This required parameter can be one or more of the following:

Blocks - Summarize all the blocks (images or tables) in the file, one line per block.

Keys - List the CXC Data Model (ASCDM) header keys for the selected block. Remember that not all the FITS keywords in a FITS file will be included - the ones like EXTNAME and CRPIX that have a special meaning for the structure of the file don't count as CXC Data Model keys, their values show up in other places (e.g. the output from cols). With this option, the comment and history records are suppressed. To see the low level list of all raw FITS header keywords in a FITS file, use opt=header,raw.

Comments - List the ASCDM comment keys for the block. For a FITS file, these keys are the COMMENT and HISTORY keywords.

Cols - List the ASCDM columns for the selected block. Shows `vector columns' like (X,Y) as pairs. This output shows the names of the variables you can filter a table on and what their valid ranges are. If the block is an image, it gives you one column with the name of the image (images are interpreted as a table with a single row and column).

Subspace - Summarizes the data subspace for the block. This describes the filters that have been applied to the data, either by the user or in processing.

Data - Prints the data segment. The cells parameter controls how much of an array column gets printed. By default, the data is printed in an `ornate' format showing arrays grouped in parentheses etc. If you use "Clean" option as well, the output is in a simpler format suitable for reading by other analysis programs. The output format for image data is currenlty not well supported.

Counts - Returns the number of events in the file. If a filter is applied (row numbers, sky region, etc.), the counts in the filtered region are printed to the screen. If a non-event file is given (e.g. PI spectrum or RMF file), the number of rows in the file is returned.

Header - Equivalent to Keys,Comments. List both DM level header keys and comment/history records. - List the ASCDM header keys for the selected block. Remember that not all the FITS keywords in a FITS file will be included - the ones like EXTNAME and CRPIX that have a special meaning for the structure of the file don't count as ASCDM keys, their values show up in other places (e.g. the output from cols). To see the low level list of raw FITS header keywords in a FITS file, use opt=header,raw.

Struct - Equivalent to 'header,cols,subspace'

Full - Equivalent to 'blocks,header,cols,subspace,data'

Array - Prints the data segment, but with arrays printed vertically. The cells parameter controls how much of an array column gets printed.

All - Print the info selected by the other options for all the blocks in the dataset.

Clean - When used in conjunction with the Array or Data options, produces stripped down output suitable for parsing by other programs.

Raw - Provides a lower level view of the header. 'header,raw' lists the raw FITS header keywords, not just the data model keywords. The old 'data,raw' functionality is now provided by 'data,clean'.

The output ASCII file to be created; output is sent to the screen if this parameter is blank.

rows=30:40 Print row 30 to row 40 rows=40 Print row 1 to 40 rows=40:40 Print only row 40 rows=" " Print all rows (this is the DEFAULT) rows=-1 Print all rows

This parameter allows to select a range of array indices to print in array columns and in images. Examples: cells = 1:8 Print only array elements 1 to 8 of each array cells = all Print all array elements.

The verbose parameter provides debugging information; verbose = 0 is usually fine.