Wydawca
	Release Submission Daemon	Sergey Poznyakoff

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4.1.3 Statements

A simple statement consists of a keyword and value separated by any amount of whitespace. Simple statement is terminated with a semicolon (‘;’).

Examples of simple statements:

daemon yes;
pidfile /var/run/wydawca.pid;

A keyword begins with a letter and may contain letters, decimal digits, underscores (‘_’) and dashes (‘-’). Examples of keywords are: ‘group’, ‘file-sweep-time’.

A value can be one of the following:

number

A number is a sequence of decimal digits.

boolean

A boolean value is one of the following: ‘yes’, ‘true’, ‘t’ or ‘1’, meaning true, and ‘no’, ‘false’, ‘nil’, ‘0’ meaning false.

unquoted string

An unquoted string may contain letters, digits, and any of the following characters: ‘_’, ‘-’, ‘.’, ‘/’, ‘@’, ‘*’, ‘:’.

quoted string

A quoted string is any sequence of characters enclosed in double-quotes (‘"’). A backslash appearing within a quoted string introduces an escape sequence, which is replaced with a single character according to the following rules:

Sequence	Replaced with
\a	Audible bell character (ASCII 7)
\b	Backspace character (ASCII 8)
\f	Form-feed character (ASCII 12)
\n	Newline character (ASCII 10)
\r	Carriage return character (ASCII 13)
\t	Horizontal tabulation character (ASCII 9)
\v	Vertical tabulation character (ASCII 11)
\\	A single backslash (‘\’)
\"	A double-quote.

Table 4.1: Backslash escapes

In addition, the sequence ‘\newline’ is removed from the string. This allows to split long strings over several physical lines, e.g.:

"a long string may be\
 split over several lines"

If the character following a backslash is not one of those specified above, the backslash is ignored and a warning is issued.

Two or more adjacent quoted strings are concatenated, which gives another way to split long strings over several lines to improve readability. The following fragment produces the same result as the example above:

"a long string may be"
" split over several lines"

Depending on the context, the quoted string may be subject to variable expansion.

During variable expansion, references to variables in the string are replaced with their actual values. A variable reference has two basic forms:

  $v
  ${v}

where v is the variable name. The notation in curly braces serves several purposes. First, it should be used if the variable reference is immediately followed by an alphanumeric symbol, which will otherwise be considered part of it (as in ‘${home}dir’). Secondly, this form allows for specifying the action to take if the variable is undefined or expands to an empty value.

The following special forms are recognized:

${variable:-word}

Use Default Values. If variable is unset or null, the expansion of word is substituted. Otherwise, the value of variable is substituted.

${variable:=word}

Assign Default Values. If variable is unset or null, the expansion of word is assigned to variable. The value of variable is then substituted.

The assigned value remains in effet during expansion of the current string.

${variable:?word}

Display Error if Null or Unset. If variable is null or unset, the expansion of word (or a message to that effect if word is not present) is output to the current logging channel. Otherwise, the value of variable is substituted.

${variable:+word}

Use Alternate Value. If variable is null or unset, nothing is substituted, otherwise the expansion of word is substituted.

These constructs test for a variable that is unset or null. Omitting the colon results in a test only for a variable that is unset.

If a string contains a reference to an undefined variable, wydawca will report an error and abort. To gracefully handle such cases, use the default value construct, defined above.

Here-document

A here-document is a special construct that allows to introduce strings of text containing embedded newlines.

The <<word construct instructs the parser to read all the following lines up to the line containing only word, with possible trailing blanks. Any lines thus read are concatenated together into a single string. For example:

<<EOT
A multiline
string
EOT

Body of a here-document is interpreted the same way as double-quoted string, unless word is preceded by a backslash (e.g. ‘<<\EOT’) or enclosed in double-quotes, in which case the text is read as is, without interpretation of escape sequences.

If word is prefixed with - (a dash), then all leading tab characters are stripped from input lines and the line containing word. Furthermore, if - is followed by a single space, all leading whitespace is stripped from them. This allows to indent here-documents in a natural fashion. For example:

<<- TEXT
    All leading whitespace will be
    ignored when reading these lines.
TEXT

It is important that the terminating delimiter be the only token on its line. The only exception to this rule is allowed if a here-document appears as the last element of a statement. In this case a semicolon can be placed on the same line with its terminating delimiter, as in:

help-text <<-EOT
        A sample help text.
EOT;

list

A list is a comma-separated list of values. Lists are enclosed in parentheses. The following example shows a statement whose value is a list of strings:

alias (test,null);

In any case where a list is appropriate, a single value is allowed without being a member of a list: it is equivalent to a list with a single member. This means that, e.g.

alias test;

is equivalent to

alias (test);

time interval specification

The time interval specification is a string that defines an interval, much the same way we do this in English: it consists of one or more pairs ‘number’-‘time unit’. For example, the following are valid interval specifications:

"1 hour"
"2 hours 35 seconds"
"1 year 7 months 2 weeks 2 days 11 hours 12 seconds"

The pairs can occur in any order, however unusual it may sound to a human ear, e.g. ‘2 days 1 year’. If the ‘time unit’ is omitted, seconds are supposed.

A block statement introduces a logical group of statements. It consists of a keyword, followed by an optional value, and a sequence of statements enclosed in curly braces, as shown in the example below:

spool download {
  source /home/ftp/incoming/ftp;
  destination /home/ftp/pub;
}

The closing curly brace may be followed by a semicolon, although this is not required.