Operating system interface

6.27

Operating system interface

6.27.1 argument_counter/1

Templates

: argument_counter(?integer)

Description

argument_counter(Counter) succeeds if Counter is the number of arguments of the command-line. Since the first argument is always the name of the running program, Counter is always ³ 1.

Errors

Counter is neither a variable nor an integer type_error(integer, Counter)

Portability

GNU Prolog predicate.

6.27.2 argument_value/2

Templates

: argument_value(+integer, ?atom)

Description

argument_value(N, Arg) succeeds if the Nth argument on the command-line unifies with Arg. The first argument is always the name of the running program and its number is 0. The number of arguments on the command-line can be obtained using argument_counter/1 (section 6.27.1).

Errors

N is a variable instantiation_error

N is neither a variable nor an integer type_error(integer, N)

N is an integer < 0 domain_error(not_less_than_zero, N)

Arg is neither a variable nor an atom type_error(atom, Arg)

Portability

GNU Prolog predicate.

6.27.3 argument_list/1

Templates

: argument_list(?list)

Description

argument_list(Args) succeeds if Args unifies with the list of atoms associated to each argument on the command-line other than the first argument (the name of the running program).

Errors

Args is neither a partial list nor a list type_error(list, Args)

Portability

GNU Prolog predicate.

6.27.4 environ/2

Templates

: environ(?atom, ?atom)

Description

environ(Name, Value) succeeds if Name is the name of an environment variable whose value is Value. This predicate is re-executable on backtracking.

Errors

Name is neither a variable nor an atom type_error(atom, Name)

Value is neither a variable nor an atom type_error(atom, Value)

Portability

GNU Prolog predicate.

6.27.5 make_directory/1, delete_directory/1, change_directory/1

Templates

: make_directory(+atom) delete_directory(+atom) change_directory(+atom)

Description

make_directory(PathName) creates the directory whose pathname is PathName.

delete_directory(PathName) removes the directory whose pathname is PathName.

change_directory(PathName) sets the current directory to the directory whose pathname is PathName.

See absolute_file_name/2 for information about the syntax of PathName (section 6.26.1).

Errors

PathName is a variable instantiation_error

PathName is neither a variable nor an atom type_error(atom, PathName)

PathName is an atom but not a valid pathname domain_error(os_path, PathName)

an operating system error occurs and the value of the os_error Prolog flag is error (section 6.22.1) system_error(atom explaining the error)

Portability

GNU Prolog predicates.

6.27.6 working_directory/1

Templates

: working_directory(?atom)

Description

working_directory(PathName) succeeds if PathName is the pathname of the current directory.

Errors

PathName is neither a variable nor an atom type_error(atom, PathName)

Portability

GNU Prolog predicate.

6.27.7 directory_files/2

Templates

: directory_files(+atom, ?list)

Description

directory_files(PathName, Files) succeeds if Files is the list of all entries (files, sub-directories,...) in the directory whose pathname is PathName. See absolute_file_name/2 for information about the syntax of PathName (section 6.26.1).

Errors

PathName is a variable instantiation_error

PathName is neither a variable nor an atom type_error(atom, PathName)

PathName is an atom but not a valid pathname domain_error(os_path, PathName)

Files is neither a partial list nor a list type_error(list, Files)

an operating system error occurs and the value of the os_error Prolog flag is error (section 6.22.1) system_error(atom explaining the error)

Portability

GNU Prolog predicate.

6.27.8 rename_file/2

Templates

: rename_file(+atom, +atom)

Description

rename_file(PathName1, PathName2) renames the file or directory whose pathname is PathName1 to PathName2. See absolute_file_name/2 for information about the syntax of PathName1 and PathName2 (section 6.26.1).

Errors

PathName1 is a variable instantiation_error

PathName1 is neither a variable nor an atom type_error(atom, PathName1)

PathName1 is an atom but not a valid pathname domain_error(os_path, PathName1)

PathName2 is a variable instantiation_error

PathName2 is neither a variable nor an atom type_error(atom, PathName2)

PathName2 is an atom but not a valid pathname domain_error(os_path, PathName2)

an operating system error occurs and value of the os_error Prolog flag is error (section 6.22.1) system_error(atom explaining the error)

Portability

GNU Prolog predicate.

