Tcl

SSH Parallel Remote Commands on a Single Server

Demonstrates running several commands in parallel on one SSH server and collecting each command's output as it finishes. QuickCmdSend starts each command and returns immediately; QuickCmdCheck reports them as they complete.

Background: Because SSH multiplexes channels, several commands can run at once over one authenticated connection — far faster than running them one after another when each involves waiting. Results arrive in completion order rather than the order the commands were started, so the loop keys off the returned channel number. Distinguish the two negative returns carefully: -1 means "still working, ask again," while -2 means nothing remains to collect or the connection failed.

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Tcl


load ./chilkat.dll

set success 0

#  This example requires the Chilkat API to have been previously unlocked.
#  See Global Unlock Sample for sample code.

#  Demonstrates running several commands in parallel on a single SSH server and collecting each
#  command's output as it finishes.

set ssh [new_CkSsh]

set port 22
set success [CkSsh_Connect $ssh "ssh.example.com" $port]
if {$success == 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

#  Normally you would not hard-code the password in source.  You should instead obtain it
#  from an interactive prompt, environment variable, or a secrets vault.
set password "mySshPassword"

set success [CkSsh_AuthenticatePw $ssh "mySshLogin" $password]
if {$success == 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

#  QuickCmdSend starts a command and returns immediately, so all three run concurrently, each on
#  its own session channel.
set channel1 [CkSsh_QuickCmdSend $ssh "df"]
if {$channel1 < 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

set channel2 [CkSsh_QuickCmdSend $ssh "date"]
if {$channel2 < 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

set channel3 [CkSsh_QuickCmdSend $ssh "echo hello world"]
if {$channel3 < 0} then {
    puts [CkSsh_lastErrorText $ssh]
    delete_CkSsh $ssh
    exit
}

#  Collect the results.  QuickCmdCheck returns the channel number of a completed command,
#  -1 when commands are still pending but none finished within the timeout, or -2 when nothing
#  remains to be checked (or an error occurred).
set pollTimeoutMs 50
set numFinished 0
while {$numFinished < 3} {
    set channel [CkSsh_QuickCmdCheck $ssh $pollTimeoutMs]
    if {$channel == -2} then {
        puts [CkSsh_lastErrorText $ssh]
        delete_CkSsh $ssh
        exit
    }

    if {$channel >= 0} then {
        puts "---- channel $channel finished ----"
        set cmdOutput [CkSsh_getReceivedText $ssh $channel "utf-8"]
        if {[CkSsh_get_LastMethodSuccess $ssh] == 0} then {
            puts [CkSsh_lastErrorText $ssh]
            delete_CkSsh $ssh
            exit
        }

        puts "$cmdOutput"
        set numFinished [expr $numFinished + 1]
    }

}

CkSsh_Disconnect $ssh

delete_CkSsh $ssh