Assigning variables inside remote shell script execution over SSH

Question

I am trying to execute some shell script on a remote server via SSH.

Given below is a code sample:

ssh -i $KEYFILE_PATH ubuntu@$TARGET_INSTANCE_IP "bash"  << EOF
#!/bin/bash
cat /home/ubuntu/temp.txt
string=$(cat /home/ubuntu/temp.txt )
echo $string
EOF

cat prints the expected result but $string prints nothing.

How do I store the return value of cat in a variable?

score 1 · Accepted Answer · answered Jul 03 '16 at 08:21

1

You need to make the content of Here doc literal otherwise they will be expanded in the current shell, not in the desired remote shell.

Quote EOF:

ssh .... <<'EOF'
...
...
EOF

answered Jul 03 '16 at 08:21

heemayl

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tried that out !! no luck !! – Silent_Rebel Jul 03 '16 at 08:25
@Silent_Rebel Where is `/home/ubuntu/temp.txt` file located? Local or remote? – heemayl Jul 03 '16 at 08:29
its there on the remote server.. – Silent_Rebel Jul 03 '16 at 08:33
1

I think that was the tweak.. It is working now .. thanks.. – Silent_Rebel Jul 03 '16 at 09:04

score 1 · Answer 2 · answered Jul 03 '16 at 08:53

You should be able to simply do this:

ssh -i $KEYFILE_PATH ubuntu@$TARGET_INSTANCE_IP "bash"  <<'_END_'
    cat /home/ubuntu/temp.txt
    string=$(cat /home/ubuntu/temp.txt)
    echo $string
_END_

<<'_END_' ... _END_ is called a Here Document literal, or "heredoc" literal. The single quotes around '_END_' prevent the local shell from interpreting variables and commands inside the heredoc.

score 0 · Answer 3 · answered Jul 03 '16 at 09:22

The intermediate shell is not required (assuming you use bash on the remote system). Also you dont have to use an intermediate HERE-DOC. Just pass a multiline Command:

ssh -i $KEYFILE_PATH ubuntu@$TARGET_INSTANCE_IP '

cat /home/ubuntu/temp.txt
string=$(cat /home/ubuntu/temp.txt )
echo $string
'

Note I am using single quotes to prevent evaluation on the local shell.

Assigning variables inside remote shell script execution over SSH

3 Answers3