passing values to interactive fortran program using echo command

Question

A fortran program requires three inputs to be passed interactively:

First input is just letter "D", second input is a file "A.cpt", and third input is a name for the output file that can be for example "B.out".

I have been trying to use echo command, but it is not working:

echo "D\nA.cpt\nB.out" | ./fortran_program

Any ideas?

UPDATE:

When using EOF, as suggested below, the program is going to an infinite loop repeating the following lines:

Please try again!
Please enter input binary hydra/quanta plot (old) filename
defaults <dotsurface_0_165.qpt> ext:<.qpt> (abort by EXIT or ^D) :  Sorry unable to open file: D.qpt
               or file: D
Please try again!
Please enter input binary hydra/quanta plot (old) filename
defaults <dotsurface_0_165.qpt> ext:<.qpt> (abort by EXIT or ^D) :  Sorry unable to open file: D.qpt

The source code for this program is on Github if that helps:

https://github.com/osmart/hole2/blob/master/src/qpt_conv.f

Would the intrinsic function get_command_argument work for your needs, or is it necessary to use (bash)? — Matt P
– Matt P, Commented Jul 16, 2019 at 4:57
When typing D, the program then expects a filename as the next argument. input, for instance, for the file input.qpt. Your second argument being A, the program looks for the file A.qpt. — Pierre de Buyl
– Pierre de Buyl, Commented Jul 16, 2019 at 8:47

roygvib · Accepted Answer · 2019-07-12 22:54:11Z

4

If you are using bash (or similar), I think echo -e or printf will be useful (but please check this page also). For example, either of

echo -e "D\nA.cpt\nB.out" | ./a.out
printf "D\nA.cpt\nB.out" | ./a.out

gives

str(1) = D         
str(2) = A.cpt     
str(3) = B.out

(for a.out generated from test.f90 below). Another approach may be to use "here document", e.g.

./a.out <<EOF
D
A.cpt
B.out
EOF

which I often use in a bash script (because the input part becomes more readable and looks like a separate input file).

!! test.f90
program main
    implicit none
    character(10) :: str( 3 )

    read *, str( 1 )
    read *, str( 2 )
    read *, str( 3 )

    print *, "str(1) = ", str(1)
    print *, "str(2) = ", str(2)
    print *, "str(3) = ", str(3)
end

edited Jul 12, 2019 at 22:54

answered Jul 12, 2019 at 22:41

roygvib

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Pierre de Buyl · Accepted Answer · 2019-07-14 08:25:25Z

0

Alternatively, you can use actual line breaks in the echo command:

user@host$ echo "1                             
2
3" | ./test_echo 
           1           2           3
user@host$

When you type "enter" after echo "1, you can keep on entering the quote-delimited string.

answered Jul 14, 2019 at 8:25

Pierre de Buyl

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