Regular expression - replace all spaces in beginning of line with periods

Question

I don't care if I achieve this through vim, sed, awk, python etc. I tried in all, could not get it done.

For an input like this:

top           f1    f2    f3
   sub1       f1    f2    f3
   sub2       f1    f2    f3
      sub21   f1    f2    f3
   sub3       f1    f2    f3

I want:

top           f1    f2    f3
...sub1       f1    f2    f3
...sub2       f1    f2    f3
......sub21   f1    f2    f3
...sub3       f1    f2    f3

Then I want to just load this up in Excel (delimited by whitespace) and still be able to look at the hierarchy-ness of the first column!

I tried many things, but end up losing the hierarchy information

Answer 1

With this as the input:

$ cat file
top           f1    f2    f3
   sub1       f1    f2    f3
   sub2       f1    f2    f3
      sub21   f1    f2    f3
   sub3       f1    f2    f3

Try:

$ sed -E ':a; s/^( *) ([^ ])/\1.\2/; ta' file
top           f1    f2    f3
...sub1       f1    f2    f3
...sub2       f1    f2    f3
......sub21   f1    f2    f3
...sub3       f1    f2    f3

How it works:

• :a

  This creates a label a.

• s/^( *) ([^ ])/\1.\2/

  If the line begins with spaces, this replaces the last space in the leading spaces with a period.

  In more detail, ^( *) matches all leading blanks except the last and stores them in group 1. The regex ([^ ]) (which, despite what stackoverflow makes it look like, consists of a blank followed by ([^ ])) matches a blank followed by a nonblank and stores the nonblank in group 2.

  \1.\2 replaces the matched text with group 1, followed by a period, followed by group 2.

• ta

  If the substituted command resulted in a substitution, then branch back to label a and try over again.

Compatibility:

1. The above was tested on modern GNU sed. For BSD/OSX sed, one might or might not need to use:

   sed -E -e :a -e 's/^( *) ([^ ])/\1.\2/' -e ta file
   

   On ancient GNU sed, one needs to use -r in place of -E:

   sed -r ':a; s/^( *) ([^ ])/\1.\2/; ta' file
   

2. The above assumed that the spaces were blanks. If they are tabs, then you will have to decide what your tabstop is and make substitutions accordingly.

Answer 2

There are two different ways to do this in vim.

1. With a regex:

   :%s/^\s\+/\=repeat('.', len(submatch(0)))
   

   This is fairly straightforward, but a little verbose. It uses the eval register (\=) to generate a string of '.'s the same length as the number of spaces at the beginning of each line.

2. With a norm command:

   :%norm ^hviwr.
   

   This is a much more conveniently short command, although it's a little harder to understand. It visually selects the spaces at the beginning of a line, and replaces the whole selection with dots. If there is no leading space, the command will fail on ^h because the cursor attempts to move out of bounds.

   To see how this works, try typing ^hviwr. on a line that has leading spaces to see it happen.