EOF to file on remote host - bash

I need to "cat" a text inside shell script to remote machine via ssh.
This is required for simplicity, so i don't need to keep extra file.
For instance
#!/bin/sh
VAR="some"
VAR1="something"
cat << EOF
apple
green
tree
EOF ---> cat to file.txt on remote machine
do some command
do some command1
exit 0

Try something like this if you're generating file content in runtime:
cat <<EOF | ssh remote 'cat - > /tmp/my_remote_file.txt'
apple
green
tree
EOF
Or simply use scp if file is static.

Just want to note for everyone. Above example works fine for plain text, but if heredoc includes variables then substitution will take place. So important to protect heredoc phrase with single quotes to keep everything intact
For example
cat <<'EOF' | ssh remote 'cat - > /tmp/my_remote_file.txt'
host=$(uname -a)
echo $host
EOF
host variable won't be substituted with actual hostname.
As reference (paragraph 19-7) http://tldp.org/LDP/abs/html/here-docs.html

Related

Using sed command on remote system

I am using the below command on the local machine and it gives me the expected result:
sed -n 's/^fname\(.*\)".*/\1/p' file.txt
When I use the same command(only changed ' to ") to a same file present in the remote system, I do not get any output.
ssh remote-system "sed -n "s/^fname\(.*\)".*/\1/p" file.txt"
Please help me to get this corrected. Thanks for your help.
" and ' are different things in bash, and they are not interchangeable (they're not interchangeable in many languages, however the differences are more subtle) The single quote means 'pretend everything inside here is a string'. The only thing that will be interpreted is the next single quote.
The double quote allows bash to interpret stuff inside
For example,
echo "$TERM"
and
echo '$TERM'
return different things.
(Untested) you should be able to use single quotes and escape the internal single quotes :
ssh remote-system 'sed -n \'s/^fname(.)"./\1/p\' file.txt'
Looks like you can send a single quote with the sequence '"'"' (from this question)
so :
ssh remote-machine 'sed -n '"'"'s/^fname\(.*\)".*/\1/p'"'"' file.txt'
This runs on my machine if I ssh into localhost, there's no output because file.txt is empty, but it's a proof-of-concept.
Or - can you do the ssh session interactively/with a heredoc?
ssh remote-system
[sed command]
exit
or (again untested, look up heredocs for more info)
ssh remote-system <<-EOF
[sed command]
EOF

Combining pipes and here documents in the shell for SSH

Okay, so I've recently discovered the magic of here documents for feeding stdin style lines into interactive commands. However, I'm trying to use this with SSH to execute a bunch of commands on a remote server, but I also need to pipe in some actual input, before executing the extra commands, to confound matters further I also need to get some results back ;)
Here's what I'm trying to use:
#!/bin/sh
RESULT=$(find -type f "$PATH" | gzip | ssh "$HOST" <<- 'REMOTE_SYNC'
cat > "/tmp/.temp_file"
# Do something with /tmp/.temp_file
REMOTE_SYNC
Is this actually correct? Part of the problem I'm having as well is that I need to pipe the data to that file in /tmp, but I should really be generating a randomly named temp file, but I'm not sure how I could do that, assign the name to a variable (so I can get back to it) and still send stdin into it.
I may also extract the find | gzip part to a separate command run locally first, as the gzipped file will likely be small enough that sending it when ready will result in a much shorter SSH connection then sending it as it's generated, but it still doesn't get around the fact that I need to be able to provide both stdin and my extra commands to SSH.
No, you can't do it like this. Both heredoc and the piped input compete for stdin, and only one wins. Look at this example:
echo test | cat << EOF
TEST
EOF
What will this print? test, TEST or both? It prints TEST, so the heredoc wins (at least in bash).
You don't really need this anyway. Luckily ssh takes a command argument, which will be passed on to the shell on the remote host, so you can just use your command as a string here. So something like this:
echo TEST | ssh user#host 'cat > tempfile; cat tempfile; rm tempfile'
would work (althoug it doesn't make much sense), the output of the left side commands is piped through ssh to the remote host and supplied as stdin there.
If you want the data to be compressed when sending it through ssh, you can just enable compression using the -C option.
edit:
Using linebreaks inside a string is perfectly fine, so this works fine too:
echo TEST | ssh user#host '
cat > tempfile
cat tempfile
rm tempfile
'
The only difference to a heredoc would be that you have to escape quotes.
If you use something like echo TEST | ssh user#host "$(<script.sh)" you can write everything into a file...

