You wrote:
[...sort -M doesn't work the way I expect it to...]
Thanks for the report, but that's not due to a bug.
Two things might be causing trouble here:
- a common misunderstanding about how sort works with byte offsets:
without `-b' or the b attribute, each field includes leading delimiters
- a subtlety in the rules for determining whether global attributes affect
key specs
Use this in examples below
$ cat in
x Jun
a Jan
b Dec
You reported that this doesn't work:
$ sort -k2.1,2.3M in
a Jan
b Dec
x Jun
Now that you know about -b,
(aka --ignore-leading-blanks, if you're using textutils-2.0.14 or newer)
you might try this:
$ sort -b -k2.1,2.3M in
a Jan
b Dec
x Jun
but as you can see above, that doesn't work either.
The following, with a local `b' attribute appended, doesn't work either:
$ sort -k2.1,2.3Mb in
a Jan
b Dec
x Jun
But the following *does* work, with the `b' attribute applied to
the starting position:
$ sort -k2.1b,2.3M in
a Jan
x Jun
b Dec
Applying `b' to the starting position makes sort remove *leading* delimiters.
The second example highlights a subtlety in how global attributes (from
options like -b) are `inherited' (or not) by individual `key specs'.
A global attribute is inherited by a key spec IFF that key spec has no
local modifiers. In the example above, there is a local `M' modifier,
so the global -b had no effect on that key spec. Another way to make
this simple example work properly is to use only global attributes:
$ sort -bM -k 2.1b,2.3 in
a Jan
b Dec
x Jun
Note that on some older systems, your example would have worked
just fine. E.g. Solaris5.5.1's /bin/sort -M strips leading blanks,
while Solaris 8's /bin/sort -M does not.
Here's a note from the documentation `info sort':
Historical (BSD and System V) implementations of `sort' have
differed in their interpretation of some options, particularly `-b',
`-f', and `-n'. GNU sort follows the POSIX behavior, which is usually
(but not always!) like the System V behavior. According to POSIX, `-n'
no longer implies `-b'. For consistency, `-M' has been changed in the
same way. This may affect the meaning of character positions in field
specifications in obscure cases. The only fix is to add an explicit
`-b'.
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