Usefull tips for FORTRAN

Few tips for FORTRAN:

Get arguments from command line

character (len = 20) :: arg1
call getarg (1, arg1)
if (len_trim(arg1) == 0) then 
   print*,'No Arg1 provided' stop
endif
read (arg1, *) nsteps

In this example FORTRAN takes the first arguments and read as number of steps. Always use the warning if loop for multiple argument, sometimes one might miss to give inputs of one argument and it becomes difficult to debug the code.

Use bash shell command in FORTRAN

character (len = 1024) :: command
command = 'cp file1 folder1/'
call system ( trim(command))
In this example file1 is copied to folder1/

Print integer padded by zeros
Let say we would like to print 4 digit integer as

0001
0002
....
9999

only thing we have use a formatting string I4.4 and we are done.
Get number of lines in a data file

open(unit,file='filename')
nline = 0
do
    read (unit, *, end = 10)
    nlines = nlines + 1
end do
10 close(unit)

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