get hostname from string using bash script

Question

In my bash script I need to extract all hostnames from output of command for further ping:

for host in `echo $MXrecords | awk '{ printf "%s", $0; }'` ; do
    ping -c1 $host 2> /dev/null > /dev/null
    if [ "$?" -eq "0" ] ; then
        answ="OK"
    else
        answ="BAD"
    fi

    echo "\t$host [$answ]" 
done

But I have some extra string:

40 [BAD]
alt2.aspmx.l.google.com. [OK]
30 [BAD]
alt3.aspmx.l.google.com. [OK]

I get var MXrecords by means of dig:

MXrecords=`dig @$DNSserver $domainName IN MX +short +multiline | awk '{ printf "\t%s\n", $0; }'`

It would be useful if you showed us what is the value in $MXrecords — Tuxdude
– Tuxdude, Commented Mar 18, 2013 at 19:22

Ansgar Wiechers · Accepted Answer · 2013-03-18 19:27:22Z

1

From the output it looks like $MXrecords contains the MX records including their priority:

40 alt2.aspmx.l.google.com.
30 alt3.aspmx.l.google.com.

Try replacing this:

`echo $MXrecords | awk '{ printf "%s", $0; }'`

with this:

$(echo "$MXrecords" | awk '{print $2}')

answered Mar 18, 2013 at 19:27

Ansgar Wiechers

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Comments

Ansgar Wiechers · Accepted Answer · 2013-03-18 19:43:13Z

0

Try this instead :

for host in ${MXrecords##* }; do
    if ping -c1 $host &>/dev/null; then
        answ="OK"
    else
        answ="BAD"
    fi

    echo "\t$host [$answ]" 
done

Note

${MXrecords##* } is a parameter expansion bash trick (a buil-tin)
&>/dev/null is a bash shorthand for >/dev/null 2>&1
The backquote (`) is used in the old-style command substitution. The foo=$(command) syntax is recommended instead. Backslash handling inside $() is less surprising, and $() is easier to nest. See http://mywiki.wooledge.org/BashFAQ/082
no need to test the special variable $?, you can use boolean logic like I do in my snippet

edited Mar 18, 2013 at 19:43

Ansgar Wiechers

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answered Mar 18, 2013 at 19:21

Gilles Quénot

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1 Comment

Logan Over a year ago

Unfortunately, it also leaves the same extra lines.

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