Procedure

     RDNBL ( Read non-blank line )

     SUBROUTINE RDNBL ( FILE, LINE, EOF )

Abstract

     Read the next non-blank line of text from a text file.

Required_Reading

     None.

Keywords

     FILES
     TEXT

Declarations

     IMPLICIT NONE

     CHARACTER*(*)       FILE
     CHARACTER*(*)       LINE
     LOGICAL             EOF

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     FILE       I   Input text file.
     LINE       O   Next non-blank line from the input text file.
     EOF        O   End-of-file indicator.

Detailed_Input

     FILE     is the name of the text file from which the next
              line is to be read. If the file is not currently
              open, it is opened with a logical unit determined
              at run time, and the first line of the file is
              returned. Otherwise, the next line not yet read
              from the file is read and returned.

Detailed_Output

     LINE     is next non-blank line of text in the specified file.

     EOF      is .TRUE. when the end of the file is reached, and is
              otherwise .FALSE.

Parameters

     None.

Exceptions

     1)  If either the end of the file is reached or an error occurs
         before a non-blank line is found, LINE is blank.

Files

     See input FILES.

Particulars

     RDNBL simply calls RDTEXT until one of two things happens:

        1. A non-blank line is found (in which case the line
           is returned).

        2. The end of the file is reached (in which case the
           file is closed, a blank line is returned, and the
           end-of-file indicator becomes .TRUE.)

Examples

     Let FILE.1 contain the following lines.

        Mary had a little lamb

        Everywhere that Mary went



        Its fleece was white as snow.
        The lamb was sure to go.

     Then the code fragment

        DO I = 1, 4
           CALL RDNBL ( 'FILE.1', LINE, EOF )
           WRITE (*,*) LINE
        END DO

     produces the following output:

        Mary had a little lamb
        Everywhere that Mary went
        Its fleece was white as snow.
        The lamb was sure to go.

     In fact, the following code fragment removes all of the blank
     lines from an arbitrary text file (FILE).

        CALL RDNBL ( FILE, LINE, EOF )

        DO WHILE ( .NOT. EOF )
           WRITE (*,*) LINE( : RTRIM(LINE) )

           CALL RDNBL ( FILE, LINE, EOF )
        END DO

     Note that because RDNBL calls RDTEXT, calls to either routine
     can be interspersed. For example, RDNBL can be used to skip
     blank lines at the beginning of the file, leaving the rest to
     be processed:

        CALL RDNBL ( FILE, LINE, EOF )

        DO WHILE ( .NOT. EOF )
           < do something with LINE >

           CALL RDTEXT ( FILE, LINE, EOF )
        END DO

Restrictions

     1)  Any restrictions that apply to RDTEXT apply to RDNBL as well.

Literature_References

     None.

Author_and_Institution

     J. Diaz del Rio    (ODC Space)
     I.M. Underwood     (JPL)

Version

    SPICELIB Version 1.1.0, 12-AUG-2021 (JDR)

        Added IMPLICIT NONE statement.

        Edited the header to comply with NAIF standard.

    SPICELIB Version 1.0.0, 07-AUG-1994 (IMU)