Scala includes a process library to simplify working with external
processes. Use import scala.sys.process._ to bring the implicit
conversions into scope.
To run an external command, follow it with an exclamation mark !:
"find project -name *.jar" !
An implicit converts the String to scala.sys.process.ProcessBuilder,
which defines the ! method. This method runs the constructed command,
waits until the command completes, and returns the exit code.
Alternatively, the run method defined on ProcessBuilder runs the
command and returns an instance of scala.sys.process.Process, which
can be used to destroy the process before it completes. With no
arguments, the ! method sends output to standard output and standard
error. You can pass a Logger to the ! method to send output to the
Logger:
"find project -name *.jar" ! log
You can get a Logger with:
val log = streams.value.log
If you need to set the working directory or modify the environment, call
scala.sys.process.Process explicitly, passing the command sequence
(command and argument list) or command string first and the working
directory second. Any environment variables can be passed as a vararg
list of key/value String pairs.
Process("ls" :: "-l" :: Nil, Path.userHome, "key1" -> value1, "key2" -> value2) ! log
Operators are defined to combine commands. These operators start with
# in order to keep the precedence the same and to separate them from
the operators defined elsewhere in sbt for filters. In the following
operator definitions, a and b are subcommands.
a #&& b Execute a. If the exit code is nonzero, return that exit
code and do not execute b. If the exit code is zero, execute b and
return its exit code.
a #|| b Execute a. If the exit code is zero, return zero for the
exit code and do not execute b. If the exit code is nonzero, execute
b and return its exit code.
a #| b Execute a and b, piping the output of a to the input
of b.
There are also operators defined for redirecting output to Files and
input from Files and URLs. In the following definitions, url is an
instance of URL and file is an instance of File.
a #< url or url #> a Use url as the input to a. a may be a
File or a command.
a #< file or file #> a Use file as the input to a. a may be
a File or a command.
a #> file or file #< a Write the output of a to file. a may
be a File, URL, or a command.
a #>> file or file #<< a Append the output of a to file. a may
be a File, URL, or a command.
There are some additional methods to get the output from a forked
process into a String or the output lines as a Stream[String]. Here
are some examples, but see the
ProcessBuilder API for details.
val listed: String = "ls" !!
val lines2: Stream[String] = "ls" lines_!
Finally, there is a cat method to send the contents of Files and
URLs to standard output.
Download a URL to a File:
url("http://databinder.net/dispatch/About") #> file("About.html") !
// or
file("About.html") #< url("http://databinder.net/dispatch/About") !
Copy a File:
file("About.html") #> file("About_copy.html") !
// or
file("About_copy.html") #< file("About.html") !
Append the contents of a URL to a File after filtering through
grep:
url("http://databinder.net/dispatch/About") #> "grep JSON" #>> file("About_JSON") !
// or
file("About_JSON") #<< ( "grep JSON" #< url("http://databinder.net/dispatch/About") ) !
Search for uses of null in the source directory:
"find src -name *.scala -exec grep null {} ;" #| "xargs test -z" #&& "echo null-free" #|| "echo null detected" !
Use cat:
val spde = url("http://technically.us/spde/About")
val dispatch = url("http://databinder.net/dispatch/About")
val build = file("project/build.properties")
cat(spde, dispatch, build) #| "grep -i scala" !
