IRAF and the CL

Working with Files

This section describes:

File structures commonly used in STSDAS and IRAF.
How to use directory specifications.
How to specify file names.

File Structures

Images used by IRAF and STSDAS consist of two files. The two files are always used together as a pair and will always have a file name that differs only in the last character of the extension:

A header file, which consists of descriptive information; these are ASCII text files for STSDAS images and a combination of ASCII text and binary for IRAF images. IRAF header files are identified by an extension of .imh. STSDAS header files are identified by an extension of .hhh or another extension ending in "h", such as .c0h or .q1h.
A binary data file,*1 consisting of pixel information. IRAF data file names end with a .pix extension. STSDAS data files end with an extension of .hhd or another extension that ends with "d", such as .c0d or .q0d.

STSDAS always expects both component files of a Generic Edited Information Set (GEIS) image to be kept together in the same directory. Both components must have the same root name.

When working with IRAF or STSDAS images, you need only specify the header file name--the tasks will automatically use the binary data file when necessary.

IRAF and STSDAS image formats are not similar in any way, other than that they each have two component files. The IRAF header is binary and has no fixed format, whereas the STSDAS format specifies 80 byte records consisting of ASCII text. The IRAF binary file consists of a grid of binary data preceded by a 512-byte binary description. The STSDAS binary file consists of a series of groups of binary data, each representing an entire image, and blocks of group description information called the Group Parameter Block (GPB).

See Chapter 3 on page 37 for more information about data formats.

Directory Specification

As we mentioned above, the two components of an STSDAS image are expected to be in the same directory, and tasks will look for these files in whatever directory you are currently located.*2

To navigate through directories, you should use the following commands:

path - Lists the current working directory.
cd directory - Move to the named directory.
show imdir - Lists the directory where IRAF pixel files will be stored.

Specifying Files

Most tasks in IRAF and STSDAS operate on files and expect you to specify a file name for one or more parameters. There are several types of special syntax that can be used with certain tasks when specifying file names. These syntax features include:

Wild card characters, often called templates:
These are used to specify multiple files using pattern matching techniques. The wild cards are:
- * Matches any number of characters, e.g., z*.c0h
- ? Matches any single character, e.g., z01x23x.c?h

When using wildcards with image-processing tasks, be sure to exclude the binary pixel files by ending your file name specification with an "h", for example: y*.??h

List files, often called @-files: A list file is an ASCII file that contains a list of file names, one per line. If the task supports the list file feature, you would type the name of your list file, preceded by the "@" character. Figure 2.4 shows an example of how @-files are built and used.

Image section specification: Tasks that work with image data will often let you specify that you want to work on only a small area of the image rather than the entire image. (See "Displaying Images" on page 26.) To specify an image section, specify the X axis range and the Y axis range in square brackets, for example: image.hhh[10:200,20:200]
Group specification: HST images are stored in a format known as GEIS multigroup format. This lets one file contain one or more sets of related data, such as images taken from different detectors or time-resolved spectra. Many STSDAS tasks will let you choose which of the groups in a multigroup image will be used. To specify a group, enclose its number in brackets, for example: imagefile.hhh[7]. A description of GEIS format is available on-line within STSDAS by typing help geis.
IRAF networking specification: IRAF is capable of reading and writing files to and from remote systems on a network. This is often used with tasks in the fitsio and toolbox.convfile packages. You must do some work to enable this feature, however, and this is described in an online help file that can be read by typing help networking. To specify that you want to use the IRAF networking feature, you will specify the remote host name followed by an exclamation point (!), followed by the file name. For example: ra!mta.

File Structures
Directory Specification
Specifying Files

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