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6.1 Tokens

pspp divides most syntax file lines into series of short chunks called tokens. Tokens are then grouped to form commands, each of which tells pspp to take some action—read in data, write out data, perform a statistical procedure, etc. Each type of token is described below.

Identifiers
Identifiers are names that typically specify variables, commands, or subcommands. The first character in an identifier must be a letter, ‘#’, or ‘@’. The remaining characters in the identifier must be letters, digits, or one of the following special characters:
          
. _ $ # @

Identifiers may be any length, but only the first 64 bytes are significant. Identifiers are not case-sensitive: foobar, Foobar, FooBar, FOOBAR, and FoObaR are different representations of the same identifier.

Some identifiers are reserved. Reserved identifiers may not be used in any context besides those explicitly described in this manual. The reserved identifiers are:

          
ALL AND BY EQ GE GT LE LT NE NOT OR TO WITH

Keywords
Keywords are a subclass of identifiers that form a fixed part of command syntax. For example, command and subcommand names are keywords. Keywords may be abbreviated to their first 3 characters if this abbreviation is unambiguous. (Unique abbreviations of 3 or more characters are also accepted: ‘FRE’, ‘FREQ’, and ‘FREQUENCIES’ are equivalent when the last is a keyword.)

Reserved identifiers are always used as keywords. Other identifiers may be used both as keywords and as user-defined identifiers, such as variable names.

Numbers
Numbers are expressed in decimal. A decimal point is optional. Numbers may be expressed in scientific notation by adding ‘e’ and a base-10 exponent, so that ‘1.234e3’ has the value 1234. Here are some more examples of valid numbers:
          -5  3.14159265359  1e100  -.707  8945.

Negative numbers are expressed with a ‘-’ prefix. However, in situations where a literal ‘-’ token is expected, what appears to be a negative number is treated as ‘-’ followed by a positive number.

No white space is allowed within a number token, except for horizontal white space between ‘-’ and the rest of the number.

The last example above, ‘8945.’ will be interpreted as two tokens, ‘8945’ and ‘.’, if it is the last token on a line. See Forming commands of tokens.

Strings
Strings are literal sequences of characters enclosed in pairs of single quotes (‘'’) or double quotes (‘"’). To include the character used for quoting in the string, double it, e.g. ‘'it''s an apostrophe'’. White space and case of letters are significant inside strings.

Strings can be concatenated using ‘+’, so that ‘"a" + 'b' + 'c'’ is equivalent to ‘'abc'’. So that a long string may be broken across lines, a line break may precede or follow, or both precede and follow, the ‘+’. (However, an entirely blank line preceding or following the ‘+’ is interpreted as ending the current command.)

Strings may also be expressed as hexadecimal character values by prefixing the initial quote character by ‘x’ or ‘X’. Regardless of the syntax file or active dataset's encoding, the hexadecimal digits in the string are interpreted as Unicode characters in UTF-8 encoding.

Individual Unicode code points may also be expressed by specifying the hexadecimal code point number in single or double quotes preceded by ‘u’ or ‘U’. For example, Unicode code point U+1D11E, the musical G clef character, could be expressed as U'1D11E'. Invalid Unicode code points (above U+10FFFF or in between U+D800 and U+DFFF) are not allowed.

When strings are concatenated with ‘+’, each segment's prefix is considered individually. For example, 'The G clef symbol is:' + u"1d11e" + "." inserts a G clef symbol in the middle of an otherwise plain text string.

Punctuators and Operators
These tokens are the punctuators and operators:
          
, / = ( ) + - * / ** < <= <> > >= ~= & | .

Most of these appear within the syntax of commands, but the period (‘.’) punctuator is used only at the end of a command. It is a punctuator only as the last character on a line (except white space). When it is the last non-space character on a line, a period is not treated as part of another token, even if it would otherwise be part of, e.g., an identifier or a floating-point number.