env.gex - GrADS Extensions for Environment Variable Manipulation

NAME

env.gex - GrADS Extensions for Environment Variable Manipulation

SYNOPSIS

GrADS Commands:

env CMD - Expands environment variables in CMD and executes it

getenv NAME - Print value of NAME

setenv NAME VALUE - Set environment variable NAME to VALUE

printenv STRING - Expands all environment variables in <STRING>

GrADS Scripting Language Functions:

getenv(NAME) - Return value of environment variable NAME

setenv(NAME,VALUE) - Set environment variable NAME to VALUE

printenv(STRING) - Return string with expansion of all environment variables in <STRING>

DESCRIPTION

This library implements GrADS extensions (gex) with commands for setting and retriving environment variables. In addition it can exapand all environment variables in a GrADS command string and then execute the command after the expansion takes places. These features are available at the GrADS prompt or as GrADS Scription Language functions.

Environment variables can be used in GrADS in a variety of ways. Prior to starting GrADS you can set up environment variables with the locations of your data directories and use this environment variable when opening your files, for example. Another useful application is for holding truly global information which persists throughout the extent of your GrADS session. You can use this technique for communicating between GrADS scripts that are invoked from different run commands.

EXAMPLES

Using getenv to print the value of a list of environment variables

   ga-> getenv USER HOME TMPDIR
   Environment variable USER = dasilva
   Environment variable HOME = /Users/dasilva
   Environment variable TMPDIR = <undef>

Notice that environment variable TMPDIR was not defined in this case.

Using setenv to set the value of a given environment variable

   ga-> setenv OPENGRADS /share/dasilva/opengrads
   Environment variable OPENGRADS = /share/dasilva/opengrads

Using printenv expand environment variables in a string

   ga-> printenv $HOME/src/grads/test_data
   /Users/dasilva/src/grads/test_data

Notice that undefined variables exapand to a blank string:

   ga-> printenv Undefined variable FOO = <$FOO>
   Undefined variable FOO = <>

Get the process id (PID) for creating temporary files, etc

   ga-> printenv /tmp/tempfile.$$
   /tmp/tempfile.21386

Using env to expand environment variables, then execute a GrADS command

  ga-> env open $OPENGRADS/test_data/model.ctl

Notice that you can use @ as a short hand for env:

  ga-> @ open $OPENGRADS/test_data/model.ctl

Setting environment variables based on another env variable

Using the @ short-hand for env:

   ga-> @ setenv FILE $HOME/data/model.ctl
   setenv FILE /Users/dasilva/data/model.ctl
   Environment variable FILE = /Users/dasilva/data/model.ctl
   ga-> @ open $FILE
   open /Users/dasilva/data/model.ctl
   Scanning description file: /Users/dasilva/data/model.ctl
   Data file /Users/dasilva/data/model.grb is open as file 1
   LON set to 0 360
   LAT set to -90 90
   LEV set to 1000 1000
   Time values set: 1987:1:1:0 1987:1:1:0

Saving complicated expressions in environment variables (like aliases)

You can use env variables to save long expressions:

   ga-> setenv EXPR ua;va;sqrt(ua*ua+va*va)
   Environment variable EXPR = ua;va;sqrt(ua*ua+va*va)
   ga-> @ display $EXPR
   display ua;va;sqrt(ua*ua+va*va)

COMMANDS PROVIDED

The following commands are loosely based on the C-Shell syntax:

env CMD

This command expands environment variables in string CMD and executes it as a GrADS command after expansion. Example:

   ga-> env open $HOME/data/model.ctl
   open /Users/dasilva/data/model.ctl
   Scanning description file: /Users/dasilva/data/model.ctl
   Data file /Users/dasilva/data/model.grb is open as file 1
   LON set to 0 360
   LAT set to -90 90
   LEV set to 1000 1000
   Time values set: 1987:1:1:0 1987:1:1:0

getenv NAMEs

This command takes a list of environment variables and prints the value of each one. Example:

   ga-> getenv USER HOME DISPLAY
   Environment variable USER = dasilva
   Environment variable HOME = /Users/dasilva
   Environment variable DISPLAY = :0.0

setenv NAME VALUE

This command sets environment variable NAME to VALUE. Example:

   ga-> setenv DATADIR /archive/data
   Environment variable DATADIR = /archive/data

printenv STRING

This command expands all environment variables in STRING, printing the result to the screeen. Example:

   ga-> printenv My home directory is $HOME
   My home directory is /Users/dasilva

xenv STRING

Same as printenv.

@ STRING

Same as env.

SEE ALSO

AUTHOR

Arlindo da Silva (dasilva@opengrads.org)

COPYRIGHT

Copyright (C) 2007-2008 Arlindo da Silva; All Rights Reserved.

This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

 env.gex - GrADS Extensions for Environment Variable Manipulation