如何在bash脚本中将该命令的结果存储为变量？

Question

I'm building a simple tool that will let me know if a site "siim.ml" resolves. If I run the command "ping siim.ml | grep "Name or service not known"" in the linux command line then it only returns text if the site does not resolve. Any working site returns nothing.

Using this I want to check if the result of that command is empty, and if it is I want to perform an action.

Problem is no matter what I do the variable is empty! And it still just prints the result to stdout instead of storing it.

I've already tried switching between `command` and $(command), and removed the pipe w/ the grep, but it has not worked

#!/bin/bash

result=$(ping siim.ml | grep "Name or service not known")

echo "Result var = " $result

if ["$result" = ""]
then
        #siim.ml resolved
        #/usr/local/bin/textMe/testSite.sh "siim.ml has resolved"
        echo "It would send the text"
fi

When I run the script it prints this:

ping: siim.ml: Name or service not known
Result var =
It would send the text

Answer 1

It's almost certainly because that error is going to standard error rather than standard output (the latter which will be captured by $() ).

You can combine standard error into the output stream as follows:

result=$(ping siim.ml 2>&1 | grep "Name or service not known")

In addition, you need spaces separating the [ and ] characters from the expression:

if [ "$result" = "" ]

Answer 2

Or even slightly more terse, just check whether ping succeeds, eg

if ping -q -c 1 siim.ml &>/dev/null
then
    echo "It would send the text"
    ## set result or whatever else you need on success here
fi

This produces no output due to the redirection to /dev/null and succeeds only if a successful ping of siim.ml succeeds.