Save command line output to variable in Fortran
2
Is there a way to store the output of a command line utility to a variable in Fortran?
I have a BASH based utility which gives me a number which needs to be used in a Fortran program. I want to call the utility through the program itself, and avoid writing the output to a file if possible.
Something like this maybe?
integer a
write(a,*) call execute_command_line('echo 5')
Or like this maybe?
read(call execute_command_line('echo 5'),*) a
I don't think either of these is right though. I would like to know if there is actually a method to do this. I read the docs for execute_command_line but I don't think there is an output argument for the subroutine which does this.
fortran gfortran
asked Nov 23 '18 at 13:32
Yuki.kuroshita
16910
|
show 2 more comments
2
Is there a way to store the output of a command line utility to a variable in Fortran?
I have a BASH based utility which gives me a number which needs to be used in a Fortran program. I want to call the utility through the program itself, and avoid writing the output to a file if possible.
Something like this maybe?
integer a
write(a,*) call execute_command_line('echo 5')
Or like this maybe?
read(call execute_command_line('echo 5'),*) a
I don't think either of these is right though. I would like to know if there is actually a method to do this. I read the docs for execute_command_line but I don't think there is an output argument for the subroutine which does this.
fortran gfortran
asked Nov 23 '18 at 13:32
Yuki.kuroshita
16910
1
You'll have to use a temporary "file". I can't immediately find a question which I thought covered this, but some discussion is in this one.
– francescalus
Nov 23 '18 at 13:53
I have been trying and failing to make the fortranposix library mentioned in the question (an fPIC error for an object file which is not there in the Makefile). While I am figuring it out, is there any other library which adds posix functionalities like popen to Fortran? Or any other way which does not depend on external, non default libraries? @francescalus
– Yuki.kuroshita
Nov 23 '18 at 15:20
Some compilers bundle POSIX-like things in their runtime, so you may have luck there. But, to be honest, I'd just write standard output of the command to a real file and read it from my Fortran program.
– francescalus
Nov 23 '18 at 15:22
Thing is, this will go into a program for differential evolution with millions of generations, with 40 models, each with 4 model parameters, looped over 120 data points, so total iterations would be 19200000000 at max. I don't know if writing to a file and then reading from it each time would be the best thing to do here. The whole point of writing a differential evolution algorithm is to make things faster. I would have preferred to not have to read and write a file in each iteration
– Yuki.kuroshita
Nov 23 '18 at 15:33
2
This article about named pipes is interesting networkworld.com/article/3251853/linux/… (which says that everything is performed on memory. But I wonder whether a huge number of system calls background is no problem or have some practical issue...)
– roygvib
Nov 23 '18 at 19:47
|
show 2 more comments
2
2
2
2
Is there a way to store the output of a command line utility to a variable in Fortran?
I have a BASH based utility which gives me a number which needs to be used in a Fortran program. I want to call the utility through the program itself, and avoid writing the output to a file if possible.
Something like this maybe?
integer a
write(a,*) call execute_command_line('echo 5')
Or like this maybe?
read(call execute_command_line('echo 5'),*) a
I don't think either of these is right though. I would like to know if there is actually a method to do this. I read the docs for execute_command_line but I don't think there is an output argument for the subroutine which does this.
fortran gfortran
asked Nov 23 '18 at 13:32
Yuki.kuroshita
16910
Is there a way to store the output of a command line utility to a variable in Fortran?
I have a BASH based utility which gives me a number which needs to be used in a Fortran program. I want to call the utility through the program itself, and avoid writing the output to a file if possible.
Something like this maybe?
integer a
write(a,*) call execute_command_line('echo 5')
Or like this maybe?
read(call execute_command_line('echo 5'),*) a
I don't think either of these is right though. I would like to know if there is actually a method to do this. I read the docs for execute_command_line but I don't think there is an output argument for the subroutine which does this.
fortran gfortran
fortran gfortran
asked Nov 23 '18 at 13:32
Yuki.kuroshita
16910
asked Nov 23 '18 at 13:32
Yuki.kuroshita
16910
asked Nov 23 '18 at 13:32
Yuki.kuroshita
16910
asked Nov 23 '18 at 13:32
Yuki.kuroshita
16910
asked Nov 23 '18 at 13:32
Yuki.kuroshita
16910
16910
1
You'll have to use a temporary "file". I can't immediately find a question which I thought covered this, but some discussion is in this one.