6.27.9 delete_file/1, unlink/1

Templates

: delete_file(PathName) unlink(PathName)

Description

delete_file(PathName) removes the existing file whose pathname is PathName.

unlink/1 is similar to delete_file/1 except that it never causes a system_error (e.g. if PathName does not refer to an existing file).

See absolute_file_name/2 for information about the syntax of PathName (section 6.26.1).

Errors

PathName is a variable instantiation_error

PathName is neither a variable nor an atom type_error(atom, PathName)

PathName is an atom but not a valid pathname domain_error(os_path, PathName)

an operating system error occurs and the value of the os_error Prolog flag is error (section 6.22.1) system_error(atom explaining the error)

Portability

GNU Prolog predicates.

6.27.10 file_permission/2, file_exists/1

Templates

: file_permission(+atom, +atom) file_permission(+atom, +atom_list) file_exists(+atom)

Description

file_permission(PathName, Permission) succeeds if PathName is the pathname of an existing file (or directory) whose permissions include Permission.

File permissions: Permission can be a single permission or a list of permissions. A permission is an atom among:

read: the file or directory can be read.
write: the file or directory can be written.
execute: the file can be executed.
search: the directory can be searched.

If PathName does not exists or if it its permissions do not include Permission this predicate fails.

file_exists(PathName) is equivalent to file_permission(PathName, []), i.e. it succeeds if PathName is the pathname of an existing file (or directory).

See absolute_file_name/2 for information about the syntax of PathName (section 6.26.1).

Errors

PathName is a variable instantiation_error

PathName is neither a variable nor an atom type_error(atom, PathName)

PathName is an atom but not a valid pathname domain_error(os_path, PathName)

Permission is a partial list or a list with an element which is a variable instantiation_error

Permission is neither an atom nor partial list or a list type_error(list, Permission)

an element E of the Permission list is neither a variable nor an atom type_error(atom, E)

an element E of the Permission is an atom but not a valid permission domain_error(os_file_permission, Permission)

an operating system error occurs and the value of the os_error Prolog flag is error (section 6.22.1) system_error(atom explaining the error)

Portability

GNU Prolog predicates.

6.27.11 file_property/2

Templates

: file_property(+atom, ?os_file_property)

Description

file_property(PathName, Property) succeeds if PathName is the pathname of an existing file (or directory) and if Property unifies with one of the properties of the file. This predicate is re-executable on backtracking.

File properties:

absolute_file_name(File): File is the absolute file name of PathName (section 6.26.1).
real_file_name(File): File is the real file name of PathName (follows symbolic links).
type(Type): Type is the type of PathName. Possible values are: regular, directory, fifo, socket, character_device, block_device or unknown.
size(Size): Size is the size (in bytes) of PathName.
permission(Permission): Permission is a permission of PathName (section 6.27.10).
last_modification(DT): DT is the last modification date and time (section 6.27.14).

See absolute_file_name/2 for information about the syntax of PathName (section 6.26.1).

Errors

PathName is a variable instantiation_error

PathName is neither a variable nor an atom type_error(atom, PathName)

PathName is an atom but not a valid pathname domain_error(os_path, PathName)

Property is neither a variable nor a file property term domain_error(os_file_property, Property)

Property = absolute_file_name(E), real_file_name(E), type(E) or permission(E) and E is neither a variable nor an atom type_error(atom, E)

Property = last_modification(DateTime) and DateTime is neither a variable nor a compound term type_error(compound, DateTime)

Property = last_modification(DateTime) and DateTime is a compound term but not a structure dt/6 domain_error(date_time, DateTime)

Property = size(E) or last_modification(DateTime) and DateTime is a structure dt/6 but an element E is neither a variable nor an integer type_error(integer, E)

an operating system error occurs and the value of the os_error Prolog flag is error (section 6.22.1) system_error(atom explaining the error)

Portability

GNU Prolog predicate.

6.27.12 temporary_name/2

Templates

: temporary_name(+atom, ?atom)

Description

temporary_name(Template, PathName) creates a unique file name PathName whose pathname begins by Template. Template should contain a pathname with six trailing Xs. PathName is Template with the six Xs replaced with a letter and the process identifier. This predicate is an interface to the C Unix function mktemp(3).

See absolute_file_name/2 for information about the syntax of Template (section 6.26.1).

Errors

Template is a variable instantiation_error

Template is neither a variable nor an atom type_error(atom, Template)

Template is an atom but not a valid pathname domain_error(os_path, Template)

PathName is neither a variable nor an atom type_error(atom, PathName)

an operating system error occurs and the value of the os_error Prolog flag is error (section 6.22.1) system_error(atom explaining the error)

Portability

GNU Prolog predicate.

6.27.13 temporary_file/3

Templates

: temporary_file(+atom, +atom, ?atom)

Description

temporary_file(Directory, Prefix, PathName) creates a unique file name PathName whose pathname begins by Directory/Prefix. If Directory is the empty atom '' a standard temporary directory will be used (e.g. /tmp). Prefix can be the empty atom ''. This predicate is an interface to the C Unix function tempnam(3).

See absolute_file_name/2 for information about the syntax of Directory (section 6.26.1).

Errors

Directory is a variable instantiation_error

Directory is neither a variable nor an atom type_error(atom, Directory)

Directory is an atom but not a valid pathname domain_error(os_path, Directory)

Prefix is a variable instantiation_error

Prefix is neither a variable nor an atom type_error(atom, Prefix)

PathName is neither a variable nor an atom type_error(atom, PathName)

an operating system error occurs and the value of the os_error Prolog flag is error (section 6.22.1) system_error(atom explaining the error)

Portability

GNU Prolog predicate.

6.27.14 date_time/1

Templates

: date_time(?compound)

Description

date_time(DateTime) unifies DateTime with a compound term containing the current date and time. DateTime is a structure dt(Year, Month, Day, Hour, Minute, Second). Each sub-argument of the term dt/6 is an integer.

Errors

DateTime is neither a variable nor a compound term type_error(compound, DateTime)

DateTime is a compound term but not a structure dt/6 domain_error(date_time, DateTime)

DateTime is a structure dt/6 and an element E is neither a variable nor an integer type_error(integer, E)

Portability

GNU Prolog predicate.

6.27.15 host_name/1

Templates

: host_name(?atom)

Description

host_name(HostName) unifies HostName with the name of the host machine executing the current GNU Prolog process. If the sockets are available (section 6.28.1), the name returned will be fully qualified. In that case, host_name/1 will also succeed if HostName is instantiated to the unqualified name (or an alias) of the machine.

Errors

Hostname is neither a variable nor an atom type_error(atom, HostName)

an operating system error occurs and the value of the os_error Prolog flag is error (section 6.22.1) system_error(atom explaining the error)

Portability

GNU Prolog predicate.

6.27.16 os_version/1

Templates

: os_version(?atom)

Description

os_version(OSVersion) unifies OSVersion with the operating system version of the machine executing the current GNU Prolog process.

Errors

OSVersion is neither a variable nor an atom type_error(atom, OSVersion)

an operating system error occurs and the value of the os_error Prolog flag is error (section 6.22.1) system_error(atom explaining the error)

Portability

GNU Prolog predicate.

6.27.17 architecture/1

Templates

: architecture(?atom)

Description

architecture(Architecture) unifies Architecture with the name of the machine executing the current GNU Prolog process.

Errors

Architecture is neither a variable nor an atom type_error(atom, Architecture)

an operating system error occurs and the value of the os_error Prolog flag is error (section 6.22.1) system_error(atom explaining the error)

Portability

GNU Prolog predicate.

6.27.18 shell/2, shell/1, shell/0

Templates

: shell(+atom, ?integer) shell(+atom) shell

Description

shell(Command, Status) invokes a new shell (named by the SHELL environment variable) passing Command for execution and unifies Status with the result of the execution. If Command is the empty atom '' a new interactive shell is executed. The control is returned to Prolog upon termination of the called process.

shell(Command) is equivalent to shell(Command, 0).

shell is equivalent to shell('', 0).

Errors

Command is a variable instantiation_error

Command is neither a variable nor an atom type_error(atom, Command)

Status is neither a variable nor an integer type_error(integer, Status)

Portability

GNU Prolog predicates.

