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documentation for some grub-script features

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bvk.groups@gmail.com 2010-09-07 09:33:29 +05:30
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@ -1227,8 +1227,10 @@ The @samp{$} character retains its special meaning within double quotes.
The backslash retains its special meaning only when followed by one of the
following characters: @samp{$}, @samp{"}, @samp{\}, or newline. A
backslash-newline pair is treated as a line continuation (that is, it is
removed from the input stream and effectively ignored). A double quote may
be quoted within double quotes by preceding it with a backslash.
removed from the input stream and effectively ignored@footnote{Currently a
backslash-newline pair within a variable name is not handled properly, so
use this feature with some care.}). A double quote may be quoted within
double quotes by preceding it with a backslash.
@heading Variable expansion
@ -1240,11 +1242,15 @@ which could be interpreted as part of the name.
Normal variable names begin with an alphabetic character, followed by zero
or more alphanumeric characters.
Positional variable names consist of one or more digits. These are reserved
for future expansion.
Positional variable names consist of one or more digits. They represent
parameters passed to function calls, with @samp{$1} representing the first
parameter, and so on.
The special variable name @samp{?} expands to the exit status of the most
recently executed command.
recently executed command. When positional variable names are active, other
special variable names @samp{@@}, @samp{*} and @samp{#} are defined and they
expand to all positional parameters with necessary quoting, positional
parameters without any quoting, and positional parameter count respectively.
@heading Comments
@ -1305,6 +1311,45 @@ the body.
@xref{menuentry}.
@end table
@heading Built-in Commands
Some built-in commands are also provided by GRUB script to help script
writers perform actions that are otherwise not possible. For example, these
include commands to jump out of a loop without fully completing it, etc.
@table @asis
@item break [@code{n}]
Exit from within a @code{for}, @code{while}, or @code{until} loop. If
@code{n} is specified, break @code{n} levels. @code{n} must be greater than
or equal to 1. If @code{n} is greater than the number of enclosing loops,
all enclosing loops are exited. The return value is 0 unless @code{n} is
not greater than or equal to 1.
@item continue [@code{n}]
Resume the next iteration of the enclosing @code{for}, @code{while} or
@code{until} loop. If @code{n} is specified, resume at the @code{n}th
enclosing loop. @code{n} must be greater than or equal to 1. If @code{n}
is greater than the number of enclosing loops, the last enclosing loop (the
@dfn{top-level} loop) is resumed. The return value is 0 unless @code{n} is
not greater than or equal to 1.
@item return [@code{n}]
Causes a function to exit with the return value specified by @code{n}. If
@code{n} is omitted, the return status is that of the last command executed
in the function body. If used outside a function the return status is
false.
@item shift [@code{n}]
The positional parameters from @code{n}+1 @dots{} are renamed to
@code{$1}@dots. Parameters represented by the numbers @code{$#} down to
@code{$#}-@code{n}+1 are unset. @code{n} must be a non-negative number less
than or equal to @code{$#}. If @code{n} is 0, no parameters are changed.
If @code{n} is not given, it is assumed to be 1. If @code{n} is greater
than @code{$#}, the positional parameters are not changed. The return
status is greater than zero if @code{n} is greater than @code{$#} or less
than zero; otherwise 0.
@end table
@node Embedded configuration
@section Embedding a configuration file into GRUB