从可变输出获取特定行

Question

I need to get a line from a commands output that is assigned to a bash variable.

#Gets the netstat values for the UPD packages
UDP_RAW_VALUE=`netstat -su`

##TRYING THIS BUT TOTALLY FAILED.
echo "$UDP_RAW_VALUE" | sed -n "$2"p 

I just need to get a specific value from one of the command executions, which is

UDP_RAW_VALUE=`netstat -su`

The output of this specific command is like this:

-bash-4.2$ bash MyBashScript
IcmpMsg:
    InType0: 14464
    InType3: 12682
    InType8: 101
    InType11: 24
    OutType0: 101
    OutType3: 34385
    OutType8: 15840
Udp:
    931752 packets received
    889 packets to unknown port received.
    0 packet receive errors
    1007042 packets sent
    0 receive buffer errors
    0 send buffer errors
    IgnoredMulti: 647095
UdpLite:
IpExt:
    InMcastPkts: 1028470
    InBcastPkts: 552859
    InOctets: 233485843587
    OutOctets: 75548840236
    InMcastOctets: 44792084
    InBcastOctets: 167490770
    InNoECTPkts: 317265390
    InECT0Pkts: 25289
    InCEPkts: 686361

Simply, I need to read the numeric value of the 931752 packets received result, excluding the "packets received" part. I have tried doing some regular expression. Then found this sed which looks promising but I have no idea how to use it, in terms of regular expression. I am pretty sure I need to complete this with regex.

I need the numerical value because I will compare a previous and current value and check if the difference is between the threshold. If not, send the mail.

Answer 1

Just add this:

 PACKETS_RECEIVED=$(echo "${UDP_RAW_VALUE}" | sed -n 's/^ *\([0-9][0-9]*\) packets received$/\1/p')

It will print the content that you saved from the RAW output of the command. the "" are important or it will print all the output in one line which is not what you want.

The sed command -n says do not print the lines by default. the s///p command tells is to substitute the pattern between the first two / / with the \\1 , which is the group in the pattern that is between \\( and \\) ; in our case that would be the number you want.

The PACKET_RECEIVED=$() part tells bash to run what is between the $() and assign the output to the variable.

Answer 2

perhaps another sed solution if you dont mind?

UDP_RAW_VALUE=`netstat -su|sed -n '/Udp/{n;s/[^0-9\n]//g;p}'`

/Udp:/ #find all lines that have Udp

n # get the next line delete all all characters leaving you number

p #print

or awk

   UDP_RAW_VALUE=`netstat -su|awk '$0~/Udp:/{getline;print $1}'`