This class implements the File
Transfer Protocol. If you have used a command-line FTP
program, and are familiar with the commands, you will be able to use this class easily. Some extra features are included to take advantage of Ruby’s style and strengths.
Example
require 'net/ftp'
Example 1
ftp = Net::FTP.new('example.com') ftp.login files = ftp.chdir('pub/lang/ruby/contrib') files = ftp.list('n*') ftp.getbinaryfile('nif.rb-0.91.gz', 'nif.gz', 1024) ftp.close
Example 2
Net::FTP.open('example.com') do |ftp| ftp.login files = ftp.chdir('pub/lang/ruby/contrib') files = ftp.list('n*') ftp.getbinaryfile('nif.rb-0.91.gz', 'nif.gz', 1024) end
Major Methods
The following are the methods most likely to be useful to users:
When true
, transfers are performed in binary mode. Default: true
.
When true
, the connection is in passive mode. Default: true
.
When true
, all traffic to and from the server is written to +$stdout+. Default: false
.
Sets or retrieves the resume
status, which decides whether incomplete transfers are resumed or restarted. Default: false
.
Number of seconds to wait for the connection to open. Any number may be used, including Floats for fractional seconds. If the FTP
object cannot open a connection in this many seconds, it raises a Net::OpenTimeout
exception. The default value is nil
.
Number of seconds to wait for the TLS handshake. Any number may be used, including Floats for fractional seconds. If the FTP
object cannot complete the TLS handshake in this many seconds, it raises a Net::OpenTimeout
exception. The default value is nil
. If ssl_handshake_timeout
is nil
, open_timeout
is used instead.
Number of seconds to wait for one block to be read (via one read(2) call). Any number may be used, including Floats for fractional seconds. If the FTP
object cannot read data in this many seconds, it raises a Timeout::Error
exception. The default value is 60 seconds.
The server’s welcome message.
The server’s last response code.
The server’s last response code.
The server’s last response.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 151
def self.default_passive
@@default_passive
end
When true
, connections are in passive mode per default. Default: true
.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 145
def self.default_passive=(value)
@@default_passive = value
end
When true
, connections are in passive mode per default. Default: true
.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 211
def initialize(host = nil, user_or_options = {}, passwd = nil, acct = nil)
super()
begin
options = user_or_options.to_hash
rescue NoMethodError
# for backward compatibility
options = {}
options[:username] = user_or_options
options[:password] = passwd
options[:account] = acct
end
@host = nil
if options[:ssl]
unless defined?(OpenSSL::SSL)
raise "SSL extension not installed"
end
ssl_params = options[:ssl] == true ? {} : options[:ssl]
@ssl_context = SSLContext.new
@ssl_context.set_params(ssl_params)
if defined?(VerifyCallbackProc)
@ssl_context.verify_callback = VerifyCallbackProc
end
@ssl_session = nil
if options[:private_data_connection].nil?
@private_data_connection = true
else
@private_data_connection = options[:private_data_connection]
end
else
@ssl_context = nil
if options[:private_data_connection]
raise ArgumentError,
"private_data_connection can be set to true only when ssl is enabled"
end
@private_data_connection = false
end
@binary = true
if options[:passive].nil?
@passive = @@default_passive
else
@passive = options[:passive]
end
if options[:debug_mode].nil?
@debug_mode = false
else
@debug_mode = options[:debug_mode]
end
@resume = false
@bare_sock = @sock = NullSocket.new
@logged_in = false
@open_timeout = options[:open_timeout]
@ssl_handshake_timeout = options[:ssl_handshake_timeout]
@read_timeout = options[:read_timeout] || 60
if host
if options[:port]
connect(host, options[:port] || FTP_PORT)
else
# spec/rubyspec/library/net/ftp/initialize_spec.rb depends on
# the number of arguments passed to connect....
connect(host)
end
if options[:username]
login(options[:username], options[:password], options[:account])
end
end
end
Creates and returns a new FTP
object. If a host
is given, a connection is made.
options
is an option hash, each key of which is a symbol.
The available options are:
- port
-
Port number (default value is 21)
- ssl
-
If options is true, then an attempt will be made to use SSL (now TLS) to connect to the server. For this to work
OpenSSL
[OSSL] and the RubyOpenSSL
[RSSL] extensions need to be installed. If options is a hash, it’s passed toOpenSSL::SSL::SSLContext#set_params
as parameters. - private_data_connection
-
If true, TLS is used for data connections. Default:
true
when options is true. - username
-
Username for login. If options is the string “anonymous” and the options is
nil
, “anonymous@” is used as a password. - password
-
Password for login.
