Bash: how to test stdout of a ping without using any file

Question

I want to retrieve all connected hosts with a script:

for i in {1..9}
do 
    ping -c 1 -w 1 8.8.8.$i | grep ' 0%'
done

So i want to add a condition using if, which would test if the output of each ping (with the piped grep) is empty or not, if it's not empty then host is up.

Cheers

p.s: i would like to avoid the use of a file

score 1 · Answer 1 · answered Apr 19 '16 at 11:46

1

Using the ping return code to determine the status of the machine.

for i in {1..9}
do
    ping_status=$(ping -c 1 8.8.8.$i &> /dev/null && echo success || echo fail)

    if [ $ping_status = success ]
    then echo 'machine is up and running'
    else
       echo 'machine is down'
    fi
done

answered Apr 19 '16 at 11:46

Inian

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I like this answer but are you sure about `&>`? If yes, what does it mean? – derlarsschneider Apr 19 '16 at 11:54
@Inian I tried your code , i get the error: [fail : command not found – aurelien75000 Apr 19 '16 at 11:59
With `&>` I am suppressing all the `stdout` and `stderr` messages to a null handle, since I am worried only about the return code of the `ping` command – Inian Apr 19 '16 at 12:00
@aurelien75000: Works just fine for me! Which shell are you on? – Inian Apr 19 '16 at 12:02

score 1 · Accepted Answer · answered Apr 19 '16 at 11:59

1

Just check the status of the ping command:

for i in {1..9}
do 
    if ping -c 1 -w 1 8.8.8.$i >/dev/null; then 
        echo "$i alive"; 
    else 
        echo "$i dead"
    fi
done

answered Apr 19 '16 at 11:59

oliv

12,690
25
45

score 0 · Answer 3 · edited May 23 '17 at 11:45

0

How to set a variable to the output from a command in Bash?

for i in {1..9}
do
    out="$(ping -c 1 -w 1 8.8.8.$i | grep ' 0%')"
    if [ -z "$out" ]; then
        # output empty
    fi
done

edited May 23 '17 at 11:45

Community

1
1

answered Apr 19 '16 at 11:47

Julien Cassette

11
1

Try `if test -z "$out"; then` instead. – derlarsschneider Apr 19 '16 at 11:52
@aurelien75000 You need a space beetween [ and -z – Julien Cassette Apr 19 '16 at 11:53

score 0 · Answer 4 · answered Apr 19 '16 at 11:55

0

You could use glob matching within a case/esac. This avoids an expensive fork to grep.

for i in {1..9}; do
   case $(ping -c 1 8.8.8.$i) in
   (*" 0%"*)
      echo something
   ;;
   (*)
      echo something else
   ;;
   esac
done

answered Apr 19 '16 at 11:55

Jens

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score 0 · Answer 5 · answered Apr 19 '16 at 12:14

You can do it faster in parallel with GNU Parallel like this:

parallel -j 64 -k 'ip=8.8.8.{}; ping -c 1 -t 1 $ip >/dev/null 2>&1; [ $? -eq 0 ] && echo $ip' ::: {1..254}

Or you can use nmap like this:

nmap -sP 8.8.8.* | tr -d "()" | awk '/Nmap scan report/{h=$NF} /Host is up/{print h}'

Bash: how to test stdout of a ping without using any file

5 Answers5