I want to run a remote command over ssh. So, the one line command is
ssh [email protected] 'VMID=`./run_prog` && if [ -n $VMID ]; then echo "id=$VMID"; vim-cmd vmsvc/power.off $VMID; else echo "$VMID empty"; fi'
Problem is that if VMID is empty or non-empty, I see the output of vim-cmd.
id=
Usage: power.off vmid
or
34
Powering off VM:
How can I be sure that vim-cmd is executed for non-empty VMID values?
The problem is that you do not quote the variable inside the if condition. You have to do it this way:
if [ -n "$VMID" ]
You might wonder why if you don't quote you face problems. Well the answer is in man test:
-n STRING
the length of STRING is nonzero
STRING
equivalent to -n STRING
So when VMID is empty, the if condition results like this:
if [ -n ]
and test will assume that you want to check if -n is an empty string. It won't undestand that you have used -n as an option. So, -n is not empty and the test passes.
If you use quotation, test will understand what you want.
If I can add a suggestion, don't use backquotes for command substitution. Use $(./run_prog) instead. Check this answer if you want more information about it.
VMID emptyto be output? Would the lack of any other output be sufficient to indicate that it was empty?run_proghave a non-zero exit status if it fails to produce any output? You could test that instead of explicitly checking the contents of the variable.VMID=$(./run_prog) && vim-cmd vmsvc/power.off "$VIMD".