To test whether the output is terminal we can do -t STDOUT:
if (-t STDOUT) {
# print with terminal control chars
} else {
# just plain print
}
But when the script is executed in the ssh session not run from terminal (Jenkins in my case), the -t test still returns true and my output gets polluted with control chars:
ssh user#server "/my/script.pl"
Why does the -t detects the terminal?
I don't know why ssh is allocating a terminal for you — mine defaults to not doing that even if the output of ssh goes to a terminal — but passing -T to ssh will disable pseudo-tty creation on the remote end.
$ ssh -t localhost "perl -E'say -t STDOUT ?1:0'"
1
Connection to localhost closed.
$ ssh -T localhost "perl -E'say -t STDOUT ?1:0'"
0
From ssh's man page:
-T Disable pseudo-tty allocation.
-t Force pseudo-tty allocation. This can be used to execute arbitrary
screen-based programs on a remote machine, which can be very useful,
e.g. when implementing menu services. Multiple -t options force tty
allocation, even if ssh has no local tty.
Perhaps it would be better if you instead forced ssh to allocate a pty —
From the ssh manual:
-t Force pseudo-tty allocation. This can be used to execute arbitrary screen-based programs
on a remote machine, which can be very useful, e.g. when implementing menu services.
Multiple -t options force tty allocation, even if ssh has no local tty.
The longer answer: -t (the Perl or Bourne shell function) reliably detects whether the stream is a “typewriter,” but ssh will normally only allocate a pseudo-teletype (pty) stream in interactive shells, not when other programs are being started.
See also RequestTTY as an option in .ssh/config.
Related
I planed to starting emacs from the the start.sh as
$ head start.sh
#! /bin/bash
{
#starting emacs servers
emacs --daemon=orging
emacs --daemon=coding
#waiting...
#invoke emacsclients
emacsclient -c -s "orging" &
emacsclient -c -s "coding" &
......
} &> /dev/null
Two clients run respectively under servers of orging and coding.
A problem occurred to this situation is that the invoked running clients are not labelled with appropriate server names.
So a manual steps of testing might be need to determine who is who.
As an alternative, the servers could be scheduled with one running at the top , the other at the end after starting from in the start.sh,
How could determine which server a client attached in a straightforward way on a working frame?
You can inspect the variable server-name - interactively with C-h v server-name RET.
On RHEL, the below command works:
psql -h hostname -U username -p port_no -d database -f /tmp/myfile.sql &> logfile01.txt
On FreeBSD, this throws error:
"Invalid null command"
Please suggest.
If you use this only on the command line then there is no need to change the shell.
To redirect stdout and stderr to a file in C-Shell synthax simply use ">& filename".
Different story is, if you want to write shell scripts. Bourne Shell and it's clones (like i.e. Bash) are better suited for writing script. See this Unix FAQ "Csh Programming Considered Harmful": http://www.faqs.org/faqs/unix-faq/shell/csh-whynot/
This redirection works in bash
&> logfile01.txt
, but it does not work in csh which is the default shell in FreeBSD.
# set | grep shell
shell /bin/csh
# ls -la &> logfile01.txt
Invalid null command.
Bash is not installed by default. You can install it
pkg install bash
and configure it as the default shell.
My perl code does this
#!/usr/bin/perl
sleep 2;
exec 'ssh', '-o', "ConnectTimeout=10", "newhost", "sleep 3;pwd";
the problem is when sleep is executing what ever I type on the terminal (during execution)
disappears to non interactive shell in newhost.
eg:
user#a02$perl test.pl
ls
user#a02$ #ls is not executed
command ls executes if I don't use exec or system.
Is there a way to execute the contents of the buffer?
After a bit of digging i found ssh has has an stdio redirector when used with -n option.
http://www.pixelbeat.org/programming/stdio_buffering/
To tell ssh that the remote command doesn't require any input use the -n option
I am trying to get the output of a command in a variable and checking whether its matching with other variable.
$login1=`ssh ****************** date`;
This command when typed manually will expect a prompt " Password: " . When i run it from the script it is ruuning that command and printing that prompt waiting for user to enter, but i dont need that. I just need to get that output and compare
if($login1=~ /Password:/)
{
print " yes";
}
else
{
print "No ";
}
However the script is just stopping at Password prompt . Please suggest me on how to achieve this .
You might want to look at the -f flag for ssh:
-f Requests ssh to go to background just before command execution.
This is useful if ssh is going to ask for passwords or
passphrases, but the user wants it in the background. This
implies -n. The recommended way to start X11 programs at a
remote site is with something like ssh -f host xterm.
