The stdlib_system module provides interface for interacting with external processes, enabling the execution
and monitoring of system commands or applications directly from Fortran.
run - Execute an external process synchronouslyExperimental
The run interface allows execution of external processes using a single command string or a list of arguments.
Processes run synchronously, meaning execution is blocked until the process finishes.
Optional arguments enable the collection of standard output and error streams, as well as sending input via standard input.
Additionally, a callback function can be specified to execute upon process completion, optionally receiving a user-defined payload.
process = stdlib_subprocess (args [, stdin] [, want_stdout] [, want_stderr] [, callback] [, payload])
args: Shall be a character(*) string (for command-line execution) or a character(*), dimension(:) array (for argument-based execution). It specifies the command and arguments to execute. This is an intent(in) argument.
stdin (optional): Shall be a character(*) value containing input to send to the process via standard input (pipe). This is an intent(in) argument.
want_stdout (optional): Shall be a logical flag. If .true., the standard output of the process will be captured; if .false. (default), it will be lost. This is an intent(in) argument.
want_stderr (optional): Shall be a logical flag. If .true., the standard error output of the process will be captured. If .false. (default), it will be lost. This is an intent(in) argument.
callback (optional): Shall be a procedure conforming to the process_callback interface. If present, this function will be called upon process completion with the process ID, exit state, and optionally collected standard input, output, and error streams. This is an intent(in) argument.
payload (optional): Shall be a generic (class(*)) scalar that will be passed to the callback function upon process completion. It allows users to associate custom data with the process execution. This is an intent(inout), target argument.
Returns an object of type process_type that contains information about the state of the created process.
! Example usage with command line or list of arguments
type(process_type) :: p
! Run a simple command line synchronously
p = run("echo 'Hello, world!'", want_stdout=.true.)
runasync - Execute an external process asynchronouslyExperimental
The runasync interface allows execution of external processes using a single command string or a list of arguments.
Processes are run asynchronously (non-blocking), meaning execution does not wait for the process to finish.
Optional arguments enable the collection of standard output and error streams, as well as sending input via standard input.
Additionally, a callback function can be specified to execute upon process completion, optionally receiving a user-defined payload.
process = stdlib_subprocess (args [, stdin] [, want_stdout] [, want_stderr] [, callback] [, payload])
args: Shall be a character(*) string (for command-line execution) or a character(*), dimension(:) array (for argument-based execution). It specifies the command and arguments to execute. This is an intent(in) argument.
stdin (optional): Shall be a character(*) value containing input to send to the process via standard input (pipe). This is an intent(in) argument.
want_stdout (optional): Shall be a logical flag. If .true., the standard output of the process will be captured; if .false. (default), it will be lost. This is an intent(in) argument.
want_stderr (optional): Shall be a logical flag. If .true., the standard error output of the process will be captured. Default: .false.. This is an intent(in) argument.
callback (optional): Shall be a procedure conforming to the process_callback interface. If present, this function will be called upon process completion with the process ID, exit state, and optionally collected standard input, output, and error streams. This is an intent(in) argument.
payload (optional): Shall be a generic (class(*)) scalar that will be passed to the callback function upon process completion. It allows users to associate custom data with the process execution. This is an intent(inout), target argument.
Returns an object of type process_type that contains information about the state of the created process.
! Process example 1: Run a Command Synchronously and Capture Output
program run_sync
use stdlib_system, only: run, is_completed, is_windows, process_type
implicit none
type(process_type) :: p
logical :: completed
! Run a synchronous process to list directory contents
if (is_windows()) then
p = run("dir", want_stdout=.true.)
else
p = run("ls -l", want_stdout=.true.)
end if
! Check if the process is completed (should be true since wait=.true.)
if (is_completed(p)) then
print *, "Process completed successfully. The current directory: "
print *, p%stdout
else
print *, "Process is still running (unexpected)."
end if
end program run_sync
is_running - Check if a process is still runningExperimental
The is_running interface provides a method to check if an external process is still running.
This is useful for monitoring the status of asynchronous processes created with the run interface.
status = stdlib_subprocess (process)
process: Shall be a type(process_type) object representing the external process to check. This is an intent(inout) argument.
