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### B.26.1 Usage

The usage of `tcat` is

       stilts <stilts-flags> tcat in=<table> [<table> ...] ifmt=<in-format>
                                  multi=true|false istream=true|false icmd=<cmds>
                                  ocmd=<cmds>
                                  omode=out|meta|stats|count|checksum|cgi|discard|topcat|samp|plastic|tosql|gui
                                  out=<out-table> ofmt=<out-format>
                                  seqcol=<colname> loccol=<colname>
                                  uloccol=<colname> lazy=true|false
                                  countrows=true|false

If you don't have the `stilts` script installed, write "`java -jar stilts.jar`" instead of "`stilts`" - see Section 3. The available `<stilts-flags>` are listed in Section 2.1. For programmatic invocation, the Task class for this command is `uk.ac.starlink.ttools.task.TableCat`.

Parameter values are assigned on the command line as explained in Section 2.3. They are as follows:

`countrows = true|false` (Boolean)
  Whether to count the rows in the table before starting the output. This is essentially a tuning parameter - if writing to an output format which requires the number of rows up front (such as normal FITS) it may result in skipping the number of passes through the input files required for processing. Unless you have a good understanding of the internals of the software, your best bet for working out whether to set this true or false is to try it both ways

  [Default: `false`]

`icmd = <cmds>` (ProcessingStep[])
  Specifies processing to be performed on each input table as specified by parameter `in`, before any other processing has taken place. The value of this parameter is one or more of the filter commands described in Section 6.1. If more than one is given, they must be separated by semicolon characters (";"). This parameter can be repeated multiple times on the same command line to build up a list of processing steps. The sequence of commands given in this way defines the processing pipeline which is performed on the table.

  Commands may alteratively be supplied in an external file, by using the indirection character '@'. Thus a value of "`@filename`" causes the file `filename` to be read for a list of filter commands to execute. The commands in the file may be separated by newline characters and/or semicolons, and lines which are blank or which start with a '`#`' character are ignored.

`ifmt = <in-format>` (String)
  Specifies the format of the input table as specified by parameter `in`. The known formats are listed in Section 5.1.1. This flag can be used if you know what format your table is in. If it has the special value `(auto)` (the default), then an attempt will be made to detect the format of the table automatically. This cannot always be done correctly however, in which case the program will exit with an error explaining which formats were attempted. This parameter is ignored for scheme-specified tables.

  The same format parameter applies to all the tables specified by `in`.

  [Default: `(auto)`]

`in = <table> [<table> ...]` (TableProducer[])
  Locations of the input tables. Either specify the parameter multiple times, or supply the input tables as a space-separated list within a single use.

  The following table location forms are allowed:

  - A filename.
  - A URL.
  - The special value "`-`", meaning standard input. In this case the input format must be given explicitly using the `ifmt` parameter. Note that not all formats can be streamed in this way.
  - A scheme specification of the form `:<scheme-name>:<scheme-args>`.
  - A system command line with either a "`<`" character at the start, or a "`|`" character at the end ("`<syscmd`" or "`syscmd|`"). This executes the given pipeline and reads from its standard output. This will probably only work on unix-like systems.
  Compression in any of the supported compression formats (Unix compress, gzip or bzip2) is expanded automatically.

  A list of input table locations may be given in an external file by using the indirction character '@'. Thus "`in=@filename`" causes the file `filename` to be read for a list of input table locations. The locations in the file should each be on a separate line.

`istream = true|false` (Boolean)
  If set true, the input table specified by the `in` parameter will be read as a stream. It is necessary to give the `ifmt` parameter in this case. Depending on the required operations and processing mode, this may cause the read to fail (sometimes it is necessary to read the table more than once). It is not normally necessary to set this flag; in most cases the data will be streamed automatically if that is the best thing to do. However it can sometimes result in less resource usage when processing large files in certain formats (such as VOTable). This parameter is ignored for scheme-specified tables.

  The same streaming flag applies to all the tables specified by `in`.

