NAME
Divert - Text Diversion Filter
SYNOPSIS
divert [-o outputfile] [-q] [-v] [inputfile]
DESCRIPTION
The divert program reads inputfile or from "stdin" and applies a 2-pass
diversion filter to its contents. In pass 1 all diversion locations are
accumulated and in pass 2 these locations are recursively expanded at
their dump positions. The diversion filter is controlled by directives
found in the input data:
{#NAME#} (or <<NAME>>)
This defines the dump position of the location NAME. All
accumulated data which finally has to been diverted to NAME is
inserted at this data position. Notice: the final data of a
location NAME has not to be known at this point, because the
expansion of such location dumps are done in pass 2. You can also
dump a location more than once, but the contents is always the
same, independent of the data position where the location dump tag
stays. The NAME can be any symbolic name matching
"[a-zA-Z][a-zA-Z0-9_]*".
{#[!]NAME[!]#: (or ..[!]NAME[!]>>)
This enters the location NAME (or diverts the data flow to it,
hence the name for this filter). In other words: the data flow now
goes on at location NAME. All following data (up to end of file or
the next location leave tag) gets appended to location NAME. You
can nest diversions by entering other locations at any point,
because the locations are remembered on a stack. The default
entered location is named ‘‘"main"’’. The top most location is
named ‘‘"null"’’ which neither can be entered nor leaved
explicitly. But of course the ‘‘"null"’’ diversion can be manually
dumped, for instance when using it for error messages.
There are two special features for diverting data which are
controlled by the ""!"" characters preceding or following the NAME
identifier:
!NAME
This sets the data flow position to the begin of location NAME,
i.e. it actually discards the current (already diverted)
contents of location NAME before entering it. Use this to
overwrite a locations contents.
NAME!
This marks this location entry as overwritable, i.e. it enters
location NAME but when the corresponding leave tag is found,
the data-flow position for NAME gets automatically reset to its
begin. Use this if you want to set the default contents for a
location which only gets used if no other diversions occur to
it (because any following diversions to this location will be
overwrite the contents). This feature is usually used for a
template scheme.
!NAME!
Just the combination of the above two features. Use this to
both discard the current contents of location NAME and set a
new default for it.
:#[NAME]#} (or <<[NAME]..)
This leaves the current location, i.e. enters again the location
which was active when this location was entered. There is no need
to leave all locations at the end of the input data. All still
entered locations are automatically left at end of file because
this is essential for a template scheme.
Notice that there are two ways of using (and thinking) about the
filtering mechanism this program provides:
Macro Mechanism
This is the "predefined" way of thinking here. Use it like this:
FOO
{#BAR#}
QUUX
{#BAR#:
BAZ
:##}
Here you are thinking of the mechanism as a macro mechanism where
you expand a macro at one data position while you define it via
begin and end tags.
Diversion Mechanism
This is the alternative way of thinking. Use it like this:
FOO
<<BAR>>
QUUX
..BAR>>
BAZ
<<..
In other words: You are thinking of the mechanism as a diversion
mechanism where you dump a location at one data position while you
divert to it by entering end leaving the location (here BAR) at
other positions.
You can even intermix both ways because both are just alternative
syntax variants which are treated the same.
EXAMPLE
{#HEAD#}
{#BODY#}
{#FOOT#}
{#FOOT#:
Quux
:##}
{#BODY#:
Bar
:##}
{#HEAD#:
Foo
:##}
OPTIONS
-o outputfile
This redirects the output to outputfile. Usually the output will be
send to stdout if no such option is specified or outputfile is
‘‘"-"’’.
-q This sets quiet mode where warnings are suppressed.
-v This sets verbose mode where some processing information will be
given on stderr.
AUTHORS
Ralf S. Engelschall
rse@engelschall.com
www.engelschall.com
Denis Barbier
barbier@engelschall.com