Returns a logical value: .true. if the process is still running, or .false. if the process has terminated.
After a call to is_running, the type(process_type) structure is also updated to the latest process state.
! Process example 2: Run an Asynchronous Command and check its status
program run_async
use stdlib_system, only: process_type, runasync, is_running, wait
implicit none
type(process_type) :: p
! Run an asynchronous process to sleep for 1 second
p = runasync("sleep 1")
! Check if the process is running
if (is_running(p)) then
print *, "Process is running."
else
print *, "Process has already completed."
end if
! Wait for the process to complete
call wait(p, max_wait_time = 5.0)
print *, "Process has now completed."
end program run_async
is_completed - Check if a process has completed executionExperimental
The is_completed interface provides a method to check if an external process has finished execution.
This is useful for determining whether asynchronous processes created with the run interface have terminated.
status = stdlib_subprocess (process)
process: Shall be a type(process_type) object representing the external process to check. This is an intent(inout) argument.
Returns a logical value:
- .true. if the process has completed.
- .false. if the process is still running.
After a call to is_completed, the type(process_type) structure is updated to reflect the latest process state.
! Process example 1: Run a Command Synchronously and Capture Output
program run_sync
use stdlib_system, only: run, is_completed, is_windows, process_type
implicit none
type(process_type) :: p
logical :: completed
! Run a synchronous process to list directory contents
if (is_windows()) then
p = run("dir", want_stdout=.true.)
else
p = run("ls -l", want_stdout=.true.)
end if
! Check if the process is completed (should be true since wait=.true.)
if (is_completed(p)) then
print *, "Process completed successfully. The current directory: "
print *, p%stdout
else
print *, "Process is still running (unexpected)."
end if
end program run_sync
elapsed - Return process lifetime in secondsExperimental
The elapsed interface provides a method to calculate the total time that has elapsed since a process was started.
This is useful for tracking the duration of an external process or for performance monitoring purposes.
The result is a real value representing the elapsed time in seconds, measured from the time the process was created.
delta_t = stdlib_subprocess (process)
process: Shall be a type(process_type) object representing the external process. It is an intent(in) argument.
Returns a real(real64) value that represents the elapsed time (in seconds) since the process was started.
If the process is still running, the value returned is the time elapsed until the call to this function.
Otherwise, the total process duration from creation until completion is returned.
! Process example 3: Run with many arguments, and check runtime
program run_with_args
use stdlib_system, only: process_type, run, elapsed, wait
implicit none
type(process_type) :: p
character(len=15), allocatable :: args(:)
! Define arguments for the `echo` command
allocate(args(2))
args(1) = "echo"
args(2) = "Hello, Fortran!"
! Run the command with arguments (synchronous)
p = run(args)
! Print the runtime of the process
print *, "Process runtime:", elapsed(p), "seconds."
! Clean up
deallocate(args)
end program run_with_args
wait - Wait until a running process is completedExperimental
The wait interface provides a method to block the calling program until the specified process completes.
If the process is running asynchronously, this subroutine will pause the workflow until the given process finishes.
Additionally, an optional maximum wait time can be provided. If the process does not finish within the specified time,
the subroutine will return without waiting further.
On return from this routine, the process state is accordingly updated. This is useful when you want to wait for a background task to complete, but want to avoid indefinite blocking in case of process hang or delay.
call stdlib_subprocess (process [, max_wait_time])
process: Shall be a type(process_type) object representing the external process to monitor.
This is an intent(inout) argument, and its state is updated upon completion.
max_wait_time (optional): Shall be a real value specifying the maximum wait time in seconds.
If not provided, the subroutine will wait indefinitely until the process completes.
! Process example 2: Run an Asynchronous Command and check its status
program run_async
use stdlib_system, only: process_type, runasync, is_running, wait
implicit none
type(process_type) :: p
! Run an asynchronous process to sleep for 1 second
p = runasync("sleep 1")
! Check if the process is running
if (is_running(p)) then
print *, "Process is running."
else
print *, "Process has already completed."
end if
! Wait for the process to complete
call wait(p, max_wait_time = 5.0)
print *, "Process has now completed."
end program run_async
update - Update the internal state of a processExperimental
The update interface allows the internal state of a process object to be updated by querying the system.
