### 18 Glossary

• Alias
A mechanism for abbreviating a C-shell command line.
• ARD
ASCII Region Definition. A syntax for specifying various regions of an image in a text file. Used for masking image data. It is described in SUN/183.
• awk
A pattern-scanning and text-processing language. In other words it is a programmable report generator. Its name comes from the initials of the authors.
• CONVERT
A Starlink utility package for converting between NDF and various data formats such as FITS. It is described in SUN/55.
• Current process
The task currently running the shell (in the context of this document). C-shell scripts invoked from the current process are each run in new (child) processes.
• Environment variable
A global variable to define the characteristics of a UNIX environment such as the terminal type or home directory. It is defined with the setenv command. By convention, environment variables appear in uppercase. Environment variables are often used to refer to a directory or to tune software.
• Figaro
A general astronomical data-reduction package but concentrating on spectroscopy. It is available in several flavours. The Starlink version is described in SUN/86.
• File modifier
Syntax for specifying a part of a filename. They appear following a filename and have the form colon followed by a letter. For example, :t excludes the path.
• FITS
Flexible Image Transport System (FITS). The most commonly used format for astronomical data storage. It comprises a series of text headers followed by image or tabular data.
• HDS
Hierarchical Data System. The underlying data system for Starlink data files. It is used to create and access NDF datasets.
• KAPPA
The Starlink Kernel Application Package. A suite of facilities for processing and viewing astronomical images. Described in SUN/95.
• Match
A string in a file that is successfully specified by a regular expression. It is also a filename, shell variable, or alias successfully specified by wildcards within the shell.
• Metacharacter
Characters which have special meanings. For the shell these include wildcards, quotes, and logical operators. In regular expressions, metacharacters are used to specify strings to match.
• NDF
The standard Starlink data-storage format. An hierarchical format for multi-dimensional data storage. Accessed using libraries supported by Starlink. Use of NDF is described in SUN/33.
• NDF Section
A subset or superset of a dataset (originally applied to just NDFs) defined by specifying the pixel bounds or co-ordinate limits along each axis following the dataset’s name. See SUN/95’s chapter called “NDF Sections” for a description and many examples.
• Output parameters
A channel through which some Starlink applications write their results. These tend to be applications that do not create an output dataset, such as statistics and dataset attributes. They are sometimes called “Results parameters”. For examples see Section 9.
• Path
A list of directories which the system searches in turn to resolve command requests.
• Pipe, piping
Mechanism by which the standard output of one programme is passed to the standard input of another. It allows sophisticated tools to be made from simple commands. The | character represents the pipe.
• Process
A task being performed by the computer.
• Process identification number
A positive integer that uniquely identifies a process within the system.
• Regular expression
A pattern of characters used to match against the same characters in a search. They usually include special characters, which represent things other than themselves, to refine the search. Regular expressions empower utilities like grep, sed and awk. Although similar to shell wildcards there are differences, so be careful.
• sed
The stream editor. It is useful for editing large files or applying the same edits to a series of files.
• Shell
A programme that listens to your terminal, and accepts and interprets the commands you type. There are several UNIX shells including the Bourne (sh), Bourne-again (bash), Korn (ksh), as well as the C shell (csh).
• Shell variable
An identifier that can store one or more strings. Variables enable string processing, and integer and logical expressions in the shell. See Section 7 for more details.
• Standard input
The file from which most UNIX programmes read their input data. It defaults to the terminal if you do not supply the input on the command line or a file.
• Standard output
File to which most UNIX programmes output their results. Text output from Starlink applications are also routed there. Standard output defaults to your terminal. It can be piped into commands that accept standard input.
 Wildcard expression Matches * Zero or more characters ? Exactly one character [xyz] One character in the set x, y, or z [a-m] One character in the range from a to m [A-Za-z] All alphabetic characters [0-9] All numeric characters {alpha,beta,a,b} A set of options, alpha, beta, a, or b {aa,bb[1-3]} aa, bb1, bb2, or bb3