gsh/doc/variables.md

Variables

Model

GSH use the same model as declared in POSIX Shell. So you can refer to that documentation for operation like setting, unsetting and exporting variables.

Windows Specificities

The main difference when handling variables is that on Windows OS variables are not case sensitive whereas in POSIX Shell standard they are.

Variable existence

When doing:

echo $A_Variable

GSH will do the following:

1- Check if A_Variable exists in GSH internal state with specified casing 2- If A_Variable does not exist check the existence of A_VARIABLE and if value if coming from Windows environment. 3- If both previous existence checks fail then consider the variable as non existant.

Thus the following command launched for example from a Cygwin shell:

A_VARIABLE='upper' gsh.exe -c 'echo $A_Variable'

Will output:

upper

Inside the shell a similar command will have a different effect:

gsh.exe -c 'A_VARIABLE="upper"; echo $A_Variable'

Will output just a newline.

To summarize inside GSH variables behave as expected in a POSIX Shell but variables coming from the process environment are seen by all variables that differ just by casing.

Import/Export of Environment

During the initialisation of the GSH state, the process environment is imported the following way:

1- Import all environments variables into the shell state 2- For environment variables, if the upper case version of that variable is not in the environment create an entry for the upper case version of that variable.

During export of environment to external process the following actions are done:

1- Add at the beginning of the environment all upper case variables 2- Append to that environment all other variables from the shell state

These methods for import/export of environment ensure that:

1- GSH processes can pass between each other the full shell environment (case sensitive) 2- Interaction with other processes is intuitive

For example if from a CMD Windows shell the following is done:

 $ set My_Path=c:/tmp
 $ gsh -c "echo $MY_PATH"

Then the following will be displayed:

 c:/tmp

If from a GSH interactive shell the following commands are executed:

 $ export DUMMY=value1
 $ export Dummy=value2
 $ gsh -c 'echo $DUMMY; echo $Dummy'

The the following will be displayed:

 value1
 value2

Note that Cygwin use a similar mechanism, thus when spawning GSH from a Cygwin process should preserve all the variables even if only casing differ.

Special Variables

The PATH and HOME variables are automatically transform back and forth to a UNIX friendly representation (with /).