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How to add shell command to Fortran script

Is it possible to call a shell command from a Fortran script file?

My problem is that I am parsing really large files. These files have many lines, eg. 84084002 or similar. I need to know how many lines a file has before I start parsing, so I usually used the shell command: wc -l "filename"

and then used that number as a single variable parameter in my script.

But I would like to call this command from my program and use the number of lines and store it in the value of a variable.

I know it might not work, but if it does, please let me know.

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Since 1984, actually in the 2008 standard, but already implemented by most of the commonly encountered Fortran compilers, including gfortran

, there is a standard internal subroutine execute_command_line

that roughly corresponds to what is widely implemented, the standard subroutine system

. Since @MarkSetchell has (almost) written, you can try

CALL execute_command_line('wc -l < file.txt > wc.txt' ) 
OPEN(unit=nn,file='wc.txt') 
READ(nn,*) count


What Fortran doesn't have is a standard way to get the number of lines in a file without going through an operating system-specific workaround. Other, that is, than opening a file, counting the number of lines, and then rewinding to the beginning of the file to start reading.

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You should do something like this (untested - and I haven't written FORTRAN since 1984):



command='wc -l < file.txt > wc.txt' 
CALL system(command) 
OPEN(unit=nn,file='wc.txt') 
READ(nn,*) count
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