  [Default: `false`]

`lazy = true|false` (Boolean)
  Whether to perform table resolution lazily. If true, each table is only accessed when the time comes to add its rows to the output; if false, then all the tables are accessed up front. This is mostly a tuning parameter, and on the whole it doesn't matter much how it is set, but for joining an enormous number of tables setting it true may avoid running out of resources.

  [Default: `false`]

`loccol = <colname>` (String)
  Name of a column to be added to the output table which will contain the location (as specified in the input parameter(s)) of the input table from which each row originated.
`multi = true|false` (Boolean)
  Determines whether all tables, or just the first one, from input table files will be used. If set `false`, then just the first table from each file named by `in` will be used. If `true`, then all tables present in those input files will be used. This only has an effect for file formats which are capable of containing more than one table, which effectively means FITS and VOTable and their variants.

  [Default: `false`]

`ocmd = <cmds>` (ProcessingStep[])
  Specifies processing to be performed on the output table, after all other processing has taken place. The value of this parameter is one or more of the filter commands described in Section 6.1. If more than one is given, they must be separated by semicolon characters (";"). This parameter can be repeated multiple times on the same command line to build up a list of processing steps. The sequence of commands given in this way defines the processing pipeline which is performed on the table.

  Commands may alteratively be supplied in an external file, by using the indirection character '@'. Thus a value of "`@filename`" causes the file `filename` to be read for a list of filter commands to execute. The commands in the file may be separated by newline characters and/or semicolons, and lines which are blank or which start with a '`#`' character are ignored.

`ofmt = <out-format>` (String)
  Specifies the format in which the output table will be written (one of the ones in Section 5.1.2 - matching is case-insensitive and you can use just the first few letters). If it has the special value "`(auto)`" (the default), then the output filename will be examined to try to guess what sort of file is required usually by looking at the extension. If it's not obvious from the filename what output format is intended, an error will result.

  This parameter must only be given if `omode` has its default value of "`out`".

  [Default: `(auto)`]

`omode = out|meta|stats|count|checksum|cgi|discard|topcat|samp|plastic|tosql|gui` (ProcessingMode)
  The mode in which the result table will be output. The default mode is `out`, which means that the result will be written as a new table to disk or elsewhere, as determined by the `out` and `ofmt` parameters. However, there are other possibilities, which correspond to uses to which a table can be put other than outputting it, such as displaying metadata, calculating statistics, or populating a table in an SQL database. For some values of this parameter, additional parameters (`<mode-args>`) are required to determine the exact behaviour.

  Possible values are

  - `out`
  - `meta`
  - `stats`
  - `count`
  - `checksum`
  - `cgi`
  - `discard`
  - `topcat`
  - `samp`
  - `plastic`
  - `tosql`
  - `gui`
  Use the `help=omode` flag or see Section 6.4 for more information.

  [Default: `out`]

`out = <out-table>` (TableConsumer)
  The location of the output table. This is usually a filename to write to. If it is equal to the special value "-" (the default) the output table will be written to standard output.

  This parameter must only be given if `omode` has its default value of "`out`".

  [Default: `-`]

`seqcol = <colname>` (String)
  Name of a column to be added to the output table which will contain the sequence number of the input table from which each row originated. This column will contain 1 for the rows from the first concatenated table, 2 for the second, and so on.
`uloccol = <colname>` (String)
  Name of a column to be added to the output table which will contain the unique part of the location (as specified in the input parameter(s)) of the input table from which each row originated. If not null, parameters will also be added to the output table giving the pre- and post-fix string common to all the locations. For example, if the input tables are "/data/cat_a1.fits" and "/data/cat_b2.fits" then the output table will contain a new column <colname> which takes the value "a1" for rows from the first table and "b2" for rows from the second, and new parameters "<colname>_prefix" and "<colname>_postfix" with the values "/data/cat_" and ".fits" respectively.

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STILTS - Starlink Tables Infrastructure Library Tool Set
Starlink User Note256
STILTS web page: http://www.starlink.ac.uk/stilts/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk