3.34 Operating System Interaction

shell(+Command, -Status)

Execute Command on the operating system. Command is given to the Bourne shell (/bin/sh). Status is unified with the exit status of the command.

On Win32 systems, shell/[1,2] executes the command using the CreateProcess() API and waits for the command to terminate. If the command ends with a & sign, the command is handed to the WinExec() API, which does not wait for the new task to terminate. See also win_exec/2.

shell(+Command)

Equivalent to `shell(Command, 0)'.

shell

Start an interactive Unix shell. Default is /bin/sh, the environment variable SHELL overrides this default. Not available for Win32 platforms.

win_exec(+Command, +Show)

Win32 systems only. Spawns a Windows task without waiting for its completion. Show is either iconic or normal and dictates the initial status of the window. The iconic option is notably handy to start (DDE) servers.

getenv(+Name, -Value)

Get environment variable. Fails silently if the variable does not exist. Please note that environment variable names are case-sensitive on Unix systems and case-insensitive on Windows.

setenv(+Name, +Value)

Set environment variable. Name and Value should be instantiated to atoms or integers. The environment variable will be passed to shell/[0-2] and can be requested using getenv/2. They also influence expand_file_name/2.

unsetenv(+Name)

Remove environment variable from the environment.

unix(+Command)

This predicate comes from the Quintus compatibility library and provides a partial implementation thereof. It provides access to some operating system features and unlike the name suggests, is not operating system specific. Currently it is the only way to fetch the Prolog command-line arguments. Defined Command's are below.

system(+Command)

Equivalent to calling shell/1. Use for compatibility only.

shell(+Command)

Equivalent to calling shell/1. Use for compatibility only.

shell

Equivalent to calling shell/0. Use for compatibility only.

cd

Equivalent to calling chdir/1 as chdir(~). Use for compatibility only.

cd(+Directory)

Equivalent to calling chdir/1. Use for compatibility only.

argv(-Argv)

Unify Argv with the list of commandline arguments provides to this Prolog run. Please note that Prolog system-arguments and application arguments are separated by --. Integer arguments are passed as Prolog integers, float arguments and Prolog floating point numbers and all other arguments as Prolog atoms.

A stand-alone program could use the following skeleton to handle command-line arguments. See also section 2.10.2.3.

main :- unix(argv(Argv)), append(_PrologArgs, [--|AppArgs], Argv), !, main(AppArgs).

get_time(-Time)

Return the number of seconds that elapsed since the epoch of Unix, 1 January 1970, 0 hours. Time is a floating point number. Its granularity is system dependent. On SUN, this is 1/60 of a second.

convert_time(+Time, -Year, -Month, -Day, -Hour, -Minute, -Second, -MilliSeconds)

Convert a time stamp, provided by get_time/1, time_file/2, etc. Year is unified with the year, Month with the month number (January is 1), Day with the day of the month (starting with 1), Hour with the hour of the day (0--23), Minute with the minute (0--59). Second with the second (0--59) and MilliSecond with the milliseconds (0--999). Note that the latter might not be accurate or might always be 0, depending on the timing capabilities of the system. See also convert_time/2.

convert_time(+Time, -String)

Convert a time-stamp as obtained though get_time/1 into a textual representation using the C-library function ctime(). The value is returned as a SWI-Prolog string object (see section 3.21). See also convert_time/8.