CkPython

Receive from an SSH Channel Until Any Pattern Matches

Demonstrates the Chilkat Ssh.ChannelReceiveUntilMatchN method, which works like ChannelReceiveUntilMatch but returns when any pattern in a StringArray matches. The arguments are the channel number, the pattern array, the charset, and case sensitivity. The array must contain at least one element.

Important: Set the ReadTimeoutMs property before calling this method. It defaults to 0, meaning no limit, so without it the call waits forever if the received data never contains a match.

Background: A command often has more than one possible outcome, and your code should react to whichever occurs rather than hang waiting for one specific string. A common non-interactive pattern is to have the command print one marker on success and a different marker on failure, then match on the set. (With no PTY there is no shell prompt to match against, so markers you emit yourself are the dependable signal.) The first matching content in the stream wins; array order does not override an earlier token. Empty elements are ignored and duplicates are allowed.

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import sys
import chilkat

success = False

#  Demonstrates the Ssh.ChannelReceiveUntilMatchN method, which receives text until ANY pattern
#  in a StringArray is matched.  The 1st argument is the channel number, the 2nd is the array of
#  patterns, the 3rd is the charset, and the 4th selects case-sensitive matching.

ssh = chilkat.CkSsh()

sshPort = 22
success = ssh.Connect("ssh.example.com",sshPort)
if (success == False):
    print(ssh.lastErrorText())
    sys.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.
password = "mySshPassword"

success = ssh.AuthenticatePw("mySshLogin",password)
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

channelNum = ssh.OpenSessionChannel()
if (channelNum < 0):
    print(ssh.lastErrorText())
    sys.exit()

#  Start a shell WITHOUT requesting a PTY.  Without a PTY the shell sees it is connected to a
#  raw data pipe and enters non-interactive mode: it suppresses the command prompt, does not
#  echo typed commands back, and skips interactive login scripts.  The output is therefore
#  clean and easily parseable -- but because no prompt is ever sent, code must not wait for
#  one.  Instead, have each command print a predictable marker, or wait for EOF / channel close.
success = ssh.SendReqShell(channelNum)
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

#  There is no prompt to match on.  Instead, run a command that prints one marker on success
#  and a different marker on failure, then wait for whichever appears first.
success = ssh.ChannelSendString(channelNum,"test -f /etc/hosts && echo OK_MARKER || echo ERR_MARKER\n","utf-8")
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

patterns = chilkat.CkStringArray()
patterns.Append("OK_MARKER")
patterns.Append("ERR_MARKER")

#  IMPORTANT: Set a read timeout before receiving until a match.  ReadTimeoutMs defaults to 0,
#  which means no limit -- without it, this call waits forever if the received data never
#  contains a match.
ssh.put_ReadTimeoutMs(15000)

caseSensitive = False
success = ssh.ChannelReceiveUntilMatchN(channelNum,patterns,"utf-8",caseSensitive)
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

output = ssh.getReceivedText(channelNum,"utf-8")
if (ssh.get_LastMethodSuccess() == False):
    print(ssh.lastErrorText())
    sys.exit()

print(output)

ssh.Disconnect()