Perl

Receive from an SSH Channel Until a Pattern Matches

Demonstrates the Chilkat Ssh.ChannelReceiveUntilMatch method, which receives text until the accumulated text matches a pattern. The arguments are the channel number, the pattern, the charset, and whether matching is case-sensitive. Existing buffered text is checked before waiting for more network data.

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: Driving a shell channel means knowing when the remote side has finished talking. With no PTY requested the shell is non-interactive and never prints a prompt, so the reliable signal is a marker you deliberately echo after your command. This method automates "read until you see X." The pattern syntax is deliberately minimal: literal characters plus *, which matches zero or more characters and can span line breaks. ? and bracket classes are not supported, and backslash does not escape a literal *.

Chilkat Perl Downloads

Download Chilkat for Perl

Chilkat2 Perl

use strict;
use warnings;
use Chilkat2;

# Demonstrates the Ssh.ChannelReceiveUntilMatch method, which receives text until the
# accumulated text matches a pattern.  The 1st argument is the channel number, the 2nd is the
# pattern, the 3rd is the charset, and the 4th selects case-sensitive matching.  The pattern
# supports literal characters plus "*", which matches zero or more characters.

my $ssh = Chilkat2::Ssh->new;

my $sshPort = 22;
my $success = $ssh->Connect('ssh.example.com', $sshPort);
if (!$success) {
    print $ssh->LastErrorText, "\n";
    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.
my $password = 'mySshPassword';

$success = $ssh->AuthenticatePw('mySshLogin', $password);
if (!$success) {
    print $ssh->LastErrorText, "\n";
    exit;
}

my $channelNum = $ssh->OpenSessionChannel();
if ($channelNum < 0) {
    print $ssh->LastErrorText, "\n";
    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) {
    print $ssh->LastErrorText, "\n";
    exit;
}

# There is no prompt to wait for, so make the command itself announce when it has finished
# by echoing a marker after it.
$success = $ssh->ChannelSendString($channelNum, "ls -l /tmp; echo DONE_MARKER\n", 'utf-8');
if (!$success) {
    print $ssh->LastErrorText, "\n";
    exit;
}

# 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->ReadTimeoutMs(15000);

# Receive until the marker appears in the output.
my $caseSensitive = 0;
$success = $ssh->ChannelReceiveUntilMatch($channelNum, 'DONE_MARKER', 'utf-8', $caseSensitive);
if (!$success) {
    print $ssh->LastErrorText, "\n";
    exit;
}

my $output = $ssh->GetReceivedText($channelNum, 'utf-8');
if (!$ssh->LastMethodSuccess) {
    print $ssh->LastErrorText, "\n";
    exit;
}

print $output, "\n";

$ssh->Disconnect();