Bash arguments literal interpretation - bash

Question

I have a simple bash script to run a remote command on a given set of servers.
#!/bin/bash
echo "Command to be run:"
echo "$*"
read nothing
servers="server1 server2 server3"
for server in `echo $servers`
do
echo $server
ssh $server "$*"
echo ""
done
The problem is that the command could contain any number of arguments, hence the use of $* and could also have many different characters including quotes and regular expressions. The basic need here is for the shell to take the arguments, whatever they are, literally so they are passed to the remote server intact without removing quotes or interpreting parenthesis etc.
There are a number of variations I have seen but most deal with a specific character problem or overcomplicate the script or arguments required, and I'm looking to keep at least the arguments free of escape characters etc.
An example with using "#":
./cmd tw_query --no-headings "search Host where name matches '(?i)peter' show summary, nodecount(traverse :::Detail where name matches 'bob')"
Gives:
Command to be run:
tw_query --no-headings search Host where name matches '(?i)peter' show summary, nodecount(traverse :::Detail where name matches 'bob')

Answer 1

You seem to be looking for $#. Say:
ssh $server "$#"
instead. From the manual:
*
Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, it expands to a single word
with the value of each parameter separated by the first character of
the IFS special variable. That is, "$*" is equivalent to "$1c$2c…",
where c is the first character of the value of the IFS variable. If
IFS is unset, the parameters are separated by spaces. If IFS is null,
the parameters are joined without intervening separators.
#
Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, each parameter expands to a
separate word. That is, "$#" is equivalent to "$1" "$2" …. If the
double-quoted expansion occurs within a word, the expansion of the
first parameter is joined with the beginning part of the original
word, and the expansion of the last parameter is joined with the last
part of the original word. When there are no positional parameters,
"$#" and $# expand to nothing (i.e., they are removed).

Answer 2

You actually don't want the arguments passed to the remote server intact, you want them passed to the remote command intact. But that means they need to be wrapped in an extra layer of quotes/escapes/etc so that so that they will come out intact after the remote shell has parsed them.
bash actually has a feature in its printf builtin to add quoting/escaping to a string, but it quotes suitably for interpretation by bash itself -- if the remote shell were something else, it might not understand the quoting mode that it chooses. So in this case I'd recommend a simple-and-dumb quoting style: just add single-quotes around each argument, and replace each single-quote within the argument with '\'' (that'll end the current quoted string, add an escaped (literal) quote, then start another quoted string). It'll look a bit weird, but should decode properly under any POSIX-compliant shell.
Converting to this format is a bit tricky, since bash does inconsistent things with quotes in its search-and-replace patterns. Here's what I came up with:
#!/bin/bash
quotedquote="'\''"
printf -v quotedcommand "'%s' " "${#//\'/$quotedquote}"
echo "Command to be run:"
echo "$quotedcommand"
read nothing
servers="server1 server2 server3"
for server in $servers
do
echo $server
ssh $server "$quotedcommand"
echo ""
done
And here's how it quotes your example command:
'tw_query' '--no-headings' 'search Host where name matches '\''(?i)peter'\'' show summary, nodecount(traverse :::Detail where name matches '\''bob'\'')'
It looks strange to have the command itself quoted, but as long as you aren't trying to use an alias this doesn't cause any actual trouble. There is one significant limitation, though: there's no way to pass shell metacharacters (like > for output redirection) to the remote shell:
./cmd somecommand >outfile # redirect is done on local computer
./cmd somecommand '>outfile' # ">outfile" is passed to somecommand as an argument
If you need to do things like remote redirects, things get a good deal more complicated.

Answer 3

Besides the issue with $* versus $#, if this is for use in a production environment, you might want to consider a tool such as pdsh.
Otherwise, you can try feeding the commands to your script through stdin rather than putting them in argument so you avoid one level of parsing.
#!/bin/bash
read cmd
echo "Command to be run:"
echo $cmd
servers="server1 server2 server3"
for server in `echo $servers` do
echo $server
ssh $server "$cmd"
echo ""
done
and use it like this
$ ./cmd <<'EOT'
> tw_query --no-headings "search Host where name matches '(?i)peter' show summary, nodecount(traverse :::Detail where name matches 'bob')"
> EOT
Command to be run:
tw_query --no-headings "search Host where name matches '(?i)peter' show summary, nodecount(traverse :::Detail where name matches 'bob')"
Maybe a little far-fetched, but it could work.