6.27.19 system/2, system/1

Templates

: system(+atom, ?integer) system(+atom)

Description

system(Command, Status) invokes a new default shell passing Command for execution and unifies Status with the result of the execution. The control is returned to Prolog upon termination of the shell process. This predicate is an interface to the C Unix function system(3).

system(Command) is equivalent to system(Command, 0).

Errors

Command is a variable instantiation_error

Command is neither a variable nor an atom type_error(atom, Command)

Status is neither a variable nor an integer type_error(integer, Status)

Portability

GNU Prolog predicates.

6.27.20 spawn/3, spawn/2

Templates

: spawn(+atom, +atom_list, ?integer) spawn(+atom, +atom_list)

Description

spawn(Command, Arguments, Status) executes Command passing as arguments of the command-line each element of the list Arguments and unifies Status with the result of the execution. The control is returned to Prolog upon termination of the command.

spawn(Command, Arguments) is equivalent to spawn(Command, Arguments, 0).

Errors

Command is a variable instantiation_error

Command is neither a variable nor an atom type_error(atom, Command)

Arguments is a partial list or a list with an element which is a variable instantiation_error

Arguments is neither a partial list nor a list type_error(list, Arguments)

an element E of the Arguments list is neither a variable nor an atom type_error(atom, E)

Status is neither a variable nor an integer type_error(integer, Status)

an operating system error occurs and the value of the os_error Prolog flag is error (section 6.22.1) system_error(atom explaining the error)

Portability

GNU Prolog predicates.

6.27.21 popen/3

Templates

: popen(+atom, +io_mode, -stream)

Description

popen(Command, Mode, Stream) invokes a new default shell (by creating a pipe) passing Command for execution and associates a stream either to the standard input or the standard output of the created process. if Mode is read (resp. write) an input (resp. output) stream is created and Stream is unified with the stream-term associated. Writing to the stream writes to the standard input of the command while reading from the stream reads the command's standard output. The stream must be closed using close/2 (section 6.10.7). This predicate is an interface to the C Unix function popen(3).

Errors

Command is a variable instantiation_error

Command is neither a variable nor an atom type_error(atom, Command)

Mode is a variable instantiation_error

Mode is neither a variable nor an atom type_error(atom, Mode)

Mode is an atom but neither read nor write. domain_error(io_mode, Mode)

Stream is not a variable type_error(variable, Stream)

an operating system error occurs and the value of the os_error Prolog flag is error (section 6.22.1) system_error(atom explaining the error)

Portability

GNU Prolog predicate.

6.27.22 exec/5, exec/4

Templates

: exec(+atom, -stream, -stream, -stream, -integer) exec(+atom, -stream, -stream, -stream)

Description

exec(Command, StreamIn, StreamOut, StreamErr, Pid) invokes a new default shell passing Command for execution and associates streams to standard streams of the created process. StreamIn is unified with the stream-term associated to the standard input stream of Command (it is an output stream). StreamOut is unified with the stream-term associated to the standard output stream of Command (it is an input stream). StreamErr is unified with the stream-term associated to the standard error stream of Command (it is an input stream). Pid is unified with the process identifier of the new process. This information is only useful if it is necessary to obtain the status of the execution using wait/2 (section 6.27.23). Until a call to wait/2 is done the process remains in the system processes table (as a zombie process if terminated). For this reason, if the status is not needed it is preferable to use exec/4.

exec/4 is similar to exec/5 but the process is removed from system processes as soon as it is terminated.

Errors

Command is a variable instantiation_error

Command is neither a variable nor an atom type_error(atom, Command)

StreamIn is not a variable type_error(variable, StreamIn)

StreamOut is not a variable type_error(variable, StreamOut)

StreamErr is not a variable type_error(variable, StreamErr)

Pid is not a variable type_error(variable, Pid)

an operating system error occurs and the value of the os_error Prolog flag is error (section 6.22.1) system_error(atom explaining the error)

Portability

GNU Prolog predicates.

6.27.23 wait/2

Templates

: wait(+integer, ?integer)

Description

wait(Pid, Status) waits for the child process whose identifier is Pid to terminate. Status is then unified with the exit status. This predicate is an interface to the C Unix function waitpid(2).

