[Discuss] "M-" notation

[feenberg at nber.org (Daniel Feenberg)]

On Thu, 5 Jul 2012, Richard Pieri wrote:

> On 7/5/2012 8:00 PM, Daniel Feenberg wrote:
>> "cat -v" has acquired something new called "M-" notation. It is
>> mentioned but not described in the man page for cat,
>
>       -v, --show-nonprinting
>              use ^ and M- notation, except for LFD and TAB
>
> "--show-nonprinting" seems self-explanatory.
>
>> but apparently tr doesn't support it.
>
> Because the option is for humans to read, not for programs to parse.  In
> other words, it's "make all the nonprinting characters printing for my
> benefit just this once."
>
>> Any suggestions on how to delete all the "M- " characters from a
>> file?
>
> You don't, because that includes tabs and end-of-line characters.  If

Actually, tab and NL are not translated. From the man page:

    -v, --show-nonprinting
               use ^ and M- notation, except for LFD and TAB

I just tested it, the man page is almost right in that CR is also not 
translated. Anyway, I don't want to delete all the "M-" characters, just 
"M- " (em minus space). That character acts like a tab on my terminal, but 
seems to be a tab with the high bit set.

> you want to remove specific characters then do so with sed or 'tr -d'
> and with the appropriate interpreted sequences or octal codes.  If you try to 
> do it with 'tr -d [:cntrl:]' then you'll end up with a mess.
>
> -- 
> Rich P.
>
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