On 8/28/15 7:28 PM, Helmut Karlowski wrote:
> Hello
>
> The bash-manual says:
>
> Words of the form $'string' are treated specially. The word expands to
> string, with backslash-escaped characters replaced as specified by the
> ANSI C standard. Backslash escape sequences, if present, are decoded as
> follows:
>
> ...
>
> \cx a control-x character
>
> Now when I run this:
>
> {
> echo $LINENO $'\h\ca\ek'
> echo $LINENO $'\h\cA\ek'
> echo $LINENO $'\h\cd\ek'
> echo $LINENO $'\h\c\d\ek'
> echo $LINENO $'\h\c|d\ek'
> echo $LINENO $'\h\c<d\ek'
> echo $LINENO $'\h\c d\ek'
> echo $LINENO $'\h\\c d\ek'
> } | tee /dev/stderr | od -ax
>
> I get (output pasted from my editor):
>
> 2 \h^A^[k
> 3 \h^A^[k
> 4 \h^D^[k
> 5 \h^\d^[k
> 6 \h^\d^[k
> 7 \h^\d^[k
> 8 \h
> 9 \h\c d^[k
> 0000000 2 sp \ h soh esc k nl 3 sp \ h soh esc k nl
> 2032 685c 1b01 0a6b 2033 685c 1b01 0a6b
> 0000020 4 sp \ h eot esc k nl 5 sp \ h fs d esc k
> 2034 685c 1b04 0a6b 2035 685c 641c 6b1b
> 0000040 nl 6 sp \ h fs d esc k nl 7 sp \ h fs d
> 360a 5c20 1c68 1b64 0a6b 2037 685c 641c
> 0000060 esc k nl 8 sp \ h nl 9 sp \ h \ c sp d
> 6b1b 380a 5c20 0a68 2039 685c 635c 6420
> 0000100 esc k nl
> 6b1b 000a
> 0000103
>
> I wonder about the lines 6, 7, 8: 6,7: all non-alnum-characters (here | and
> <) are printed as 0x1c?
Conversion to a control character is effected by ANDing with 0x1f, since
the valid control character range is 0-0x1f. If you have something that's
not a valid control character after being ANDed with 0x1f, you get
undefined results.
There is a table in
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/stty.html#tag_20_123
that has the list of valid characters.
> And line 8: Why is the output truncated after '\c '?
Space is outside the range of a control character, and, as it happens,
<space>&0x1f == 0. The NUL causes the string to be truncated.
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU c...@case.edu http://cnswww.cns.cwru.edu/~chet/
