Bash script variable not being passed via ssh

Question

I have a bash script which ssh's to a server, and depending on the status of a variable performs a task:

#!/bin/bash

foo=$1
ssh [email protected] '
echo In host
if [ "$foo" == "yes" ]; then
   echo "Foo!"
fi
'

When I run sh script.sh yes, although the ssh command works, the conditional evaluates to false. I can see this if I echo $foo - it prints an empty line. How can I access the value of foo within the ssh command?

choroba · Accepted Answer · 2019-07-04 10:48:57Z

1

Variables aren't transferred to a remote machine. You can expand the variable in the code sent through ssh, but you have to be extremely careful because it opens the door to uncontrolled code execution:

#!/bin/bash

foo=$1
ssh [email protected] '
echo In host
if [ "'"$foo"'" == "yes" ]; then
   echo "Foo!"
fi
'

Now imagine (don't try) what happens if foo='$(rm -rf /)'.

answered Jul 4, 2019 at 10:48

choroba

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