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Global Variables

Glish makes available to every script the following global variables:

pi

is an approximation of the mathematical constant $\pi$, which equals the area of a unit circle. This global variable approximates $\pi$ to 24 decimal places.

e

is an approximation of the mathematical constant e. The primary property of e is that if y = e^x, then ${\frac{dy}{dx}}$ = e^x. This global variable approximates e to 24 decimal places.

argv

is a list of the arguments (interpreted as string's) with which the Glish script was invoked. Presently the Glish interpreter is invoked with a filename to interpret followed by a list of arguments. So, for example, if a script is invoked using:

    glish script.g hello, how are you

then argv is a string value with 4 elements, ``hello,", ``how", ``are", and ``you".

environ

is a record providing access to the UNIX environment (i.e., what in C programs is accessible via getenv()). Each environment variable corresponds to a string-valued field in the record. For example,

    environ.HOME

returns the value of the $HOME environment variable. Naturally this can also be referred to using:

    environ["HOME"]

Changing the environ global does not presently affect the environment in which Glish clients are run (though it may in the future).

system

is an agent record that contains general information about the environment (not in an ``environment variable'' sense) in which the Glish script runs. It also generates events corresponding to changes in the environment.

The predefined fields of system are:

version

gives the version level of the Glish interpreter. Presently this field's type is string, though it may change to double in the future to facilitate inequality comparisons like ``system.version >= 2.1".

is_script_client

is true (T) if the Glish script is run as a script client (§ 7.10, page ) and false (F) if not.

print.limit

allows you to limit how much of Glish values is output to the screen (see § 5.3.2, page ).

print.precision

allows you to specify the number of significant digits to use in outputting floating point numbers (see § 5.3.1, page ).

tk

contains the Tk version number if the glishtk.g (see § 11.8, page ) client script with the Tk widgets is loaded.

path.include

path searched by include when attempting to include a file (see § 4.15, page ).

path.bin.host

path searched when starting clients on the machine host.

output.pager.exec

the executable to be started to handle paging of output, e.g. less or more.

output.pager.limit

the number of lines where paging begins. If set to 0, paging is always done; if set to -1, paging is never done.

output.log

place to log input and output. (See § 9.2, page .)

output.ilog

place to log input. (See § 9.2, page .)

output.olog

place to log output. (See § 9.2, page .)

output.pager.log

place to log input and output. (See § 9.2, page .)

pid

process id of the current Glish interpreter.

ppid

process id of the current Glish interpreter's parent process.

limits.max

contains the maximum values for Glish's builtin (non-boolean) numeric types.

limits.min

contains the minimum values for Glish's builtin (non-boolean) numeric types.

The events generated by system are:

connection_lost

indicates the loss of the network connection to a remote host. The value of the event names the remote host. (See § 16.2, page  for details as to when this event is generated.)

connection_restored

indicates the restoration of the network connection to a remote host. The value of the event names the remote host. See § 16.2, page  for details as to when this event is generated.

daemon_terminated

indicates that a remote glishd daemon terminated; normally this indicates a problem or bug (see § 16.2, page  for details as to when this event is generated).

For example, the following checkpoints some local data whenever the network connection to the ``frontend'' host drops, and rolls back to the checkpoint when connectivity resumes:

    whenever system->connection_lost do
        {
        if ( $value == "frontend" )
            do_local_checkpoint()
        }

    whenever system->connection_restored do
        {
        if ( $value == "frontend" )
            roll_back_to_checkpoint()
        }

script

has one of two possible values. If the Glish script is run as a client of another script, then script is an agent record (§ 7.2.2, page ) that can be used to receive events sent by the parent script and send events back to the parent (See § 7.10, page  for details). If the Glish script is running independently, then script is the boolean value F.