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This is an old revision of CoreSyntax made by DavidLee on 2008-04-20 12:34:23.

 

Core Syntax

The core syntax for xmlsh was derived from the open source Shell Command Language syntax document. xmlsh does not follow this syntax exactly, but rather it was used as a basis.

Syntax Synopsis

This is a synopsis of the supported syntax. Complete specifications (will be) provided in the future when the language is stabilized.

Commands

A simple-command is a sequence of non-blank words separated
by blanks. The first word specifies the name of the command
to be executed. Except as specified below, the remaining
words are passed as arguments to the invoked command.
The command name is used to locate the command (builtin, nternal,external) . The
value of a simple-command.

A pipeline is a sequence of one or more commands separated
by |. The standard output of each command but the last is
connected by a Pipe to the standard input of the next
command. Each command is run as a separate thread (if builtin or internal)
or as a seperate process (if external). The
shell waits for the last command to terminate. The exit
status of a pipeline is the exit status of the last command
in the pipeline.
A list is a sequence of one or more pipelines separated by
;, &, &&, or
, and optionally terminated by ; or &. Of
these four symbols, ; and & have equal precedence, which is
lower than that of && and
. The symbols && and also
have equal precedence. A semicolon (;) causes sequential
execution of the preceding pipeline, that is, the shell
waits for the pipeline to finish before executing any com-
mands following the semicolon. An ampersand (&) causes asyn-
chronous execution of the preceding pipeline, that is, the
shell does not wait for that pipeline to finish. The symbol
&& (
) causes the list following it to be executed only if
the preceding pipeline returns a zero (non-zero) exit
status. An arbitrary number of newlines may appear in a
list, instead of semicolons, to delimit commands.
A command is either a simple-command or one of the follow-
ing. Unless otherwise stated, the value returned by a com-
mand is that of the last simple-command executed in the com-
mand.
for name [ in word ... ] do list done
Each time a for command is executed, name is set to the
next word taken from the in word list. If in word ... is
omitted, then the for command executes the do list once
for each positional parameter that is set (see Parameter
Substitution section below). Execution ends when there
are no more words in the list.


case word in [ pattern [ | pattern ] ) list ;; ] ... esac
A case command executes the list associated with the
first pattern that matches word. The form of the pat-
terns is the same as that used for file-name generation
(see File Name Generation section), except that a slash,
a leading dot, or a dot immediately following a slash
need not be matched explicitly.


if list ; then list ; [ elif list ; then list ; ] ... [ else list ; ] fi
The list following if is executed and, if it returns a zero
exit status, the list following the first then is executed.
Otherwise, the list following elif is executed and, if its
value is zero, the list following the next then is executed.
Failing that, the else list is executed. If no else list or
then list is executed, then the if command returns a zero
exit status.

while list do list done
A while command repeatedly executes the while list and,
if the exit status of the last command in the list is
zero, executes the do list; otherwise the loop terminates.
If no commands in the do list are executed,
then the while command returns a zero exit status;
until may be used in place of while to negate the loop
termination test.


(list)
Execute list in a sub-shell.
Hence changes to the environment made within this subshell do not affect the parent shell.
{ list;}
list is executed in the current (that is, parent)
shell. The { must be followed by a space.


name () { list;} NOT YET IMPLMENTED
Define a function which is referenced by name. The body
of the function is the list of commands between { and }.
The { must be followed by a space. Execution of func-
tions is described below (see Execution section).
The { and } are unnecessary if the body of the function
is a command as defined above, under Commands.


The following words are only recognized as the first word of
a command and when not quoted:
if then else elif fi case esac for while until do
done { }

Comments Lines
A word beginning with # causes that word and all the follow-
ing characters up to a newline to be ignored.

Variable Substitution
Words are scanned for $ which indicates variable substition.



Command Substitution
The shell reads commands from the string between $( and )
and the standard output from these commands may
be used as all or part of a word. Trailing newlines from the
standard output are removed.
No interpretation is done on the string before the string is
read, except to remove backslashes (\) used to escape other
characters.

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