- account
-
Account information for ACCT.
- passive
-
When
true
, the connection is in passive mode. Default:true
. open_timeout
-
Number of seconds to wait for the connection to open. See
Net::FTP#open_timeout
for details. Default:nil
. read_timeout
-
Number of seconds to wait for one block to be read. See
Net::FTP#read_timeout
for details. Default:60
. ssl_handshake_timeout
-
Number of seconds to wait for the TLS handshake. See
Net::FTP#ssl_handshake_timeout
for details. Default:nil
. debug_mode
-
When
true
, all traffic to and from the server is written to +$stdout+. Default:false
.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 161
def FTP.open(host, *args)
if block_given?
ftp = new(host, *args)
begin
yield ftp
ensure
ftp.close
end
else
new(host, *args)
end
end
A synonym for FTP.new
, but with a mandatory host parameter.
If a block is given, it is passed the FTP
object, which will be closed when the block finishes, or when an exception is raised.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1229
def abort
line = "ABOR" + CRLF
print "put: ABOR\n" if @debug_mode
@sock.send(line, Socket::MSG_OOB)
resp = getmultiline
unless ["426", "226", "225"].include?(resp[0, 3])
raise FTPProtoError, resp
end
return resp
end
Aborts the previous command (ABOR command).
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 882
def acct(account)
cmd = "ACCT " + account
voidcmd(cmd)
end
Sends the ACCT command.
This is a less common FTP
command, to send account information if the destination host requires it.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 280
def binary=(newmode)
if newmode != @binary
@binary = newmode
send_type_command if @logged_in
end
end
A setter to toggle transfers in binary mode. newmode
is either true
or false
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1150
def chdir(dirname)
if dirname == ".."
begin
voidcmd("CDUP")
return
rescue FTPPermError => e
if e.message[0, 3] != "500"
raise e
end
end
end
cmd = "CWD #{dirname}"
voidcmd(cmd)
end
Changes the (remote) directory.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1307
def close
if @sock and not @sock.closed?
begin
@sock.shutdown(Socket::SHUT_WR) rescue nil
orig, self.read_timeout = self.read_timeout, 3
@sock.read rescue nil
ensure
@sock.close
self.read_timeout = orig
end
end
end
Closes the connection. Further operations are impossible until you open a new connection with connect
.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1323
def closed?
@sock == nil or @sock.closed?
end
Returns true
iff the connection is closed.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 369
def connect(host, port = FTP_PORT)
if @debug_mode
print "connect: ", host, ", ", port, "\n"
end
synchronize do
@host = host
@bare_sock = open_socket(host, port)
@sock = BufferedSocket.new(@bare_sock, read_timeout: @read_timeout)
voidresp
if @ssl_context
begin
voidcmd("AUTH TLS")
ssl_sock = start_tls_session(@bare_sock)
@sock = BufferedSSLSocket.new(ssl_sock, read_timeout: @read_timeout)
if @private_data_connection
voidcmd("PBSZ 0")
voidcmd("PROT P")
end
rescue OpenSSL::SSL::SSLError, OpenTimeout
@sock.close
raise
end
end
end
end
Establishes an FTP
connection to host, optionally overriding the default port. If the environment variable SOCKS_SERVER
is set, sets up the connection through a SOCKS proxy. Raises an exception (typically Errno::ECONNREFUSED
) if the connection cannot be established.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1136
def delete(filename)
resp = sendcmd("DELE #{filename}")
if resp.start_with?("250")
return
elsif resp.start_with?("5")
raise FTPPermError, resp
else
raise FTPReplyError, resp
end
end
Deletes a file on the server.
get(remotefile, localfile = File.basename(remotefile), blocksize = DEFAULT_BLOCKSIZE) { |data| ... }
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 811
def get(remotefile, localfile = File.basename(remotefile),
blocksize = DEFAULT_BLOCKSIZE, &block) # :yield: data
if @binary
getbinaryfile(remotefile, localfile, blocksize, &block)
else
gettextfile(remotefile, localfile, &block)
end
end
Retrieves remotefile
in whatever mode the session is set (text or binary). See gettextfile
and getbinaryfile
.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 750
def getbinaryfile(remotefile, localfile = File.basename(remotefile),
blocksize = DEFAULT_BLOCKSIZE, &block) # :yield: data
f = nil
result = nil
if localfile
if @resume
rest_offset = File.size?(localfile)
f = File.open(localfile, "a")
else
rest_offset = nil
f = File.open(localfile, "w")
end
elsif !block_given?
