Replace each leading tab by four spaces, recursively for every file

Question

What is the easiest way of achieving this using common tools in Linux?

I have looked at:

1. sed, but don't know enough about how to count the matched leading tabs in an expression like sed -i 's/^[\t]*/<what-to-put-here?>/g myFile.c.
2. astyle, but can't figure out how to tell it to just reindent and NOT format
3. indent, same problem as astyle
4. expand, but it also replaces non-leading tabs and I have to handle the inplace replacement myself which is error prone.

I was just looking for a quick and easy solution that I can plug into a find -type f -name "*.c" -exec '<tabs-to-spaces-cmd> {}' \;

Answer 1

You should really use expand since it is developed only to do that. From its documentation:

-i, --initial
   do not convert tabs after non blanks

So the command for a single file would be:

expand -i -t 4 input > output

In order to use it with multiple file you will need a trick:

expand_f () {
  expand -i -t 4 "$1" > "$1.tmp"
  mv "$1.tmp" "$1"
}

export -f expand_f
find -type f -iname '*.c' -exec bash -c 'expand_f {}' \;

This is used to prevent expand to write on the file while it is still processing it, and to avoid redirecting the stdout of find instead of the one of expand.

Answer 2

This might work for you (GNU sed):

sed -ri ':a;s/^( *)\t/\1    /;ta' file