A general sed question
olli at lurza.secnetix.de
Wed Oct 7 10:26:52 UTC 2009
David Allen <the.real.david.allen at gmail.com> wrote:
> I keep bumping up against this, so I thought I'd throw this question out
> to those who understand sed better than I do.
> What I'm trying to do is to clean up the contents of some files
> (/sys/i386/conf/GENERIC would be a good example) to get more readable
> diffs. To that end, I'm trying to use sed to
> - delete commented lines
> - remove inline comments
> - remove trailing spaces and/or tabs
> - delete blank lines, and/or lines containing just spaces and/or tabs
> - expand tabs
I recommend to use the -Bb options of diff. They cause diff
to ignore blank lines and any changes in the amount of white
space (including tabs). You can also use -w to ignore *all*
white space, but note that "foo bar" and "foobar" are then
considered equal, which might not be what you want.
So only the removal of comments remains:
That will remove all comments. Afterwards, commented lines
are empty, so the -B option of diff will ignore them, so you
don't have to remove them explicitly.
When using zsh as your shell, you can use a nice feature
called "process substitution", so you don't have to create
diff -Buw <(sed 's/#.*//' GENERIC) <(sed 's/#.*//' MYKERNEL)
I think bash has a similar feature, but I don't know the
syntax, so please see the manpage if you're a bash user.
If you need to do that oftem, it's worth to create an alias
or shell function.
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