– francescalus
Nov 23 '18 at 13:53
I have been trying and failing to make the fortranposix library mentioned in the question (an fPIC error for an object file which is not there in the Makefile). While I am figuring it out, is there any other library which adds posix functionalities like popen to Fortran? Or any other way which does not depend on external, non default libraries? @francescalus
– Yuki.kuroshita
Nov 23 '18 at 15:20
Some compilers bundle POSIX-like things in their runtime, so you may have luck there. But, to be honest, I'd just write standard output of the command to a real file and read it from my Fortran program.
– francescalus
Nov 23 '18 at 15:22
Thing is, this will go into a program for differential evolution with millions of generations, with 40 models, each with 4 model parameters, looped over 120 data points, so total iterations would be 19200000000 at max. I don't know if writing to a file and then reading from it each time would be the best thing to do here. The whole point of writing a differential evolution algorithm is to make things faster. I would have preferred to not have to read and write a file in each iteration
– Yuki.kuroshita
Nov 23 '18 at 15:33
2
This article about named pipes is interesting networkworld.com/article/3251853/linux/… (which says that everything is performed on memory. But I wonder whether a huge number of system calls background is no problem or have some practical issue...)
– roygvib
Nov 23 '18 at 19:47
|
show 2 more comments
1
You'll have to use a temporary "file". I can't immediately find a question which I thought covered this, but some discussion is in this one.
– francescalus
Nov 23 '18 at 13:53
I have been trying and failing to make the fortranposix library mentioned in the question (an fPIC error for an object file which is not there in the Makefile). While I am figuring it out, is there any other library which adds posix functionalities like popen to Fortran? Or any other way which does not depend on external, non default libraries? @francescalus
– Yuki.kuroshita
Nov 23 '18 at 15:20
Some compilers bundle POSIX-like things in their runtime, so you may have luck there. But, to be honest, I'd just write standard output of the command to a real file and read it from my Fortran program.
– francescalus
Nov 23 '18 at 15:22
Thing is, this will go into a program for differential evolution with millions of generations, with 40 models, each with 4 model parameters, looped over 120 data points, so total iterations would be 19200000000 at max. I don't know if writing to a file and then reading from it each time would be the best thing to do here. The whole point of writing a differential evolution algorithm is to make things faster. I would have preferred to not have to read and write a file in each iteration
– Yuki.kuroshita
Nov 23 '18 at 15:33
2
This article about named pipes is interesting networkworld.com/article/3251853/linux/… (which says that everything is performed on memory. But I wonder whether a huge number of system calls background is no problem or have some practical issue...)
– roygvib
Nov 23 '18 at 19:47
1
1
You'll have to use a temporary "file". I can't immediately find a question which I thought covered this, but some discussion is in this one.
– francescalus
Nov 23 '18 at 13:53
You'll have to use a temporary "file". I can't immediately find a question which I thought covered this, but some discussion is in this one.
– francescalus
Nov 23 '18 at 13:53
I have been trying and failing to make the fortranposix library mentioned in the question (an fPIC error for an object file which is not there in the Makefile). While I am figuring it out, is there any other library which adds posix functionalities like popen to Fortran? Or any other way which does not depend on external, non default libraries? @francescalus
– Yuki.kuroshita
Nov 23 '18 at 15:20
I have been trying and failing to make the fortranposix library mentioned in the question (an fPIC error for an object file which is not there in the Makefile). While I am figuring it out, is there any other library which adds posix functionalities like popen to Fortran? Or any other way which does not depend on external, non default libraries? @francescalus
– Yuki.kuroshita
Nov 23 '18 at 15:20
Some compilers bundle POSIX-like things in their runtime, so you may have luck there. But, to be honest, I'd just write standard output of the command to a real file and read it from my Fortran program.
