Archive of old man pages? specifically for the features available for grep in early ‘ed’

Man pages, once changed to a human-readable form, are text files that you can diff with whatever tool that suits you. Here are two examples, as two bash functions, for two tools: diff and vimdiff. Adapt them to your favorite tool.

With vimdiff:

vimdiff_man() { vimdiff -R <(man --manpath="/old/path/to/man" "$1") <(man "$1"); }

With diff, side by side, adjusted to your screen width:

diff_man() (
    width="${COLUMNS:-80}"
    export MANWIDTH=$((width / 2 - 2))
    diff -y -W"$width" <(man --manpath="/old/path/to/man" "$1") <(man "$1") | less
)

In each function, I'm diffing between two pseudo files <(...), each of which containing the result of the man command between parentheses (this is bash's Process Substitution).

/old/path/to/man is the directory hierarchy containing your old manual pages. It is expected to have the same secondary man levels man1, man2, ... as your main manual directory (probably /usr/share/man). Change it to fit your needs.

Usage:

diff_man sshd_config
vimdiff_man sshd_config

grep is only meant to (and was only initially) print(ing) the lines matching a pattern. That's what grep means (based on the g/re/p ed command).

Now, some grep implementations have added a few features that encroaches a bit on the role of other commands. For instance, some have some -r/--include/--exclude to perform part of find's job.

GNU grep added a -o option that makes it perform parts of sed's job as it makes it edit the lines being matched.

pcregrep extended it with -o1, -o2... to print what was matched by capture groups. So with that implementation, even though it was not designed for that, you can actually replace:

sed 's/old/new/'

with:

pcregrep --om-separator=new  -o1 -o2 '(.*?)old(.*)'

That doesn't work properly however if the capture groups match the empty string. On an input like:

XoldY
Xold
oldY

it gives:

XnewY
X
Y

You could work around that using even nastier tricks like:

PCREGREP_COLOR= pcregrep --color=always '.*old.*' |
  pcregrep --om-separator=new -o1 -o2 '^..(.+?)old(.+)..' |
  pcregrep -o1 '.(.*).'

That is, prepend and append \e[m (coloring escape sequence) to all matching lines to be sure there is at least one character on either side of old, and strip them afterwards.