A general sed question
freebsd at optimis.net
Thu Oct 8 00:56:38 UTC 2009
On Tue, Oct 06, 2009 at 11:45:36PM -0700, David Allen 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
For the following note that what's contained in the square brackets is a
space character followed by a literal TAB character (typically created
by entering ^V followed by TAB).
> - delete commented lines
> - remove inline comments
s/[ ]*#.*// # takes care of both, but will leave \t\t\t\n
> - remove trailing spaces and/or tabs
s/[ ]*$// # handy, but not needed if using diff -b
> - delete blank lines, and/or lines containing just spaces and/or tabs
> - expand tabs
This is overly complex with sed and probably unecessary. Instead I'd
suggest using your editor (in vim, it's ':set expandtab | retab'), or
for interactive use, relying on expand(1) and using a value for -t that
matches the tab spacing you typically use for your pager and/or editor.
Alternatively, to get better visual alignment when using diff(1), just
use the -t option.
Putting the above together, you get
sed -e 's/[ ]*#.*//' -e 's/[ ]*$//' -e '/^[ ]*$/d'
Hardly ideal but it's readable enough and satisfies the 80/20 rule. If
used as a simple alias, shell function or script as Oliver Fromme
suggested (yes, this works in bash), my suggestion is
diff -ubBt <(cleanup /sys/i386/conf/GENERIC) <(cleanup /path/to/NEWKERNEL)
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