– francescalus
Nov 23 '18 at 15:22
Some compilers bundle POSIX-like things in their runtime, so you may have luck there. But, to be honest, I'd just write standard output of the command to a real file and read it from my Fortran program.
– francescalus
Nov 23 '18 at 15:22
Thing is, this will go into a program for differential evolution with millions of generations, with 40 models, each with 4 model parameters, looped over 120 data points, so total iterations would be 19200000000 at max. I don't know if writing to a file and then reading from it each time would be the best thing to do here. The whole point of writing a differential evolution algorithm is to make things faster. I would have preferred to not have to read and write a file in each iteration
– Yuki.kuroshita
Nov 23 '18 at 15:33
Thing is, this will go into a program for differential evolution with millions of generations, with 40 models, each with 4 model parameters, looped over 120 data points, so total iterations would be 19200000000 at max. I don't know if writing to a file and then reading from it each time would be the best thing to do here. The whole point of writing a differential evolution algorithm is to make things faster. I would have preferred to not have to read and write a file in each iteration
– Yuki.kuroshita
Nov 23 '18 at 15:33
2
2
This article about named pipes is interesting networkworld.com/article/3251853/linux/… (which says that everything is performed on memory. But I wonder whether a huge number of system calls background is no problem or have some practical issue...)
– roygvib
Nov 23 '18 at 19:47
This article about named pipes is interesting networkworld.com/article/3251853/linux/… (which says that everything is performed on memory. But I wonder whether a huge number of system calls background is no problem or have some practical issue...)
– roygvib
Nov 23 '18 at 19:47
|
show 2 more comments
1 Answer
1
active
oldest
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4
Since you're using BASH, lets assume you're working on some kind of unix-like system. So you could use a FIFO. Something like
program readfifo
implicit none
integer :: u, i
logical :: ex
inquire(exist=ex, file='foo')
if (.not. ex) then
call execute_command_line ("mkfifo foo")
end if
call execute_command_line ("echo 5 > foo&")
open(newunit=u, file='foo', action='read')
read(u, *) i
write(*, *) 'Managed to read the value ', i
end program readfifoNote that the semantics of FIFO's wrt blocking can be a bit tricky (that's why there is the '&' after the echo command, you might want to read up on it a bit and experiment (particularly make sure you haven't got a zillion bash processes hanging around when you do this multiple times).
answered Nov 23 '18 at 16:32
janneb
27.8k25777
So, is using named pipes faster than using normal files? Like in the above code, if I don't use the commandmkfifo foo, and just write it to a normal file, and then read from it, would it be comparably slower? Because as far as I understood, even making a named pipe will have to write a file to the disk
– Yuki.kuroshita
Nov 23 '18 at 17:20
1
@Yuki.kuroshita: Well, you have to create the FIFO entry in the directory yes, but then all I/O to/from that FIFO never hits the filesystem. So if you create the FIFO only once, and then keep it open in Fortran, I guess it would be pretty efficient. Well, roughly as efficient as a pipe, since that's what it is.
– janneb
Nov 23 '18 at 18:15
Thank you for the explanation
– Yuki.kuroshita
Nov 23 '18 at 19:28
add a comment |
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4
Since you're using BASH, lets assume you're working on some kind of unix-like system. So you could use a FIFO. Something like
program readfifo
implicit none
integer :: u, i
logical :: ex
inquire(exist=ex, file='foo')
if (.not. ex) then
call execute_command_line ("mkfifo foo")
end if
call execute_command_line ("echo 5 > foo&")
open(newunit=u, file='foo', action='read')
read(u, *) i
write(*, *) 'Managed to read the value ', i
end program readfifoNote that the semantics of FIFO's wrt blocking can be a bit tricky (that's why there is the '&' after the echo command, you might want to read up on it a bit and experiment (particularly make sure you haven't got a zillion bash processes hanging around when you do this multiple times).
answered Nov 23 '18 at 16:32
janneb
27.8k25777
So, is using named pipes faster than using normal files? Like in the above code, if I don't use the commandmkfifo foo, and just write it to a normal file, and then read from it, would it be comparably slower? Because as far as I understood, even making a named pipe will have to write a file to the disk
– Yuki.kuroshita
Nov 23 '18 at 17:20
1
@Yuki.kuroshita: Well, you have to create the FIFO entry in the directory yes, but then all I/O to/from that FIFO never hits the filesystem. So if you create the FIFO only once, and then keep it open in Fortran, I guess it would be pretty efficient. Well, roughly as efficient as a pipe, since that's what it is.
