how to fix a unix shell script to work on linux

[Kurt Granroth]

Josef Lowder wrote:
> The following script used to work on my old unix system, 
> to remove blank lines from a text file.  It no longer works 
> on linux, but now it gives an error message (below): 
> 
> sed '/[!-~]/!d' $1
> 
> 
> This is the error message:
> 
> sed: -e expression #1, char 7: Invalid range end
> 
> How can I fix this?

Hmm... this is a puzzle.  First, as others have noted, this snippet
doesn't just delete blank lines... it deletes any line that doesn't
contain at least one 'graph' character (all printable chars except a space).

Given that as a constraint, this new-fangled sed syntax does exactly
what you have above:

sed '/[[:graph:]]/!d' $1

But let's examine what you do have.  When I run this exact command using
GNU sed 4.1.5, *all* lines are deleted, not just blank ones.  I then
played around with it a bit and substituted chars for the ! going up ("
then # then $, etc).  All deleted all lines until I got to this:

sed '/0-~/!d'
sed: -e expression #1, char 7: Invalid range end

Interesting!  Likewise, working backwards from the ~, I get the exact
same error message until I have this:

sed '/0-z/!d'

That finally works.  What gives, though?  That implies that non
alphanumeric chars cannot be used in a range... which is just wrong
since, for instance, [[:graph:]] is a direct substitute for [!-~].  Or
maybe it really is just those final chars:

sed '/[!-z]/!d'

That worked just fine.  So it's {, |, }, and ~ that are messing with the
range.

I then tried this:

sed '/!-\x7a/!d'

That worked just like !-z as I would expect.  I then replace the tilde
with 7e (its hex):

sed '/!-\x7e/!d'

Nothing... it deletes every line.  Replacing ! with 0:

sed '/0-\x7e/!d'
sed: -e expression #1, char 10: Invalid range end

That really smacks of a GNU sed bug to me.  I just tend to think that
something like this would have been discovered a long time ago and so
perhaps we're just using it incorrectly.

Any sed expert want to comment?

Kurt

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