After the process completes, the standard output and standard error are retrieved, if they were requested, and loaded into the process%stdout and process%stderr string variables, respectively.
This is especially useful for monitoring asynchronous processes and retrieving their output after they have finished.
call stdlib_subprocess (process)
process: Shall be a type(process_type) object representing the external process whose state needs to be updated.
This is an intent(inout) argument, and its internal state is updated on completion.
! Process example 5: Object-oriented interface
program example_process_5
use stdlib_system, only: process_type, runasync, is_windows, sleep, update
implicit none
type(process_type) :: process
if (is_windows()) then
process = runasync("ping -n 10 127.0.0.1")
else
process = runasync("ping -c 10 127.0.0.1")
endif
! Verify the process is running
do while (process%is_running())
! Update process state
call update(process)
! Wait a bit before killing the process
call sleep(millisec=1500)
print *, "Process has been running for ",process%elapsed()," seconds..."
end do
print *, "Process ",process%pid()," completed in ",process%elapsed()," seconds."
end program example_process_5
kill - Terminate a running processExperimental
The kill interface is used to terminate a running external process. It attempts to stop the process and returns a boolean flag indicating whether the operation was successful.
This interface is useful when a process needs to be forcefully stopped, for example, if it becomes unresponsive or if its execution is no longer required.
call stdlib_subprocess (process, success)
process: Shall be a type(process_type) object representing the external process to be terminated.
This is an intent(inout) argument, and on return is updated with the terminated process state.
success: Shall be a logical variable. It is set to .true. if the process was successfully killed, or .false. otherwise.
! Process example 4: Kill a running process
program example_process_kill
use stdlib_system, only: process_type, runasync, is_running, kill, elapsed, is_windows, sleep
implicit none
type(process_type) :: process
logical :: running, success
print *, "Starting a long-running process..."
if (is_windows()) then
process = runasync("ping -n 10 127.0.0.1")
else
process = runasync("ping -c 10 127.0.0.1")
endif
! Verify the process is running
running = is_running(process)
print *, "Process running:", running
! Wait a bit before killing the process
call sleep(millisec=250)
print *, "Killing the process..."
call kill(process, success)
if (success) then
print *, "Process killed successfully."
else
print *, "Failed to kill the process."
endif
! Verify the process is no longer running
running = is_running(process)
print *, "Process running after kill:", running
end program example_process_kill
sleep - Pause execution for a specified time in millisecondsExperimental
The sleep interface pauses the execution of a program for a specified duration, given in milliseconds.
This routine acts as a cross-platform wrapper, abstracting the underlying platform-specific sleep implementations.
It ensures that the requested sleep duration is honored on both Windows and Unix-like systems.
call stdlib_system (millisec)
millisec: Shall be an integer representing the number of milliseconds to sleep. This is an intent(in) argument.
! Usage of `sleep`
program example_sleep
use stdlib_system, only: sleep
implicit none
print *, "Starting sleep..."
! Sleep for 500 milliseconds
call sleep(500)
print *, "Finished sleeping!"
end program example_sleep
is_windows - Check if the system is running on WindowsExperimental
The is_windows interface provides a quick, compile-time check to determine if the current system is Windows.
It leverages a C function that checks for the presence of the _WIN32 macro, which is defined in C compilers when targeting Windows.
This function is highly efficient and works during the compilation phase, avoiding the need for runtime checks.
result = stdlib_system ()
Returns a logical flag: .true. if the system is Windows, or .false. otherwise.
! Process example 1: Run a Command Synchronously and Capture Output
program run_sync
use stdlib_system, only: run, is_completed, is_windows, process_type
implicit none
type(process_type) :: p
logical :: completed
! Run a synchronous process to list directory contents
if (is_windows()) then
p = run("dir", want_stdout=.true.)
else
p = run("ls -l", want_stdout=.true.)
end if
! Check if the process is completed (should be true since wait=.true.)
if (is_completed(p)) then
print *, "Process completed successfully. The current directory: "
print *, p%stdout
else
print *, "Process is still running (unexpected)."
end if
end program run_sync