Is there a way within fortran to direct unit 0 (error output) to a file? Particularly I want to redirect it to standard out. I am hoping for something within Fortran that would be portable across major operating systems. I did try
open(unit=0,file="stuff")
and
open(unit=0,file='/dev/tty')
with gfortran under Linux, but the open statement seemed to have no effect.

Daniel Feenberg
NBER

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Daniel Feenberg wrote:

Is there a way within fortran to direct unit 0 (error output) to a file? Particularly I want to redirect it to standard out. I am hoping for something within Fortran that would be portable across major operating systems. I did try
open(unit=0,file="stuff")
and
open(unit=0,file='/dev/tty')
with gfortran under Linux, but the open statement seemed to have no effect.

Daniel Feenberg
NBER

You can try to close ERROR_UNIT from ISO_FORTRAN_ENV
and then re-use that unit number. Not sure if it works.

program foo
use iso_fortran_env
close(ERROR_UNIT)
open(unit=ERROR_UNIT,file=....)
end program foo

--
steve

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On Wednesday, September 8, 2021 at 4:07:05 PM UTC-4, steve kargl wrote:

Daniel Feenberg wrote:

Is there a way within fortran to direct unit 0 (error output) to a file? Particularly I want to redirect it to standard out. I am hoping for something within Fortran that would be portable across major operating systems. I did try

...

You can try to close ERROR_UNIT from ISO_FORTRAN_ENV
and then re-use that unit number. Not sure if it works.

program foo
use iso_fortran_env
close(ERROR_UNIT)
open(unit=ERROR_UNIT,file=....)
end program foo

--
steve

Just tried it out in gfortran Linux and FreeBSD - no effect on the destination of error output. I did want to avoid depending on the shell for this because different shells have different syntax for this, and I don't want to explain that to users or tell
them which shell to use.
Daniel Feenberg

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Daniel Feenberg wrote:

On Wednesday, September 8, 2021 at 4:07:05 PM UTC-4, steve kargl wrote:

Daniel Feenberg wrote:

Is there a way within fortran to direct unit 0 (error output) to a file? Particularly I want to redirect it to standard out. I am hoping for something within Fortran that would be portable across major operating systems. I did try

...

You can try to close ERROR_UNIT from ISO_FORTRAN_ENV
and then re-use that unit number. Not sure if it works.

program foo
use iso_fortran_env
close(ERROR_UNIT)
open(unit=ERROR_UNIT,file=....)
end program foo

--
steve

Just tried it out in gfortran Linux and FreeBSD - no effect on the destination of error output. I did want to avoid depending on the shell for this because different shells have different syntax for this, and I don't want to explain that to users or

tell them which shell to use.

Daniel Feenberg

Gfortran has an environmental variable that allows one to change the unit
to some other value, but suspect that doesn't change the internal use of
stderr (as found in C). Even if an EV worked, you would to users how to
an EV for the different shells.

--
steve

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On 9/8/2021 2:57 PM, Daniel Feenberg wrote:

Is there a way within fortran to direct unit 0 (error output) to a file?

There are two different things at work here. Unit 0 (or whatever
ERROR_UNIT is defined as) is often "preconnected" to stderr. You are
free to reopen that unit on a file, but it is no longer "error output".
Any output that would normally go to stderr, other than explicit writes
to unit 0, will still go to stderr.

The only way I know of to do the redirection you seek is to do it on the command line invoking the program.

--
Steve Lionel
ISO/IEC JTC1/SC22/WG5 (Fortran) Convenor
Retired Intel Fortran developer/support
Email: firstname at firstnamelastname dot com
Twitter: @DoctorFortran
LinkedIn: https://www.linkedin.com/in/stevelionel
Blog: https://stevelionel.com/drfortran
WG5: https://wg5-fortran.org

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On Wednesday, September 8, 2021 at 4:11:50 PM UTC-7, steve kargl wrote:

(snip)

Gfortran has an environmental variable that allows one to change the unit
to some other value, but suspect that doesn't change the internal use of stderr (as found in C). Even if an EV worked, you would to users how to
an EV for the different shells.

You can change an EV within the program. Exactly when its value is needed, isn't so obvious. It might be not read until an actual I/O operations is needed.

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On 9/8/2021 8:36 PM, gah4 wrote:

On Wednesday, September 8, 2021 at 4:11:50 PM UTC-7, steve kargl wrote:

(snip)

Gfortran has an environmental variable that allows one to change the unit
to some other value, but suspect that doesn't change the internal use of
stderr (as found in C). Even if an EV worked, you would to users how to
an EV for the different shells.

You can change an EV within the program. Exactly when its value is needed, isn't so obvious. It might be not read until an actual I/O operations is needed.

Depends on the operating system.

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On Thursday, September 9, 2021 at 3:01:00 AM UTC-7, Gary Scott wrote:

(snip, I wrote)

You can change an EV within the program. Exactly when its value is needed, isn't so obvious. It might be not read until an actual I/O operations is needed.

Depends on the operating system.

OK, back to the start.

As it says above: "I did want to avoid depending on the shell for this because
different shells have different syntax for this, and I don't want to explain
that to users or tell them which shell to use."

That happens if one asks the user to add variables to the system.

But the other way is to supply a shell script that the user runs, which then runs
the actual program. Unix-like systems run such in a Bourne (sh) shell, unless told
otherwise, independent of the user's actual shell. It does that just for the reason
given: that it works independent of the user's actual shell.

(Except that csh and descendants, if it starts with # and not #!, will run it in a shell like itself.)

The other other way is to start with #! and the path of a program (shell)
to use to run it.

Of course DOS/Windows use a different system, but the executable file has
to be different, too.

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