6.3 Specifying a List of Columns

If an argument is specified in the help text for a command with the symbol <colid-list> it means you must give a string which identifies a list of zero, one or more of the existing columns in a table. The string you specify is a separated into separate tokens by whitespace, which means that you will normally have to surround it in single or double quotes to ensure that it is treated as a single argument and not several of them.

Each token in the <colid-list> string may be one of the following:

Column Name

The name of a column may be used if it contains no spaces and doesn't start with a minus character ('-'). It is usually matched case insensitively. If multiple columns have the same name, the first one that matches is selected.

Column Index or $ID

The index of the column may always be used; this is a useful fallback if the column name isn't suitable for some reason. The first column is '1', the second is '2' and so on. You may alternatively use the forms '$1', '$2' etc.

Tip: if counting which column has which index is giving you a headache, running tpipe with omode=meta or omode=stats on the table may help.

Wildcard Expression

You can use a simple form of wildcard expression which expands to any columns in the table whose names match the pattern. Currently, the only special character is an asterisk '*' which matches any sequence of characters. To match an unknown sequence at the start or end of the string an asterisk must be given explicitly. Other than that, matching is usually case insensitive. The order of the expanded list is the same as the order in which the columns appear in the table.

Thus "col*" will match columns named col1, Column2 and COL_1024, but not decOld. "*MAG*" will match columns named magnitude, ABS_MAG_U and JMAG. "*" on its own expands to a list of all the columns of the table in order.

Specifying a list which contains a given column more than once is not usually an error, but what effect it has depends on the function you are executing.