Git: Squash old commits (rebase -i)

$ git rebase -i HEAD^x

# Rebase X..Y onto X (1 command)

Commands:
p, pick <commit> = use commit
r, reword <commit> = use commit, but edit the commit message
e, edit <commit> = use commit, but stop for amending
s, squash <commit> = use commit, but meld into previous commit
f, fixup <commit> = like "squash", but discard this commits log message
x, exec <command> = run command (the rest of the line) using shell
b, break = stop here (continue rebase later with 'git rebase --continue')
d, drop <commit> = remove commit
l, label <label> = label current HEAD with a name
t, reset <label> = reset HEAD to a label
m, merge [-C <commit> | -c <commit>] <label> [# <oneline>]
.       create a merge commit using the original merge commits
.       message (or the oneline, if no original merge commit was
.       specified). Use -c <commit> to reword the commit message.

These lines can be re-ordered; they are executed from top to bottom.