Using Variables inside one another Bash

Question

I am running a for loop that calls in a variable from another file:

hostnames.txt

The variables in that file look like this:

export HOSTNAME_0=<hostname>
export HOSTNAME_1=<hostname>
export HOSTNAME_2=<hostname>

I am trying use them inside a for loop like this:

. hostnames.txt
for f in {0..10}; do
ssh $HOSTNAME_'{$f}'
if [$? !=0]; then
   echo "Unable to SSH to server $HOSTNAME_'{$f}'"
   exit 1
fi

However its not reading the value correctly, and I'm not sure what I'm missing. Would love any help.

Check your spacing inside the [ ], or maybe use (( ))

cdarke
– cdarke

2017-04-14 15:25:20 +00:00
Commented Apr 14, 2017 at 15:25 — cdarke
– cdarke, Commented Apr 14, 2017 at 15:25

vdavid · Accepted Answer · 2017-04-14 16:43:25Z

3

You need to build your variable name and access it with ${!var}, e.g.:

. hostnames.txt
for f in {0..10}; do
  hostnamevar=HOSTNAME_${f}
  ssh ${!hostnamevar}
  if [ $? -ne 0 ]; then
    echo "Unable to SSH to server ${!hostnamevar}"
    exit 1
  fi
done

edited Apr 14, 2017 at 16:43

answered Apr 14, 2017 at 14:37

vdavid

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4 Comments

Gordon Davisson Over a year ago

You need spaces in the if test expression: if [ $? != 0 ]; then.

vdavid Over a year ago

@GordonDavisson I was merely copying his code which wasn’t relevant IMO. Anyways I’ve edited the answer so as to fix the rest of his code too.

user2019182 Over a year ago

Thanks that worked. I have an additional question though, I have additional commands I want to execute on the remote server after I've logged in and now none of them are running. Any idea how do actually get them to run?

vdavid Over a year ago

@user2019182 Since this looks like a different issue, please open another thread.

Walter A · Accepted Answer · 2017-04-15 09:29:17Z

1

When you don't have other vars starting with "HOSTNAME", you can use

    . hostnames.txt
    for host in $(set | sed -n '/^HOSTNAME*=/ s/[^=]*=//p') ; do
       ssh "${host}"
       # or, for calling 2 commands:
       # ssh "${host}" "echo 1 2 3; echo 4"
       if [ $? -ne 0 ]; then
          echo "Unable to SSH to server ${host}"
          exit 1
       fi
    done

edited Apr 15, 2017 at 9:29

answered Apr 14, 2017 at 21:53

Walter A

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