#5 manipulate strings via shell commands

Hi

Let's say I have an SVG file and want to divide all
width attributes of all rect elements by two.

If the value of the selected attribute would be
automatically piped to the shell command then something
like the following could work:

xmlstar ed -u "//rect/@width" -r "ruby -e 'print
$stdin.read.to_f/2'"

"-r" for result, or "-s" for shell perhaps.

Tobi

[Mikhail Grushinskiy]

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Running another process for this is too much overhead.
It could have been done just with XPATH.

Currently 'ed' option doesn't allow expressions based on
current values in the document. But this is planned (see xml
ed -x option).

Here is how I think it will be possible in future

xml ed -u "//rect/@width" -x "@width/2"

Thanks for pointing this. I know that this is serious deficiency,
as there can bee need to modify somesthing in the document
based on what is already there (ex increment value).

--Mikhail

[Anonymous]

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user_id=769974

Hi Mikhail

> Running another process for this is too much overhead.

Not in all scenarios. XMLStarlet is quite fast and
lightweight (unlike
xsh or Java tools for example).

On Unix it is very common to call two, three, and more tools
in one
command line (chained pipes). Calling XMLStarlet with a
command that
involves calling tools like sed or tr still introduces very
little
overhead.

> It could have been done just with XPATH.

Yes, it's just a simple example meant as illustration.

> Currently 'ed' option doesn't allow expressions based on
> current values in the document. But this is planned (see xml
> ed -x option).

I know :)

> Here is how I think it will be possible in future
>
> xml ed -u "//rect/@width" -x "@width/2"

I'm looking forward to this feature, and I'll happily
feature it in
http://www.pinkjuice.com/howto/vimxml/ .

> Thanks for pointing this. I know that this is serious
> deficiency,
> as there can bee need to modify somesthing in the document
> based on what is already there (ex increment value).

Exactly.

For cases where XPath is sufficient the above feature (-x) is
sufficient, lightweight, fast, and useful.

For cases where XPath is not sufficient/appropriate [1] (eg
"change
all element names to be lowercase", "insert current date in
element
'last-change'", etc) it would be very useful if we could
call the
comandline.

I really think it would be the best strategy to offer both
features.
We need XPath for updated values since it knows XML. But
XPath is not
a string manipulation language so we also need to be able to
call
tools like sed and tr, and for heavier lifting even full
languages
such as Perl, Ruby. Only one simple feature is required
(pipe the
string to the shell command), and we have all the power of
commandline tools available.

Tobi

[1]
complex string manipulation in XPath would involve extremely
long
commandlines