– janneb
Nov 23 '18 at 18:15
Thank you for the explanation
– Yuki.kuroshita
Nov 23 '18 at 19:28
add a comment |
4
Since you're using BASH, lets assume you're working on some kind of unix-like system. So you could use a FIFO. Something like
program readfifo
implicit none
integer :: u, i
logical :: ex
inquire(exist=ex, file='foo')
if (.not. ex) then
call execute_command_line ("mkfifo foo")
end if
call execute_command_line ("echo 5 > foo&")
open(newunit=u, file='foo', action='read')
read(u, *) i
write(*, *) 'Managed to read the value ', i
end program readfifoNote that the semantics of FIFO's wrt blocking can be a bit tricky (that's why there is the '&' after the echo command, you might want to read up on it a bit and experiment (particularly make sure you haven't got a zillion bash processes hanging around when you do this multiple times).
answered Nov 23 '18 at 16:32
janneb
27.8k25777
So, is using named pipes faster than using normal files? Like in the above code, if I don't use the commandmkfifo foo, and just write it to a normal file, and then read from it, would it be comparably slower? Because as far as I understood, even making a named pipe will have to write a file to the disk
– Yuki.kuroshita
Nov 23 '18 at 17:20
1
@Yuki.kuroshita: Well, you have to create the FIFO entry in the directory yes, but then all I/O to/from that FIFO never hits the filesystem. So if you create the FIFO only once, and then keep it open in Fortran, I guess it would be pretty efficient. Well, roughly as efficient as a pipe, since that's what it is.
– janneb
Nov 23 '18 at 18:15
Thank you for the explanation
– Yuki.kuroshita
Nov 23 '18 at 19:28
add a comment |
4
4
4
Since you're using BASH, lets assume you're working on some kind of unix-like system. So you could use a FIFO. Something like
program readfifo
implicit none
integer :: u, i
logical :: ex
inquire(exist=ex, file='foo')
if (.not. ex) then
call execute_command_line ("mkfifo foo")
end if
call execute_command_line ("echo 5 > foo&")
open(newunit=u, file='foo', action='read')
read(u, *) i
write(*, *) 'Managed to read the value ', i
end program readfifoNote that the semantics of FIFO's wrt blocking can be a bit tricky (that's why there is the '&' after the echo command, you might want to read up on it a bit and experiment (particularly make sure you haven't got a zillion bash processes hanging around when you do this multiple times).
answered Nov 23 '18 at 16:32
janneb
27.8k25777
Since you're using BASH, lets assume you're working on some kind of unix-like system. So you could use a FIFO. Something like
program readfifo
implicit none
integer :: u, i
logical :: ex
inquire(exist=ex, file='foo')
if (.not. ex) then
call execute_command_line ("mkfifo foo")
end if
call execute_command_line ("echo 5 > foo&")
open(newunit=u, file='foo', action='read')
read(u, *) i
write(*, *) 'Managed to read the value ', i
end program readfifoNote that the semantics of FIFO's wrt blocking can be a bit tricky (that's why there is the '&' after the echo command, you might want to read up on it a bit and experiment (particularly make sure you haven't got a zillion bash processes hanging around when you do this multiple times).
answered Nov 23 '18 at 16:32
janneb
27.8k25777
answered Nov 23 '18 at 16:32
janneb
27.8k25777
answered Nov 23 '18 at 16:32
janneb
27.8k25777
answered Nov 23 '18 at 16:32
janneb
27.8k25777
27.8k25777
So, is using named pipes faster than using normal files? Like in the above code, if I don't use the commandmkfifo foo, and just write it to a normal file, and then read from it, would it be comparably slower? Because as far as I understood, even making a named pipe will have to write a file to the disk
– Yuki.kuroshita
Nov 23 '18 at 17:20
1
@Yuki.kuroshita: Well, you have to create the FIFO entry in the directory yes, but then all I/O to/from that FIFO never hits the filesystem. So if you create the FIFO only once, and then keep it open in Fortran, I guess it would be pretty efficient. Well, roughly as efficient as a pipe, since that's what it is.