Errors

Pid is a variable instantiation_error

Pid is neither a variable nor an integer type_error(integer, Pid)

Status is neither a variable nor an integer type_error(integer, Status)

an operating system error occurs and the value of the os_error Prolog flag is error (section 6.22.1) system_error(atom explaining the error)

Portability

GNU Prolog predicate.

6.27.24 prolog_pid/1

Templates

: prolog_pid(?integer)

Description

prolog_pid(Pid) unifies Pid with the process identifier of the current GNU Prolog process.

Errors

Pid is neither a variable nor an integer type_error(integer, Pid)

Portability

GNU Prolog predicate.

6.27.25 send_signal/2

Templates

: send_signal(+integer, +integer) send_signal(+integer, +atom)

Description

send_signal(Pid, Signal) sends Signal to the process whose identifier is Pid. Signal can be specified directly as an integer or symbolically as an atom. Allowed atoms depend on the machine (e.g. 'SIGINT', 'SIGQUIT', 'SIGKILL', 'SIGUSR1', 'SIGUSR2', 'SIGALRM',...). This predicate is an interface to the C Unix function kill(2).

Errors

Pid is a variable instantiation_error

Pid is neither a variable nor an integer type_error(integer, Pid)

Signal is a variable instantiation_error

Signal is neither a variable nor an integer or an atom type_error(integer, Signal)

an operating system error occurs and the value of the os_error Prolog flag is error (section 6.22.1) system_error(atom explaining the error)

Portability

GNU Prolog predicate.

6.27.26 sleep/1

Templates

: sleep(+number)

Description

sleep(Seconds) puts the GNU Prolog process to sleep for Seconds seconds. Seconds can be an integer or a floating point number (in which case it can be < 1). This predicate is an interface to the C Unix function usleep(3).

Errors

Seconds is a variable instantiation_error

Seconds is neither a variable nor a number type_error(number, Seconds)

Seconds is a number < 0 domain_error(not_less_than_zero, Seconds)

Portability

GNU Prolog predicate.

6.27.27 select/5

Templates

: select(+list, ?list, +list, ?list, +number)

Description

select(Reads, ReadyReads, Writes, ReadyWrites, TimeOut) waits for a number of streams (or file descriptors) to change status. ReadyReads is unified with the list of elements listed in Reads that have characters available for reading. Similarly ReadyWrites is unified with the list of elements of Writes that are ok for immediate writing. The elements of Reads and Writes are either stream-terms or aliases or integers considered as file descriptors, e.g. for sockets (section 6.28). Streams that must be tested with select/5 should not be buffered. This can be done at the opening using open/4 (section 6.10.6) or later using set_stream_buffering/2 (section 6.10.24). TimeOut is an upper bound on the amount of time (in milliseconds) elapsed before select/5 returns. If TimeOut £ 0 (no timeout) select/5 waits until something is available (either or reading or for writing) and thus can block indefinitely. This predicate is an interface to the C Unix function select(2).

Errors

Reads (or Writes) is a partial list or a list with an element E which is a variable instantiation_error

Reads is neither a partial list nor a list type_error(list, Reads)

Writes is neither a partial list nor a list type_error(list, Writes)

ReadyReads is neither a partial list nor a list type_error(list, ReadyReads)

ReadyWrites is neither a partial list nor a list type_error(list, ReadyWrites)

an element E of the Reads (or Writes) list is neither a stream-term or alias nor an integer domain_error(stream_or_alias, E)

an element E of the Reads (or Writes) list is not a selectable item domain_error(selectable_item, E)

an element E of the Reads (or Writes) list is an integer < 0 domain_error(not_less_than_zero, E)

an element E of the Reads (or Writes) list is a stream-tern or alias not associated with an open stream existence_error(stream, E)

an element E of the Reads list is associated to an output stream permission_error(input, stream, E)

an element E of the Writes list is associated to an input stream permission_error(output, stream, E)

TimeOut is a variable instantiation_error

TimeOut is neither a variable nor a number type_error(number, TimeOut)

an operating system error occurs and the value of the os_error Prolog flag is error (section 6.22.1) system_error(atom explaining the error)

Portability

GNU Prolog predicate.

Copyright (C) 1999,2000 Daniel Diaz

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