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A.2.1 Usage

Using tpipe is more like using a Unix pipeline than using a single Unix command. You give an input specifer which determines the table to be operated on, some filter specifiers which determine the operations which will be performed on it, and an output specifier which determines what should happen to the processed data. The table is streamed through the processing filters in the order in which you've given them, and the processed data are eventually sent to the destination, which may be an output table file or some other operation like displaying it in TOPCAT or calculating the per-column statistics. In most cases the processing is passed through the pipeline a row at a time, meaning that the amount of memory required is small (though in some cases, for instance sorting, this is not possible). Although a similar effect could be achieved by stringing together several single-operation tpipe invocations in an actual Unix pipe, with the data flowing between the commands in byte streams using one or other of the supported table formats, the way tpipe works makes it much more efficient to do all the work within one invocation.

The basic form of a tpipe invocation is therefore

    tpipe <input-specifier> <filter-specifiers> <mode-specifier> <other-flags>
(though in fact these elements can appear in any order and they are all optional). If you don't have the Unix scripts installed, invoke it as described in Section 2 using the classname uk.ac.starlink.ttools.TablePipe.

The different sets of arguments are described in the following subsections. There are many different flags, some with supplementary arguments, which may look daunting. However, if you make an error in specifying them, tpipe will try to print a message which explains what has gone wrong, so with a little bit of trial and error it should be possible to make it do what you want.


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STILTS - Starlink Tables Infrastructure Library Tool Set
Starlink User Note 256
STILTS web page: http://www.starlink.ac.uk/stilts/
Author email: m.b.taylor@bristol.ac.uk