How to output (using the write statement) an apostrophe " ' "?

Question

I want to use system command in Fortran 90 for executing folowing command:

command =  awk '{print "C"NR,$1,$2,$3}' filename1 > filename2
call system(trim(command))

here my filename1 and filename2 are variables in a Fortran 90 program. But the problem is that any character can be assigned to a variable which are enclosed between apostrophes and my variable should also be consisting of apostrophes. I don't know how to type it in Fortran 90.

Answer 1

Just use two apostrophes in a row inside the string

command =  'awk ''{print "C"NR,$1,$2,$3}'' filename1 > filename2'

Additionally, because I did not notice filename1 and filename2 are variables, you must append them as chw21 shows:

 // trim(filename1)//' > '//trim(filename2)

Answer 2

You can try to use a parameter for single quotes, like this:

character, parameter :: sq = "'"

Then you can chain things together like this:

command = 'awk '//sq//'{print "C"NR,$1,$2,$3}'//sq//' '// &
           trim(filename1)//' > '//trim(filename2)

Or, you can swap between single- and double quoted strings:

command = "awk '" // '{print "C"NR,$1,$2,$3}' // "' " // &
           trim(filename1) // ' > ' // trim(filename2)

What you shouldn't do at all is using the Hollerith format instruction:

     write(command, 100) trim(f1), trim(f2)
100  FORMAT(29Hawk '{print "C"NR,$1,$2,$3}' , A, " > ", A)

That's why I'm not even telling you. Oh.