CODEWITHSUNDEEP
bash
tlre0952b
tlre0952b

Reputation: 751

IF statement condition command

In bash I want to test if there is a DNS entry for a hostname. If there is then I want to do X otherwise do Y.

How can I write this? So far I am thinking the following:

if [[ `ping -c 1 $1 2> /dev/null` ]]; then
   # the hostname was not found
   # perform Y
else
   # the hostname was found
   # perform X
fi;

After writing this I am not certain of whether to use &2> instead of 2>. With different exit codes it might be better for me to just do X when the exit code of the ping command is 0.

How would I put this?

Upvotes: 0

Views: 86

Answers (1)

jwodder
jwodder

Reputation: 57470

It should be 2>, not &2>. However, [[ `foo` ]] will capture the output of the command foo and try to evaluate it as a conditional expression. This is not what you want. In order to run a command and test its exit status, just do:

if ping -c 1 "$1" 2> /dev/null; then
   # the hostname was found
   # perform X
else
   # the hostname was not found
   # perform Y
fi

(It's a good idea to put $1 in quotes in case the variable contains any special characters.)

Note that an if test in bash succeeds on an exit status of 0, so you need to swap the Y and X blocks.

If you want to suppress all output from ping, then redirect its stdout as well:

if ping -c 1 "$1" 1>/dev/null 2>/dev/null; then
# ...

Upvotes: 4

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