I run some commands in terminal with this code:
system("the command here")
And after I want to know what is the result of running this command, e.g. if I run
system("git status")
I want to read the actual information about changes in my repo. Is there any way to do that in swift?
NSTask
is class to run another program as a subprocess. You can
capture the program's output, error output, exit status and much more.
Expanding on my answer to xcode 6 swift system() command, here is a simple utility function to run a command synchronously, and return the output, error output and exit code (now updated for Swift 2):
func runCommand(cmd : String, args : String...) -> (output: [String], error: [String], exitCode: Int32) {
var output : [String] = []
var error : [String] = []
let task = NSTask()
task.launchPath = cmd
task.arguments = args
let outpipe = NSPipe()
task.standardOutput = outpipe
let errpipe = NSPipe()
task.standardError = errpipe
task.launch()
let outdata = outpipe.fileHandleForReading.readDataToEndOfFile()
if var string = String.fromCString(UnsafePointer(outdata.bytes)) {
string = string.stringByTrimmingCharactersInSet(NSCharacterSet.newlineCharacterSet())
output = string.componentsSeparatedByString("\n")
}
let errdata = errpipe.fileHandleForReading.readDataToEndOfFile()
if var string = String.fromCString(UnsafePointer(errdata.bytes)) {
string = string.stringByTrimmingCharactersInSet(NSCharacterSet.newlineCharacterSet())
error = string.componentsSeparatedByString("\n")
}
task.waitUntilExit()
let status = task.terminationStatus
return (output, error, status)
}
Sample usage:
let (output, error, status) = runCommand("/usr/bin/git", args: "status")
print("program exited with status \(status)")
if output.count > 0 {
print("program output:")
print(output)
}
if error.count > 0 {
print("error output:")
print(error)
}
Or, if you are only interested in the output, but not in the error messages or exit code:
let output = runCommand("/usr/bin/git", args: "status").output
Output and error output are returned as an array of strings, one string for each line.
The first argument to runCommand()
must be the full path to an
executable, such as "/usr/bin/git"
. You can start the program using a shell (which is what system()
also does):
let (output, error, status) = runCommand("/bin/sh", args: "-c", "git status")
The advantage is that the "git" executable is automatically found via the default search path. The disadvantage is that you have to quote/escape arguments correctly if they contain spaces or other characters which have a special meaning in the shell.
Update for Swift 3:
func runCommand(cmd : String, args : String...) -> (output: [String], error: [String], exitCode: Int32) {
var output : [String] = []
var error : [String] = []
let task = Process()
task.launchPath = cmd
task.arguments = args
let outpipe = Pipe()
task.standardOutput = outpipe
let errpipe = Pipe()
task.standardError = errpipe
task.launch()
let outdata = outpipe.fileHandleForReading.readDataToEndOfFile()
if var string = String(data: outdata, encoding: .utf8) {
string = string.trimmingCharacters(in: .newlines)
output = string.components(separatedBy: "\n")
}
let errdata = errpipe.fileHandleForReading.readDataToEndOfFile()
if var string = String(data: errdata, encoding: .utf8) {
string = string.trimmingCharacters(in: .newlines)
error = string.components(separatedBy: "\n")
}
task.waitUntilExit()
let status = task.terminationStatus
return (output, error, status)
}
system
spawns a new process so you can’t capture its ouput. The equivalent that gives you a way to do this would be popen
, which you could use like this:
import Darwin
let fp = popen("ping -c 4 localhost", "r")
var buf = Array<CChar>(count: 128, repeatedValue: 0)
while fgets(&buf, CInt(buf.count), fp) != nil,
let str = String.fromCString(buf) {
print(str)
}
fclose(fp)
However, don’t do it this way. Use NSTask
as Martin describes.
edit: based on your request to run multiple commands in parallel, here is some probably-unwise code:
import Darwin
let commands = [
"tail /etc/hosts",
"ping -c 2 localhost",
]
let fps = commands.map { popen($0, "r") }
var buf = Array<CChar>(count: 128, repeatedValue: 0)
let results: [String] = fps.map { fp in
var result = ""
while fgets(&buf, CInt(buf.count), fp) != nil,
let str = String.fromCString(buf) {
result += str
}
return result
}
fps.map { fclose($0) }
println("\n\n----\n\n".join(map(zip(commands,results)) { "\($0):\n\($1)" }))
(seriously, use NSTask
)
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