bash - replace space with new line

Assuming you have a string with spaces as separators:

newline_separated=${space_separated// /$'\n'}

However you're probably asking the wrong question. (Not necessarily, for example this might come up in a makefile.) A space-separated list of file names doesn't really work: what if one of the file names contained spaces?

If a program receives file names as arguments, don't join them with spaces. Use "$@" to access them one by one. Although echo "$@" prints the arguments with spaces in between, that's due to echo: it prints its arguments with spaces as separators. somecommand "$@" passes the file names as separate arguments to the command. If you want to print the arguments on separate lines, you can use

printf '%s\n' "$@"

If you do have space-separated file names and you want to put them in an array to work on them:

split_list () {
  local IFS=' ' flags='+f'
  if [[ $- = *f* ]]; then flags=; fi
  set -f
  eval "$1=($2)"
  set $flags
}
split_list array '/path/to/file1 /path/to/file2 /path/to/file3'
for x in "${array[@]}"; do …

Be pragmatic, use sed!!

sed 's/\s+/\n/g' file

This is more or less:

'substitute /one space or more/ for /newline/ globally'

In this case I would use printf:

printf '%s\n' /path/to/file /path/to/file2 /path/to/file3 /path/to/file4 /path/to/file5

If there are spaces within the one of the paths, you can quote that filepath in order to prevent it from being split on the spaces:

printf '%s\n' /path/to/file '/path/to/file with spaces' /path/to/another/file

To transform text in general, tr is your best bet, as covered in an existing answer.

Another approach, assuming the line is in a variable called line:

for path in $line;do echo $path;done

This makes use of the fact that Bash splits its arguments on whitespace by default and that echo appends a newline to its input by default.

Here is how I did it:

echo "/path/to/file /path/to/file2 /path/to/file3 /path/to/file4 /path/to/file5" | sed 's/ /\
'/g

Notice the use of Enter key after backslash in the sed command.