swapping characters in ex

Question

I am pretty new to vim and ex and I was wondering if anyone could help me with an area I am fuzzy on. I would like to know how to swap characters on every line or occurrence of a pattern. For example How would I swap the first 2 characters of every line in a file. I know it can be done and I'm pretty sure it involves the use of parentheses to store the chars. But thats is all I know. Also, Say I wanted to replace the 2nd char on everyline with some string, how would I do that?

Answer 1

To replace second character in each line to r in vim: :%s/^\(.\)./\1r/:

• :%s/p/r/ replace pattern p with r for all lines (because of %);
• ^ start line;
• \( start a group;
• . any character (the first in this example);
• \) end the group;
• . any character (the second in this example);
• \1 back reference to the first group (the first character in this example);
• r replacement text.

To swap two first characters: :%s/^\(.\)\(.\)/\2\1/.

Answer 2

Swapping the first two characters on every line:

:%s/^\(.\)\(.\)/\2\1/g

Replacing the second character on every line with "string":

:%s/^\(.\)\(.\)/\1string/g

More info on the substitute command: http://vim.wikia.com/wiki/Search_and_replace

Answer 3

You can do the following to swap the two first chars of every line in the buffer:

:%norm xp

or:

:%s/\v^(.)(.)/\2\1

You'll need the :global command to apply the commands above on every line matching a specific pattern:

:g/foo/norm xp

or:

:g/foo/s/\v^(.)(.)/\2\1

Reference:

:help :normal
:help :global
:help :s
:help range