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.TH os 3 "kernel 2.12.3" "Ericsson AB" "ERLANG MODULE DEFINITION"
.SH MODULE
os \- Operating System Specific Functions
.SH DESCRIPTION
.LP
The functions in this module are operating system specific\&. Careless use of these functions will result in programs that will only run on a specific platform\&. On the other hand, with careful use these functions can be of help in enabling a program to run on most platforms\&.
.SH EXPORTS
.LP
.B
cmd(Command) -> string()
.br
.RS
.TP
Types
Command = string() | atom()
.br
.RE
.RS
.LP
Executes \fICommand\fR in a command shell of the target OS, captures the standard output of the command and returns this result as a string\&. This function is a replacement of the previous \fIunix:cmd/1\fR; on a Unix platform they are equivalent\&.
.LP
Examples:
.nf
LsOut = os:cmd("ls"), % on unix platform
DirOut = os:cmd("dir"), % on Win32 platform
.fi
.LP
Note that in some cases, standard output of a command when called from another program (for example, \fIos:cmd/1\fR) may differ, compared to the standard output of the command when called directly from an OS command shell\&.
.RE
.LP
.B
find_executable(Name) -> Filename | false
.br
.B
find_executable(Name, Path) -> Filename | false
.br
.RS
.TP
Types
Name = string()
.br
Path = string()
.br
Filename = string()
.br
.RE
.RS
.LP
These two functions look up an executable program given its name and a search path, in the same way as the underlying operating system\&. \fIfind_executable/1\fR uses the current execution path (that is, the environment variable PATH on Unix and Windows)\&.
.LP
\fIPath\fR, if given, should conform to the syntax of execution paths on the operating system\&. The absolute filename of the executable program \fIName\fR is returned, or \fIfalse\fR if the program was not found\&.
.RE
.LP
.B
getenv() -> [string()]
.br
.RS
.LP
Returns a list of all environement variables\&. Each environment variable is given as a single string on the format \fI"VarName=Value"\fR, where \fIVarName\fR is the name of the variable and \fIValue\fR its value\&.
.RE
.LP
.B
getenv(VarName) -> Value | false
.br
.RS
.TP
Types
VarName = string()
.br
Value = string()
.br
.RE
.RS
.LP
Returns the \fIValue\fR of the environment variable \fIVarName\fR, or \fIfalse\fR if the environment variable is undefined\&.
.RE
.LP
.B
getpid() -> Value
.br
.RS
.TP
Types
Value = string()
.br
.RE
.RS
.LP
Returns the process identifier of the current Erlang emulator in the format most commonly used by the operating system environment\&. \fIValue\fR is returned as a string containing the (usually) numerical identifier for a process\&. On Unix, this is typically the return value of the \fIgetpid()\fR system call\&. On VxWorks, \fIValue\fR contains the task id (decimal notation) of the Erlang task\&. On Windows, the process id as returned by the \fIGetCurrentProcessId()\fR system call is used\&.
.RE
.LP
.B
putenv(VarName, Value) -> true
.br
.RS
.TP
Types
VarName = string()
.br
Value = string()
.br
.RE
.RS
.LP
Sets a new \fIValue\fR for the environment variable \fIVarName\fR\&.
.RE
.LP
.B
type() -> {Osfamily, Osname} | Osfamily
.br
.RS
.TP
Types
Osfamily = win32 | unix | vxworks
.br
Osname = atom()
.br
.RE
.RS
.LP
Returns the \fIOsfamily\fR and, in some cases, \fIOsname\fR of the current operating system\&.
.LP
On Unix, \fIOsname\fR will have same value as \fIuname -s\fR returns, but in lower case\&. For example, on Solaris 1 and 2, it will be \fIsunos\fR\&.
.LP
In Windows, \fIOsname\fR will be either \fInt\fR (on Windows NT), or \fIwindows\fR (on Windows 95)\&.
.LP
On VxWorks the OS family alone is returned, that is \fIvxworks\fR\&.
.SS Note:
.LP
Think twice before using this function\&. Use the \fIfilename\fR module if you want to inspect or build file names in a portable way\&. Avoid matching on the \fIOsname\fR atom\&.
.RE
.LP
.B
version() -> {Major, Minor, Release} | VersionString
.br
.RS
.TP
Types
Major = Minor = Release = integer()
.br
VersionString = string()
.br
.RE
.RS
.LP
Returns the operating system version\&. On most systems, this function returns a tuple, but a string will be returned instead if the system has versions which cannot be expressed as three numbers\&.
.SS Note:
.LP
Think twice before using this function\&. If you still need to use it, always \fIcall os:type()\fR first\&.
.RE
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