– janneb
Nov 23 '18 at 18:15
Thank you for the explanation
– Yuki.kuroshita
Nov 23 '18 at 19:28
add a comment |
So, is using named pipes faster than using normal files? Like in the above code, if I don't use the commandmkfifo foo, and just write it to a normal file, and then read from it, would it be comparably slower? Because as far as I understood, even making a named pipe will have to write a file to the disk
– Yuki.kuroshita
Nov 23 '18 at 17:20
1
@Yuki.kuroshita: Well, you have to create the FIFO entry in the directory yes, but then all I/O to/from that FIFO never hits the filesystem. So if you create the FIFO only once, and then keep it open in Fortran, I guess it would be pretty efficient. Well, roughly as efficient as a pipe, since that's what it is.
– janneb
Nov 23 '18 at 18:15
Thank you for the explanation
– Yuki.kuroshita
Nov 23 '18 at 19:28
So, is using named pipes faster than using normal files? Like in the above code, if I don't use the command
mkfifo foo, and just write it to a normal file, and then read from it, would it be comparably slower? Because as far as I understood, even making a named pipe will have to write a file to the disk– Yuki.kuroshita
Nov 23 '18 at 17:20
So, is using named pipes faster than using normal files? Like in the above code, if I don't use the command
mkfifo foo, and just write it to a normal file, and then read from it, would it be comparably slower? Because as far as I understood, even making a named pipe will have to write a file to the disk– Yuki.kuroshita
Nov 23 '18 at 17:20
1
1
@Yuki.kuroshita: Well, you have to create the FIFO entry in the directory yes, but then all I/O to/from that FIFO never hits the filesystem. So if you create the FIFO only once, and then keep it open in Fortran, I guess it would be pretty efficient. Well, roughly as efficient as a pipe, since that's what it is.
– janneb
Nov 23 '18 at 18:15
@Yuki.kuroshita: Well, you have to create the FIFO entry in the directory yes, but then all I/O to/from that FIFO never hits the filesystem. So if you create the FIFO only once, and then keep it open in Fortran, I guess it would be pretty efficient. Well, roughly as efficient as a pipe, since that's what it is.
– janneb
Nov 23 '18 at 18:15
Thank you for the explanation
– Yuki.kuroshita
Nov 23 '18 at 19:28
Thank you for the explanation
– Yuki.kuroshita
Nov 23 '18 at 19:28
add a comment |
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1
You'll have to use a temporary "file". I can't immediately find a question which I thought covered this, but some discussion is in this one.
– francescalus
Nov 23 '18 at 13:53
I have been trying and failing to make the fortranposix library mentioned in the question (an fPIC error for an object file which is not there in the Makefile). While I am figuring it out, is there any other library which adds posix functionalities like popen to Fortran? Or any other way which does not depend on external, non default libraries? @francescalus
– Yuki.kuroshita
Nov 23 '18 at 15:20
Some compilers bundle POSIX-like things in their runtime, so you may have luck there. But, to be honest, I'd just write standard output of the command to a real file and read it from my Fortran program.
– francescalus
Nov 23 '18 at 15:22
Thing is, this will go into a program for differential evolution with millions of generations, with 40 models, each with 4 model parameters, looped over 120 data points, so total iterations would be 19200000000 at max. I don't know if writing to a file and then reading from it each time would be the best thing to do here. The whole point of writing a differential evolution algorithm is to make things faster. I would have preferred to not have to read and write a file in each iteration
– Yuki.kuroshita
Nov 23 '18 at 15:33
2
This article about named pipes is interesting networkworld.com/article/3251853/linux/… (which says that everything is performed on memory. But I wonder whether a huge number of system calls background is no problem or have some practical issue...)
– roygvib
Nov 23 '18 at 19:47