result = String.new
end
begin
f&.binmode
retrbinary("RETR #{remotefile}", blocksize, rest_offset) do |data|
f&.write(data)
block&.(data)
result&.concat(data)
end
return result
ensure
f&.close
end
end
Retrieves remotefile
in binary mode, storing the result in localfile
. If localfile
is nil, returns retrieved data. If a block is supplied, it is passed the retrieved data in blocksize
chunks.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 785
def gettextfile(remotefile, localfile = File.basename(remotefile),
&block) # :yield: line
f = nil
result = nil
if localfile
f = File.open(localfile, "w")
elsif !block_given?
result = String.new
end
begin
retrlines("RETR #{remotefile}") do |line, newline|
l = newline ? line + "\n" : line
f&.print(l)
block&.(line, newline)
result&.concat(l)
end
return result
ensure
f&.close
end
end
Retrieves remotefile
in ASCII (text) mode, storing the result in localfile
. If localfile
is nil, returns retrieved data. If a block is supplied, it is passed the retrieved data one line at a time.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1271
def help(arg = nil)
cmd = "HELP"
if arg
cmd = cmd + " " + arg
end
sendcmd(cmd)
end
Issues the HELP command.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 906
def list(*args, &block) # :yield: line
cmd = "LIST"
args.each do |arg|
cmd = "#{cmd} #{arg}"
end
lines = []
retrlines(cmd) do |line|
lines << line
end
if block
lines.each(&block)
end
return lines
end
Returns an array of file information in the directory (the output is like ‘ls -l`). If a block is given, it iterates through the listing.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 601
def login(user = "anonymous", passwd = nil, acct = nil)
if user == "anonymous" and passwd == nil
passwd = "anonymous@"
end
resp = ""
synchronize do
resp = sendcmd('USER ' + user)
if resp.start_with?("3")
raise FTPReplyError, resp if passwd.nil?
resp = sendcmd('PASS ' + passwd)
end
if resp.start_with?("3")
raise FTPReplyError, resp if acct.nil?
resp = sendcmd('ACCT ' + acct)
end
end
if !resp.start_with?("2")
raise FTPReplyError, resp
end
@welcome = resp
send_type_command
@logged_in = true
end
Logs in to the remote host. The session must have been previously connected. If user
is the string “anonymous” and the password
is nil
, “anonymous@” is used as a password. If the acct
parameter is not nil
, an FTP
ACCT command is sent following the successful login. Raises an exception on error (typically Net::FTPPermError
).
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1261
def mdtm(filename)
resp = sendcmd("MDTM #{filename}")
if resp.start_with?("213")
return get_body(resp)
end
end
Returns the raw last modification time of the (remote) file in the format “YYYYMMDDhhmmss” (MDTM command).
Use mtime
if you want a parsed Time
instance.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1194
def mkdir(dirname)
resp = sendcmd("MKD #{dirname}")
return parse257(resp)
end
Creates a remote directory.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1110
def mlsd(pathname = nil, &block) # :yield: entry
cmd = pathname ? "MLSD #{pathname}" : "MLSD"
entries = []
retrlines(cmd) do |line|
entries << parse_mlsx_entry(line)
end
if block
entries.each(&block)
end
return entries
end
Returns an array of the entries of the directory specified by pathname
. Each entry has the facts (e.g., size, last modification time, etc.) and the pathname. If a block is given, it iterates through the listing. If pathname
is omitted, the current directory is assumed.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1088
def mlst(pathname = nil)
cmd = pathname ? "MLST #{pathname}" : "MLST"
resp = sendcmd(cmd)
if !resp.start_with?("250")
raise FTPReplyError, resp
end
line = resp.lines[1]
unless line
raise FTPProtoError, resp
end
entry = line.sub(/\A(250-| *)/, "")
return parse_mlsx_entry(entry)
end
Returns data (e.g., size, last modification time, entry type, etc.) about the file or directory specified by pathname
. If pathname
is omitted, the current directory is assumed.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1187
def mtime(filename, local = false)
return TIME_PARSER.(mdtm(filename), local)
end
Returns the last modification time of the (remote) file. If local
is true
, it is returned as a local time, otherwise it’s a UTC time.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 890
def nlst(dir = nil)
cmd = "NLST"
if dir
cmd = "#{cmd} #{dir}"
end
files = []
retrlines(cmd) do |line|
files.push(line)
end
return files
end
Returns an array of filenames in the remote directory.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1291
def noop
voidcmd("NOOP")
end
Issues a NOOP command.
