In Gnuastro, arguments are almost exclusively used as the input data file names. Please consult the first few paragraph of the “Invoking ProgramName” section for each program for a description of what it expects as input, how many arguments, or input data, it accepts, or in what order. Everything particular about how a program treats arguments, is explained under the “Invoking ProgramName” section for that program.
Generally, if there is a standard file name extension for a particular format, that filename extension is used to separate the kinds of arguments. The list below shows the data formats that are recognized in Gnuastro’s programs based on their file name endings. Any argument that doesn’t end with the specified extensions below is considered to be a text file (usually catalogs, see Tables). In some cases, a program can accept specific formats, for example ConvertType also accepts .jpg images.
Through out this book and in the command-line outputs, whenever we want to generalize all such astronomical data formats in a text place holder, we will use ASTRdata, we will assume that the extension is also part of this name. Any file ending with these names is directly passed on to CFITSIO to read. Therefore you don’t necessarily have to have these files on your computer, they can also be located on an FTP or HTTP server too, see the CFITSIO manual for more information.
CFITSIO has its own error reporting techniques, if your input file(s) cannot be opened, or read, those errors will be printed prior to the final error by Gnuastro.