C Library Functions - readenv (3)

NAME

readenv(3f) - [M_io:QUERY] a function returning the value of an environment variable (LICENSE:PD)

Syntax
Description
Options
Returns
Example
See Also
Author
License

SYNTAX

function readenv(NAME,DEFAULT,IERR=IERR) result(VALUE)

    character(len=*),intent(in)          :: NAME
    character(len=*),intent(in),optional :: DEFAULT
    integer,intent(out),optional         :: IERR
    character(len=:),allocatable         :: VALUE

     or

    character(len=*),intent(in)          :: NAME
    real,intent(in),optional             :: DEFAULT
    integer,intent(out),optional         :: IERR
    real                                 :: VALUE

     or

    character(len=*),intent(in)          :: NAME
    integer,intent(in),optional          :: DEFAULT
    integer,intent(out),optional         :: IERR
    integer                              :: VALUE

     or

    character(len=*),intent(in)          :: NAME
    doubleprecision,intent(in),optional  :: DEFAULT
    integer,intent(out),optional         :: IERR
    doubleprecision                      :: VALUE
     or

    character(len=*),intent(in)          :: NAME
    logical,intent(in),optional          :: DEFAULT
    integer,intent(out),optional         :: IERR
    logical                              :: VALUE

DESCRIPTION

Get the value of an environment variable or optionally return a default value if the returned value would be a blank string.
The type returned is the same as the type of the default

OPTIONS

NAME name of environment variable

DEFAULT
value to return if environment variable is not set or set to an empty string. May be CHARACTER, REAL, INTEGER, or DOUBLEPRECISION. Defaults to a null CHARACTER value.

RETURNS

VALUE the value of the environment variable or the default. The type is the same as DEFAULT. If an error occurs and it is numeric, huge(0|0.0|0.0d0) is returned.
For a LOGICAL type, Any environment variable value starting with F,f,N or n is .FALSE. and any value starting with Y,y,T or t is true. A leading period (".") is ignored. Anything else returns .false. .

IERR return error code. Must be specified with a keyword. It is zero if no error occurred.

EXAMPLE

Sample program:

   program demo_readenv
   use M_io, only : readenv, getname
   character(len=*),parameter :: g=’(*(g0))’
   integer :: ierr

      if(readenv(’STOP’).eq.’RUN’)then
         write(*,g)repeat(’-’,80)
         write(*,g)readenv(’CHARACTER’,’string’)
         write(*,g)readenv(’INTEGER’,100)
         write(*,g)readenv(’REAL’,200.0)
         write(*,g)readenv(’DOUBLE’,300.0d0)
         write(*,g)readenv(’LOGICAL’,.true.)

         write(*,g)repeat(’-’,80)
         write(*,g)readenv(’CHARACTER’,’string’,ierr=ierr)
         write(*,*)’ierr=’,ierr
         write(*,g)readenv(’INTEGER’,100,ierr=ierr)
         write(*,*)’ierr=’,ierr
         write(*,g)readenv(’REAL’,200.0,ierr=ierr)
         write(*,*)’ierr=’,ierr
         write(*,g)readenv(’DOUBLE’,300.0d0,ierr=ierr)
         write(*,*)’ierr=’,ierr
         write(*,g)readenv(’LOGICAL’,.true.)
         write(*,*)’ierr=’,ierr

         write(*,g)repeat(’-’,80)
         write(*,g)readenv(’CHARACTER’)
         write(*,g)readenv(’HOME’)
       else
         write(*,g)repeat(’-’,80)
         call execute_command_line(’env STOP=RUN ’//getname())
         call execute_command_line(’env STOP=RUN CHARACTER=aaaa &
         & INTEGER=1 REAL=2.3 DOUBLE=444444444444 ’//getname())
         call execute_command_line(’env STOP=RUN CHARACTER=bbbb &
         & INTEGER=1 REAL=2.3 DOUBLE=44.555 ’//getname())
         call execute_command_line(’env STOP=RUN CHARACTER=cccc &
         & INTEGER=asdf REAL=asdf DOUBLE=adsf ’//getname())
         write(*,g)repeat(’-’,80)
         stop
      endif

   end program demo_readenv

AUTHOR

John S. Urban

LICENSE

Public Domain

Nemo Release 3.1

readenv (3)

February 23, 2025

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