indenting Fortran

Using Common Editors

Several commonly available editors will automatically indent your source as you compose the code. Two of the most popular editors that will do so are vim(1) and emacs(1) (assuming you have current versions installed that were built using the most common options).

That is, those editors will automatically recognize your code as Fortran if the file suffix is .F, .F90, .f, or .f90 and will apply language-specific indenting rules as you create your code.

The editors can also be used to re-indent existing files:

vim(1)

Assuming vim(1) has been built with internal indenting (typically it is) To re-indent an entire file in the vim(1) editor, start editing the file and enter

gg=G

For more information on the "=" command enter

:help =

while in the vim(1) editor. If the indenting is incorrect for free-format source, look for the topic "free-format fortran in vim" and update your indent file.

To use vim(1) as a command to indent many files use

vim -T dumb -c 'set backup' -c 'argdo execute "normal gg=G"|w' -c 'q!' --not-a-term *.f90

if you want backup files for each file, or use

vim -T dumb  -c 'set nobackup nowritebackup noswapfile' -c 'argdo execute "normal gg=G"|w' -c 'q!' --not-a-term *.f90

if you do not need the backup files (and to make it run optimally).

emacs(1)

To use emacs(1) to indent free-format fortran files as a command create a small script file called indent_emacs:

#!/bin/bash
for FILENAME in $*
do
   emacs --batch $FILENAME -f mark-whole-buffer -f f90-indent-subprogram -f save-buffer
done

And then enter "chmod u+xr indent_emacs". Now you can use

./indent_emacs *.f90

to batch indent many files.

Programs

A Fortran indenter program named findent(1) can be used as a CLI (Command Line Interface) command, with a Java GUI interface, and from several editors such as vim.

Examples

Given the file

 program demo_expand
 !  test filter to expand escape sequences in input lines
 use M_strings, only : expand
 character(len=1024) :: line
 integer             :: ios
 READFILE: block
 do
 read(*,'(A)',iostat=ios)line
 if(ios /= 0) exit READFILE
 write(*,'(a)')trim(expand(line))
 enddo
 endblock READFILE
 end program demo_expand

Then the commands

findent <demo_expand.f90 >demo_expand.f90.new;mv demo_expand.f90.new demo_expand.f90

produces

program demo_expand
!  test filter to expand escape sequences in input lines
   use M_strings, only : expand
   character(len=1024) :: line
   integer             :: ios
   READFILE: block
      do
         read(*,'(A)',iostat=ios)line
         if(ios /= 0) exit READFILE
         write(*,'(a)')trim(expand(line))
      enddo
   endblock READFILE
end program demo_expand

And the command

vim -T dumb -c 'normal gg=G' -c w -c 'q!' --not-a-term xxx.f90

Produces

program demo_expand
        !  test filter to expand escape sequences in input lines
        use M_strings, only : expand
        character(len=1024) :: line
        integer             :: ios
        READFILE: block
                do
                read(*,'(A)',iostat=ios)line
                if(ios /= 0) exit READFILE
                write(*,'(a)')trim(expand(line))
                enddo
        endblock READFILE
end program demo_expand