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nested escape chars in a shell command

P: n/a
I'm try run an ssh command in pexpect and I'm having trouble getting
everything escaped to do what i want.

Here's a striped down script showing what i want to do.

--
#!/usr/bin/env python
import pexpect
import sys
if len(sys.argv) < 3:
print "ssh.py host command"
sys.exit(1)

host = sys.argv[1]
command = sys.argv[2]

child = pexpect.spawn('''sh -x -c "stty -echo ; ssh -t -o
'StrictHostKeyChecking no' %s '%s' |awk '{print \"%s:\"$0}' "
'''%(host,command,host), timeout=30)

child.setlog(sys.stdout)
child.expect(pexpect.EOF)
--

The problem in the pexpect.spawn line, It doesn't like the \"%s:\" part
of the awk command. This is necessary so i can see what server the
command is running on, In the full script the command will be running
on about 100 servers at a time.
It parses out into:
+ stty -echo
+ ssh -t -o 'StrictHostKeyChecking no' testserver date
+ awk '{print testserver:$0}'
It totally strips out the "

The stty -echo is required because part of what the program does is it
tries to remember any passwords that are asked for, So you can run a
command like "su -c id" and it will remember roots password for the
next
server and try that. -echo keeps the root password from being echoed to
the screen.

The second problem with the command is while "su -c id" works (taking
out the awk part) running any command with more then one word after the
-c in su fails, It strips out the '
like so:
../sshexpect testserver "su -c 'ls -l /root'"
+ stty -echo
+ ssh -t -o 'StrictHostKeyChecking no' testserver 'su -c ls' -l /root
su: user /root does not exist

I have tried every combination of escaping i can think of can i can't
get either problem solved.

Any ideas?

Eli

Oct 18 '05 #1
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3 Replies


P: n/a
Eli Criffield wrote:
I'm try run an ssh command in pexpect and I'm having trouble getting
everything escaped to do what i want.

Here's a striped down script showing what i want to do.

--
#!/usr/bin/env python
import pexpect
import sys
if len(sys.argv) < 3:
print "ssh.py host command"
sys.exit(1)

host = sys.argv[1]
command = sys.argv[2]

child = pexpect.spawn('''sh -x -c "stty -echo ; ssh -t -o
'StrictHostKeyChecking no' %s '%s' |awk '{print \"%s:\"$0}' "
'''%(host,command,host), timeout=30)

child.setlog(sys.stdout)
child.expect(pexpect.EOF)
--

The problem in the pexpect.spawn line, It doesn't like the \"%s:\" part
of the awk command. This is necessary so i can see what server the
command is running on, In the full script the command will be running
on about 100 servers at a time.
It parses out into:
+ stty -echo
+ ssh -t -o 'StrictHostKeyChecking no' testserver date
+ awk '{print testserver:$0}'
It totally strips out the "

The stty -echo is required because part of what the program does is it
tries to remember any passwords that are asked for, So you can run a
command like "su -c id" and it will remember roots password for the
next
server and try that. -echo keeps the root password from being echoed to
the screen.

The second problem with the command is while "su -c id" works (taking
out the awk part) running any command with more then one word after the
-c in su fails, It strips out the '
like so:
./sshexpect testserver "su -c 'ls -l /root'"
+ stty -echo
+ ssh -t -o 'StrictHostKeyChecking no' testserver 'su -c ls' -l /root
su: user /root does not exist

I have tried every combination of escaping i can think of can i can't
get either problem solved.

Any ideas?

Eli


You can pass the argument list of your command to
pexpect.spawn(comm, args=['arg1','arg2'])
If the argument list is empty, pexpect tries to get the arguments
from the comm you passed to it. I guess this gives you problems.

Try using the args parameter.
Simplest would be args=[' '] just to avoid the processing.
Oct 19 '05 #2

P: n/a
I can't seem to get that to work either.

child =
pexpect.spawn('/bin/sh',args=['-c','/usr/bin/ssh','-t','-o','StrictHostKeyChecking
no',host,command,'|','awk','{print %s:$0}'%host], timeout=30)

Complains its getting the wrong arguments to ssh.

Eli

Oct 20 '05 #3

P: n/a
I think you're mistaken about how 'sh -c' works. The next argument after "-c" is
the script, and following arguments are the positional arguments. (what, you've
never used -c in conjunction with positional arguments? me either!)

Example:
------------------------------------------------------------------------
$ /bin/sh -c 'echo $#' a b c

# i.e., a blank line
$ /bin/sh -c 'echo $# 0=$0 1=$1 2=$2' a b c
2 0=a 1=b 2=c
# i.e., a, b, c went to positional arguments
------------------------------------------------------------------------

Additionally, unless pexpect.spawn behaves differently than os.spawnv,
"-c" is actually going to /bin/sh's argv[0], and you end up trying to execute
/usr/bin/ssh as a shell script, which is probably not what you want!

------------------------------------------------------------------------
def shellquote(arg):
# shell quoting technique I first read about on the 'git' development list
# Everything is safely quoted inside a ''-quoted string, except a ' itself,
# which can be written as '\'' (a backslash-escaped ' outside of the ''-quoted
# string)
return "'" + arg.replace("'", "'\\''") + "'"

def shellquotelist(args):
return " ".join([shellquote(arg) for arg in args])

# XXX: you may wish to assemle 'command' using shellquotelist too
command1 = shellquotelist(['/bin/sh', '-c','/usr/bin/ssh','-t','-o',
'StrictHostKeyChecking no',host,command])
command2 = shellquotelist(['awk','{print %s:$0}'%host])

child = \
pexpect.spawn('/bin/sh',
args=['/bin/sh', '-c', command1 + "|" + command2],
timeout=30)
------------------------------------------------------------------------

Finally, in your case the use of awk would seem to be gratuitous. Instead,
prepend the hostname to each line when you read the lines in. (this could easy
or hard depending on the structure of the code where you read the output
generated by child---if you do it with readline() or by iterating over the file,
it is probably easy)

Jeff

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Oct 21 '05 #4

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