Why SSH breaks the control flow in Bash

I have following script scanning through a file, each line is hostname of a remote node.
echo -e "node1\nnode2\nnode3" > tempfile
while read aline; do
echo "#$aline";
done < tempfile
this produces #node1 #node2 and #node3 correctly in three lines. But when I add ssh inside the loop, as follows
while read aline; do
echo "#$aline";
ssh $aline 'jps';
done < tempfile
The loop will break after first invocation of ssh and prints only #node1 (without #node2 and `#node3).
I am asking what happened behind the scene (it looks like undefined behaviour)? And how should one realise the same functionality without breaking the while loop.
SSH is doing something with stdin (which is redirected from tempfile) and messing up the reads. Try redirecting stdin.
ssh -n $aline 'jps'
From man ssh:
-n Redirects stdin from /dev/null (actually, prevents reading from stdin).

gnome terminal tabs open multiple ssh connections

I have a file with a list of servers:
SERVERS.TXT:
192.168.0.100
192.168.0.101
192.168.0.102
From a gnome terminal script, I want open a new terminal, with a tab for each server.
Here is what I tried:
gnome-terminal --profile=TabProfile `while read SERVER ; do echo "--tab -e 'ssh usr#$SERVER'"; done < SERVERS.TXT`
Here is the error:
Failed to parse arguments: Argument to "--command/-e" is not a valid command: Text ended before matching quote was found for '. (The text was ''ssh')
Tried removing the space after the -e
gnome-terminal --profile=TabProfile `while read SERVER ; do echo "--tab -e'ssh usr#$SERVER'"; done < SERVERS.TXT`
And I get a similar error:
Failed to parse arguments: Argument to "--command/-e" is not a valid command: Text ended before matching quote was found for '. (The text was 'usr#192.168.0.100'')
Obviously there is a parsing error since the the shell is trying to be helpful by using the spaces to predict and place delimiters. The server file is changed without notice and many different sets of servers need to be looked at.
I found this question while searching for an answer to the issue the OP had, but my issue was a little different. I knew the list of servers, they where not in a file.
Anyway, the other solutions posted did not work for me, but the following script does work, and is what I use to get around the "--command/-e" is not a valid command" error.
The script should be very easy change to suit any need:
#!/bin/sh
# Open a terminal to each of the servers
#
# The list of servers
LIST="server1.info server2.info server3.info server4.info"
cmdssh=`which ssh`
for s in $LIST
do
title=`echo -n "${s}" | sed 's/^\(.\)/\U\1/'`
args="${args} --tab --title=\"$title\" --command=\"${cmdssh} ${s}.com\""
done
tmpfile=`mktemp`
echo "gnome-terminal${args}" > $tmpfile
chmod 744 $tmpfile
. $tmpfile
rm $tmpfile
Now the big question is why does this work when run from a file, but not from within a script. Sure, the issue is about the escaping of the --command part, but everything I tried failed unless exported to a temp file.
I would try something like:
$ while read SERVER;do echo -n "--tab -e 'ssh usr#$SERVER' "; \
done < SERVERS.txt | xargs gnome-terminal --profile=TabProfile
This is to avoid any interpretation that the shell could do of the parameters (anything starting with a dash).
Because it is concatenating strings (using -n), it is necessary to add an space between them.
Is this a problem of parsing command-line options? Sometimes if you have one command sending arguments to another command, the first can get confused. The convention is to use a -- like so:
echo -- "--tab -e 'ssh usr#$SERVER'";
Try to type
eval
before gnome terminal command.
it should be something like this:
eval /usr/bin/gnome-terminal $xargs
worked for me!

BASH script to pass variables without substitution into new script

As part of a system build script I have a script that creates various files and configurations.
However one part of the build script creates a new script that contains variables that I don't want resolved when the build script runs. Code snippet example
cat - > /etc/profile.d/mymotd.sh <<EOF
hostname=`uname -n`
echo -e "Hostname is $hostname"
EOF
I have tried all sorts of combinations of ' and " and ( and [ but I cannot get the script to send the content without substituting the values and placing the substitutes in the new script rather than the original text.
Ideas?
The easiest method, assuming you don't want anything to be substituted in the here doc, is to put the EOF marker in quotes, like this:
cat - > /etc/profile.d/mymotd.sh <<'EOF'
hostname=`uname -n`
echo -e "Hostname is $hostname"
EOF
Easiest is to escape the $
echo -e "Hostname is \$hostname"

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