General Form of MOS Internal File Formats

Ideally all communication would be done via FITS tables. Unfortunately FITS tables are not possible to edit with many text editors, and not everyone has access to FTOOLS or the STSDAS tables package.

Instead we define ASCII text files with inspiration drawn from FITS tables. These are intended to be easy to create and edit. A rough specification of these files follows.

The first line of a file

The first line of a file must be a ``Magic Number'' in the sense used by the Unix file program. This is a specific character string which identifies the file format and version.

Blanks and comments

Blank lines will be ignored. Unless otherwise specified all lines whose first non-blank character is `#' (ASCII 043 = 0x23 = 35) will be ignored. Comments and blank lines for purposes of separation may thus be inserted anywhere in a file.

Keyword/Value pairs

Keywords will be case insensitive strings with no embedded blanks followed immediately by a colon. Values will be the remainder of the line following the colon.


Files are permitted to contain one table following the keyword/value pairs. The beginning of the table is marked by another line containing a magic number.

The design of these tables should consider the probable maximum line length of each entry. Whenever possible this should be kept within limits that are comfortable for text editors.

The order of the table columns must match that expected by the reading software. Column entries may not contain embedded whitespace. Quoted strings are not permitted. The final column in the table may be an exception; if interpreted as a string it may contain arbitrary strings with embedded whitespace.

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Steve Allen <>