If you want to avoid passwords, set up a public/private key pair with no passphrase (dangerous, but much less dangerous than putting a password in a script) and copy the public key to the remote site. IIRC, it goes something like this:
localhost $ ssh-keygen -b 2048 -t ecdsa -N '' -f ./datekey
localhost $ scp ./datekey.pub remotehost:/tmp
localhost $ ssh remotehost
(login)
remotehost $ cat /tmp/datekey.pub >> ~/.ssh/authorized_keys
remotehost $ logout
localhost $ ssh -i ./datekey remotehost date
Make sure you store ./datekey somewhere no other user can access it at all -- not even read access.
If you're just trying to detect, you might simply need to feed it EOF to get it to move along:
$login1=`ssh ****************** date < /dev/null`;
I am trying to find a good way to tail a file on a remote host. This is on an internal network of Linux machines. The requirements are:
Must be well behaved (no extra process laying around, or continuing output)
Cannot require someone's pet Perl module.
Can be invoked through Perl.
If possible, doesn't require a custom built script or utility on the remote machine (regular linux utilities are fine)
The solutions I have tried are generally of this sort
ssh remotemachine -f <some command>
"some command" has been:
tail -f logfile
Basic tail doesn't work because the remote process continues to write output to the terminal after the local ssh process dies.
$socket = IO:Socket::INET->new(...);
$pid = fork();
if(!$pid)
{
exec("ssh $host -f '<script which connects to socket and writes>'");
exit;
}
$client = $socket->accept;
while(<$client>)
{
print $_;
}
This works better because there is no output to the screen after the local process exits but the remote process doesn't figure out that its socket is down and it lives on indefinitely.
Have you tried
ssh -t remotemachine <some command>
-t option from the ssh man page:
-t Force pseudo-tty allocation. This can be used to execute
arbitrary screen-based programs on a remote machine, which
can be very useful, e.g. when implementing menu services.
Multiple -t options force tty allocation, even if ssh has no local tty.
instead of
-f Requests ssh to go to background just before command execution.
This is useful if ssh is going to ask for passwords or passphrases,
but the user wants it in the background.
This implies -n. The recommended way to start X11 programs at a remote
site is with something like ssh -f host xterm.
Some ideas:
You could mount it over NFS or CIFS, and then use File::Tail.
You could use one of Perl's SSH modules (there are a number of them), combined with tail -f.
You could try Survlog Its OS X only though.
netcat should do it for you.
You can Tail files remotely using bash and rsync. The following script is taken from this tutorial: Tail files remotely using bash and rsync
#!/bin/bash
#Code Snippet from and copyright by sshadmincontrol.com
#You may use this code freely as long as you keep this notice.
PIDHOME=/a_place/to/store/flag/file
FILE=`echo ${0} | sed 's:.*/::'`
RUNFILEFLAG=${PIDHOME}/${FILE}.running
if [ -e $RUNFILEFLAG ]; then
echo "Already running ${RUNFILEFLAG}"
exit 1
else
touch ${RUNFILEFLAG}
fi
hostname=$1 #host name to remotlely access
log_dir=$2 #log directory on the remotehost
log_file=$3 #remote log file name
username=$3 #username to use to access remote host
log_base=$4 #where to save the log locally
ORIGLOG="$log_base/$hostname/${log_file}.orig"
INTERLOG="$log_base/$hostname/${log_file}.inter"
FINALLOG="$log_base/$hostname/${log_file}.log"
rsync -q -e ssh $username#$hostname:$log_dir/$log_file ${ORIGLOG}
grep -Ev ".ico|.jpg|.gif|.png|.css" > ${INTERLOG}
if [ ! -e $FINALLOG ]; then
cp ${INTERLOG} ${FINALLOG}
else
LINE=`tail -1 ${FINALLOG}`
grep -F "$LINE" -A 999999999 ${INTERLOG} \
| grep -Fv "$LINE" >> ${FINALLOG}
fi
rm ${RUNFILEFLAG}
exit 0
rsync://[USER#]HOST[:PORT]/SRC... [DEST] | tail [DEST] ?
Someone suggested using nc (netcat). This solution does work but is less ideal than just using ssh -t. The biggest problem is that you have to use nc on both sides of the connection and need to do some port discovery on the local machine to find a suitable port over which to connect. Here is the adaptation of the above code to use netcat:
$pid = fork();
if(!$pid)
{
exec("ssh $host -f 'tail -f $filename |nc $localhost $port'");
exit;
}
exec("nc -l -p $port");
There is File::Tail. Don't know if it helps?