Does nothing except return a response.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1068
def parse_mlsx_entry(entry)
facts, pathname = entry.chomp.split(/ /, 2)
unless pathname
raise FTPProtoError, entry
end
return MLSxEntry.new(
facts.scan(/(.*?)=(.*?);/).each_with_object({}) {
|(factname, value), h|
name = factname.downcase
h[name] = FACT_PARSERS[name].(value)
},
pathname)
end
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1361
def parse_pasv_ipv4_host(s)
return s.tr(",", ".")
end
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1366
def parse_pasv_ipv6_host(s)
return s.split(/,/).map { |i|
"%02x" % i.to_i
}.each_slice(2).map(&:join).join(":")
end
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1373
def parse_pasv_port(s)
return s.split(/,/).map(&:to_i).inject { |x, y|
(x << 8) + y
}
end
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 867
def put(localfile, remotefile = File.basename(localfile),
blocksize = DEFAULT_BLOCKSIZE, &block)
if @binary
putbinaryfile(localfile, remotefile, blocksize, &block)
else
puttextfile(localfile, remotefile, &block)
end
end
Transfers localfile
to the server in whatever mode the session is set (text or binary). See puttextfile
and putbinaryfile
.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 825
def putbinaryfile(localfile, remotefile = File.basename(localfile),
blocksize = DEFAULT_BLOCKSIZE, &block) # :yield: data
if @resume
begin
rest_offset = size(remotefile)
rescue Net::FTPPermError
rest_offset = nil
end
else
rest_offset = nil
end
f = File.open(localfile)
begin
f.binmode
if rest_offset
storbinary("APPE #{remotefile}", f, blocksize, rest_offset, &block)
else
storbinary("STOR #{remotefile}", f, blocksize, rest_offset, &block)
end
ensure
f.close
end
end
Transfers localfile
to the server in binary mode, storing the result in remotefile
. If a block is supplied, calls it, passing in the transmitted data in blocksize
chunks.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 854
def puttextfile(localfile, remotefile = File.basename(localfile), &block) # :yield: line
f = File.open(localfile)
begin
storlines("STOR #{remotefile}", f, &block)
ensure
f.close
end
end
Transfers localfile
to the server in ASCII (text) mode, storing the result in remotefile
. If callback or an associated block is supplied, calls it, passing in the transmitted data one line at a time.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1209
def pwd
resp = sendcmd("PWD")
return parse257(resp)
end
Returns the current remote directory.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1282
def quit
voidcmd("QUIT")
end
Exits the FTP
session.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 128
def read_timeout=(sec)
@sock.read_timeout = sec
@read_timeout = sec
end
Setter for the read_timeout
attribute.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1125
def rename(fromname, toname)
resp = sendcmd("RNFR #{fromname}")
if !resp.start_with?("3")
raise FTPReplyError, resp
end
voidcmd("RNTO #{toname}")
end
Renames a file on the server.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 632
def retrbinary(cmd, blocksize, rest_offset = nil) # :yield: data
synchronize do
with_binary(true) do
begin
conn = transfercmd(cmd, rest_offset)
loop do
data = conn.read(blocksize)
break if data == nil
yield(data)
end
conn.shutdown(Socket::SHUT_WR)
conn.read_timeout = 1
conn.read
ensure
conn.close if conn
end
voidresp
end
end
end
Puts the connection into binary (image) mode, issues the given command, and fetches the data returned, passing it to the associated block in chunks of blocksize
characters. Note that cmd
is a server command (such as “RETR myfile”).
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 659
def retrlines(cmd) # :yield: line
synchronize do
with_binary(false) do
begin
conn = transfercmd(cmd)
loop do
line = conn.gets
break if line == nil
yield(line.sub(/\r?\n\z/, ""), !line.match(/\n\z/).nil?)
end
conn.shutdown(Socket::SHUT_WR)
conn.read_timeout = 1
conn.read
ensure
conn.close if conn
end
voidresp
end
end
end
Puts the connection into ASCII (text) mode, issues the given command, and passes the resulting data, one line at a time, to the associated block. If no block is given, prints the lines. Note that cmd
is a server command (such as “RETR myfile”).
