For example in Groovy you would do something like:

"This_is_my_name".replaceAll(/_/," ")
    ===> This is my name

but this is just language specific (replaceAll method)..

Provided that your tags are all images, with a similar format to the tags above you can acomplish this in a single regular expression using positive and negative lookaheads.

\s(?=(\w+))(?!style|alt|src|\d+px)

Positive Lookahead

The first step in this regular expression is to find spaces followed by one or more alphanumeric characters.

\s(?=(\w+))

This expression will find following matches:

• Space between "img" and "style"
• Space between "width" and "800px"
• Space before src
• Spaces in the filename
• Space between filename and alt

The outer brackets allow of this regexp mean that the resulting matches will feed into the next portion of the expression i.e. the negative lookahead.

Negative Lookahead

This step negates the matches we are not interested in:

(?!style|alt|src|\d+px)

Another alternative, would be to use two positive lookaheads. This approach would give you a final regexp which looks like this:

\s(?=(\w+))(?=\w+(\s|\w)*\.[jpg])

The first portion of this expression is the same as above. The second lookahead is a bit more generic, looking for an alphanumeric character to start, followed by more alphanumeric characters or spaces multiple times followed by the .jpg extension.

Second Positive Lookahead

(?=\w+(\s|\w)*\.[jpg])

IDK if rename can work recursively. I made some empty files with space(s) in their names inside a subdirectory without a space and one with. The below works for me to rename files with one or more spaces in their names with one underscore, and doesn't bother the subdirectory with spaces in its name.

root@server <1>: /cwd# mkdir subdir1 'sub dir 2' ; touch 'subdir1/file 1' 'sub dir 2/file  2  ' 'subdir1/ f i l e 3 ' 'sub dir 2/   f  i  l  e   4   '

root@server <2>: /cwd# ls -lhR
.:
total 0
drwxr-xr-x 2 root root 80 Dec 28 00:42  subdir1
drwxr-xr-x 2 root root 80 Dec 28 00:42 'sub dir 2'

./subdir1:
total 0
-rw-r--r-- 1 root root 0 Dec 28 00:42 'file 1'
-rw-r--r-- 1 root root 0 Dec 28 00:42 ' f i l e 3 '

'./sub dir 2':
total 0
-rw-r--r-- 1 root root 0 Dec 28 00:42 'file  2  '
-rw-r--r-- 1 root root 0 Dec 28 00:42 '   f  i  l  e   4   '

root@server <3>: /cwd# find . -type f -exec echo {} \; | tee ../FILES.txt
./sub dir 2/   f  i  l  e   4
./sub dir 2/file  2
./subdir1/ f i l e 3
./subdir1/file 1

root@server <4>: /cwd# while IFS= read line ; do
> dirname="${line%/*}"
> fn=${line##*/}
> fn="${fn//+( )/_}"
> mv -v "$line" "${dirname}/${fn}"
> done < ../FILES.txt
renamed './sub dir 2/   f  i  l  e   4   ' -> './sub dir 2/_f_i_l_e_4_'
renamed './sub dir 2/file  2  ' -> './sub dir 2/file_2_'
renamed './subdir1/ f i l e 3 ' -> './subdir1/_f_i_l_e_3_'
renamed './subdir1/file 1' -> './subdir1/file_1'

root@server <5>: /cwd# ls -lhR
.:
total 0
drwxr-xr-x 2 root root 80 Dec 28 00:42  subdir1
drwxr-xr-x 2 root root 80 Dec 28 00:42 'sub dir 2'

./subdir1:
total 0
-rw-r--r-- 1 root root 0 Dec 28 00:42 file_1
-rw-r--r-- 1 root root 0 Dec 28 00:42 _f_i_l_e_3_

'./sub dir 2':
total 0
-rw-r--r-- 1 root root 0 Dec 28 00:42 file_2_
-rw-r--r-- 1 root root 0 Dec 28 00:42 _f_i_l_e_4_

Some notes on each command:

1. creates two subdirectories, where the second has spaces in its name.

2. lists the contents recursively. note the single quotes are used on files or folders having spaces.

3. use find to find files (-type f) and echo the name to "FILES.txt" in the parent dir.

4. use while loop to iterate over each line in the file. IFS= clears the input field separator so leading and trailing whitespace isn't truncated.

   4.1 extracts the directory name, which shouldn't be modified

   4.2 gets the file name

   4.3 replaces one or more consecutive space chars with a single underscore in the file name

   4.4 verbosely renames the files, but not the folders.

5. lists the contents recursively. note the single quotes are used on files or folders having spaces.

I used parameter expansion for getting the dir names and file names instead of dirname and basename because it's faster.