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Full Discussion: SSH sessions from bash script
Top Forums Shell Programming and Scripting SSH sessions from bash script Post 302307130 by qneill on Tuesday 14th of April 2009 04:40:39 PM
Old 04-14-2009
No reason you have to use a "here script" with <<EOF, you can pipe commands directly to the standard input of ssh, for example using echo:

Code:
$ D=/tmp; F1=x1; echo "F2=$D/$F1
echo on \$(hostname): escaped: D=\$D F1=\$F1 F2=\$F2
echo on \$(hostname): not escaped: D=$D F1=$F1 F2=$F2
df $D >\$F2; ls -l \$F2; cat \$F2; rm -rf \$F2; ls -l \$F2
" | ssh qneill@qneill-linux

this shows a couple of local variables D and F1 (expanded locally when the local echo is executed), and a remote variable F2 (expands to nothing locally, but remotely expands to the assigned value). The commands produce this output:

Code:
on qneill-linux: escaped: D= F1= F2=/tmp/x1
on qneill-linux: not escaped: D=/tmp F1=x1 F2=
-rw-r--r-- 1 qneill 30101 125 2009-04-14 15:25 /tmp/x1
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/hda1            147581948  78980980  61104240  57% /
ls: /tmp/x1: No such file or directory

The commands shown use the local variable D and remote variable F2, creating, using, and removing a file (/tmp/x1 on the remote machine).

If all of your variable expansions are constant, or only depend on remote things, you can use single quotes and avoid having to escape all the $ signs:

Code:
echo 'D=/tmp; F1=x1; F2=$D/$F1
echo on $(hostname): D=$D F1=$F1 F2=$F2
df $D >$F2; ls -l $F2; cat $F2; rm -rf $F2; ls -l $F2
' | ssh qneill@qneill-linux

which yields
Code:
on qneill-linux: D=/tmp F1=x1 F2=/tmp/x1
-rw-r--r-- 1 qneill 30101 125 2009-04-14 15:34 /tmp/x1
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/hda1            147581948  78980960  61104260  57% /
ls: /tmp/x1: No such file or directory

Once you start using this mechanism for anything complicated, you will quickly run into many quoting issues. Consider writing a script that generates code on the remote system, or a templated script that can be parameterized locally or remotely as needed, then executed remotely with a single call to ssh.
--
qneill
 

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LEARN ABOUT FREEBSD

ddb

DDB(8)							    BSD System Manager's Manual 						    DDB(8)

NAME

     ddb -- configure DDB kernel debugger properties

SYNOPSIS

     ddb capture [-M -core] [-N -system] print
     ddb capture [-M -core] [-N -system] status
     ddb script scriptname
     ddb script scriptname=script
     ddb scripts
     ddb unscript scriptname
     ddb pathname

DESCRIPTION

     The ddb utility configures certain aspects of the ddb(4) kernel debugger from user space that are not configured at compile-time or easily
     via sysctl(8) MIB entries.

     To ease configuration, commands can be put in a file which is processed using ddb as shown in the last synopsis line.  An absolute pathname
     must be used.  The file will be read line by line and applied as arguments to the ddb utility.  Whitespace at the beginning of lines will be
     ignored as will lines where the first non-whitespace character is '#'.

OUTPUT CAPTURE

     The ddb utility can be used to extract the contents of the ddb(4) output capture buffer of the current live kernel, or from the crash dump of
     a kernel on disk.	The following debugger commands are available from the command line:

     capture [-M core] [-N system] print
	     Print the current contents of the ddb(4) output capture buffer.

     capture [-M core] [-N system] status
	     Print the current status of the ddb(4) output capture buffer.

SCRIPTING

     The ddb utility can be used to configure aspects of ddb(4) scripting from user space; scripting support is described in more detail in
     ddb(4).  Each of the debugger commands is available from the command line:

     script scriptname
	     Print the script named scriptname.

     script scriptname=script
	     Define a script named scriptname.	As many scripts contain characters interpreted in special ways by the shell, it is advisable to
	     enclose script in quotes.

     scripts
	     List currently defined scripts.

     unscript scriptname
	     Delete the script named scriptname.

EXIT STATUS

     The ddb utility exits 0 on success, and >0 if an error occurs.

EXAMPLES

     The following example defines a script that will execute when the kernel debugger is entered as a result of a break signal:

	   ddb script kdb.enter.break="show pcpu; bt"

     The following example will delete the script:

	   ddb unscript kdb.enter.break

     For further examples, see the ddb(4) and textdump(4) manual pages.

SEE ALSO

     ddb(4), textdump(4), sysctl(8)

HISTORY

     The ddb utility first appeared in FreeBSD 7.1.

AUTHORS

     Robert N M Watson

BUGS

     Ideally, ddb would not exist, as all pertinent aspects of ddb(4) could be configured directly via sysctl(8).

BSD
								 December 24, 2008							       BSD
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