Accessing Named Files

The OPEN statement's FILE= specifier establishes the association of a logical unit to a named, physical file at runtime. This file can be pre-existing or created by the program. See the Sun FORTRAN 77 Language Reference Manual for a full discussion of the OPEN statement.

The FILE= specifier on an OPEN statement may specify a simple file name (FILE='myfile.out') or a file name preceded by an absolute or relative directory path (FILE='../Amber/Qproj/myfile.out'). Also, the specifier may be a character constant, variable, or character expression.

Library routines can be used to bring command-line arguments and environment variables into the program as character variables for use as file names in OPEN statements. (See man page entries for getarg(3F) and getenv(3F) for details; these and other useful library routines are also described in the Fortran Library Reference).

The following example (GetFilNam.f) shows one way to construct an absolute path file name from a typed-in name. The program uses the library routines GETENV, LNBLNK, and GETCWD to return the value of the $HOME environment variable, find the last non-blank in the string, and determine the current working directory:

      CHARACTER F*128, FN*128, FULLNAME*128
      PRINT*, 'ENTER FILE NAME:'
      READ *, F 
      FN = FULLNAME( F ) 
      PRINT *, 'PATH IS: ',FN
      END 

      CHARACTER*128 FUNCTION FULLNAME( NAME ) 
      CHARACTER NAME*(*), PREFIX*128
C          This assumes C shell.
C           Leave absolute path names unchanged. 
C           If name starts with '~/', replace tilde with home 
C           directory; otherwise prefix relative path name with 
C           path to current directory. 
      IF ( NAME(1:1) .EQ. '/' ) THEN 
            FULLNAME = NAME 
      ELSE IF ( NAME(1:2) .EQ. '~/' ) THEN 
            CALL GETENV( 'HOME', PREFIX ) 
            FULLNAME = PREFIX(:LNBLNK(PREFIX)) // 
&                         NAME(2:LNBLNK(NAME)) 
      ELSE 
            CALL GETCWD( PREFIX ) 
            FULLNAME = PREFIX(:LNBLNK(PREFIX)) // 
&                         '/' // NAME(:LNBLNK(NAME)) 
      ENDIF 
      RETURN 
      END

Compiling and running GetFilNam.f results in:

demo% pwd
/home/users/auser/subdir
demo% f77 -silent -o getfil GetFilNam.f
demo% getfil
anyfile
/home/users/auser/subdir/anyfile
demo%