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1202
def rmdir(dirname)
voidcmd("RMD #{dirname}")
end
Removes a remote directory.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 494
def sendcmd(cmd)
synchronize do
putline(cmd)
return getresp
end
end
Sends a command and returns the response.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 399
def set_socket(sock, get_greeting = true)
synchronize do
@sock = sock
if get_greeting
voidresp
end
end
end
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1298
def site(arg)
cmd = "SITE " + arg
voidcmd(cmd)
end
Issues a SITE command.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1173
def size(filename)
with_binary(true) do
resp = sendcmd("SIZE #{filename}")
if !resp.start_with?("213")
raise FTPReplyError, resp
end
return get_body(resp).to_i
end
end
Returns the size of the given (remote) filename.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 345
def start_tls_session(sock)
ssl_sock = SSLSocket.new(sock, @ssl_context)
ssl_sock.sync_close = true
ssl_sock.hostname = @host if ssl_sock.respond_to? :hostname=
if @ssl_session &&
Process.clock_gettime(Process::CLOCK_REALTIME) < @ssl_session.time.to_f + @ssl_session.timeout
# ProFTPD returns 425 for data connections if session is not reused.
ssl_sock.session = @ssl_session
end
ssl_socket_connect(ssl_sock, @ssl_handshake_timeout || @open_timeout)
if @ssl_context.verify_mode != VERIFY_NONE
ssl_sock.post_connection_check(@host)
end
@ssl_session = ssl_sock.session
return ssl_sock
end
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1245
def status(pathname = nil)
line = pathname ? "STAT #{pathname}" : "STAT"
if /[\r\n]/ =~ line
raise ArgumentError, "A line must not contain CR or LF"
end
print "put: #{line}\n" if @debug_mode
@sock.send(line + CRLF, Socket::MSG_OOB)
return getresp
end
Returns the status (STAT command). pathname - when stat is invoked with pathname as a parameter it acts like
list but alot faster and over the same tcp session.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 686
def storbinary(cmd, file, blocksize, rest_offset = nil) # :yield: data
if rest_offset
file.seek(rest_offset, IO::SEEK_SET)
end
synchronize do
with_binary(true) do
conn = transfercmd(cmd)
loop do
buf = file.read(blocksize)
break if buf == nil
conn.write(buf)
yield(buf) if block_given?
end
conn.close
voidresp
end
end
rescue Errno::EPIPE
# EPIPE, in this case, means that the data connection was unexpectedly
# terminated. Rather than just raising EPIPE to the caller, check the
# response on the control connection. If getresp doesn't raise a more
# appropriate exception, re-raise the original exception.
getresp
raise
end
Puts the connection into binary (image) mode, issues the given server-side command (such as “STOR myfile”), and sends the contents of the file named file
to the server. If the optional block is given, it also passes it the data, in chunks of blocksize
characters.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 718
def storlines(cmd, file) # :yield: line
synchronize do
with_binary(false) do
conn = transfercmd(cmd)
loop do
buf = file.gets
break if buf == nil
if buf[-2, 2] != CRLF
buf = buf.chomp + CRLF
end
conn.write(buf)
yield(buf) if block_given?
end
conn.close
voidresp
end
end
rescue Errno::EPIPE
# EPIPE, in this case, means that the data connection was unexpectedly
# terminated. Rather than just raising EPIPE to the caller, check the
# response on the control connection. If getresp doesn't raise a more
# appropriate exception, re-raise the original exception.
getresp
raise
end
Puts the connection into ASCII (text) mode, issues the given server-side command (such as “STOR myfile”), and sends the contents of the file named file
to the server, one line at a time. If the optional block is given, it also passes it the lines.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 1218
def system
resp = sendcmd("SYST")
if !resp.start_with?("215")
raise FTPReplyError, resp
end
return get_body(resp)
end
Returns system information.
# File tmp/rubies/ruby-2.4.10/lib/net/ftp.rb, line 504
def voidcmd(cmd)
synchronize do
putline(cmd)
voidresp
end
end
Sends a command and expect a response beginning with ‘2’.