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Want to terminate command execution when string found in the command output

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Top Forums Shell Programming and Scripting Want to terminate command execution when string found in the command output
# 1  
Old 10-10-2012
Want to terminate command execution when string found in the command output
Hi Experts,

I am very much new to linux scripting, I am currently working on reducing my manual work and hence writing a script to automate few task.

I am running below command to snmpwalk the router..

Code:
snmpwalk -v 3  -u WANDL_SU -a MD5 -A vfipmpls -x DES -X VfIpMpLs -l authPriv 182.19.96.13 |grep ae0.784

get below output..

Code:
Did not find 'MplsVpnName' in module MPLS-VPN-MIB (/usr/local/share/snmp/mibs/mib-jnx-ldp.txt)
IF-MIB::ifDescr.2500 = STRING: ae0.784
Timeout: No Response from 182.19.96.13

this command finds the string and show it in output..but when I run below command..

Code:
snmpwalk -v 3  -u WANDL_SU -a MD5 -A vfipmpls -x DES -X VfIpMpLs -l authPriv 182.19.96.13 |grep ae0.784 |awk '{print $2}'

get below output..

Code:
Did not find 'MplsVpnName' in module MPLS-VPN-MIB (/usr/local/share/snmp/mibs/mib-jnx-ldp.txt)
Timeout: No Response from 182.19.96.13
=

command is verymuch fine..but i am not getting why it shows timeout when i try to print 2 column...

also one more requirement is program should terminate once match is found and also print given column in some output file..

looking for help from the experts...

thanks in advance!!!

Regards,
Hanuamnt
Last edited by Scrutinizer; 10-10-2012 at 07:47 AM.. Reason: code tags
# 2  
Old 10-10-2012
Code:
Did not find 'MplsVpnName' in module MPLS-VPN-MIB (/usr/local/share/snmp/mibs/mib-jnx-ldp.txt)
IF-MIB::ifDescr.2500 = STRING: ae0.784
Timeout: No Response from 182.19.96.13

Not all those lines which you get in the output are seen by the grep command. The 1st and 3rd lines have been written by your command snmpwalk to standard error (by default the terminal). The 2nd line has been filtered by the grep command.

Is this what you need?
Code:
snmpwalk -v 3  -u WANDL_SU -a MD5 -A vfipmpls -x DES -X VfIpMpLs -l authPriv 182.19.96.13 2>/dev/null|awk '/ae0\.784/{print $NF}'

# 3  
Old 10-10-2012
If you want a command to terminate after some output has been detected ...

If the command will continue to generate output after the match is found, and if the wait time (could be a fraction of a second, could be weeks) until the command next attempts to write data to a pipe is acceptable, then a simple filter (awk, sed, etc...), which exits immediately after finding the match, could be sufficient. When the command next attempts to write to the pipe, since the filter that was on the other end is now gone, it will be sent a SIGPIPE (default response to this signal is program termination).

If the command to be killed does not write to the pipe regularly, then you need to send it a signal yourself when the match is detected. For this, you need to know the PID of that command.

Regards,
Alister
# 4  
Old 10-10-2012
thanks all for the reply..
Hi team,

thanks elixir_sinari

the below command given by elixir works for me but in my output I want
some other column to be displayed(it is displaying the same output as i m searching for) and also it should write it to some other file, for e.g. output will be like..
IF-MIB::ifDescr.2500 = STRING: ae0.784

then I want highlighted part to be displayed in output..


snmpwalk -v 3 -u WANDL_SU -a MD5 -A vfipmpls -x DES -X VfIpMpLs -l authPriv 1.1.1.1 2>/dev/null|awk '/ae0\.784/{print $NF}'

Kindly help on this.

thanks..
# 5  
Old 10-10-2012
Not every awk out there allows for this, but you can try to set the awk field separator to "[: ]" and then print $3.
Last edited by RudiC; 10-11-2012 at 04:57 AM.. Reason: typo
# 6  
Old 10-14-2012
Hi RudiC,

thanks for the reply...could you please write same command and put awk whereever require..I am not getting where to use awk as suggested by you...

thanks in advance!!!

Regards,
Hanumant
# 7  
Old 10-14-2012
As elixir_sinari and alister pointed out, there are some improvements possible to your command line to get where you want.
  1. Two of the three lines you show in post #1 are error msgs output to stderr. No piped filter will see those unless you redirect stderr.
  2. The grep cmd is pointless. awk can do this.
  3. If you want do stop after the first matched output, you could close the pipe.
Given your post #1 sample, my comments to elixir_sinari's suggestion combined with alister's might do the job:
Code:
snmpwalk -v 3  -u WANDL_SU -a MD5 -A vfipmpls -x DES -X VfIpMpLs -l authPriv 182.19.96.13 2>/dev/null|awk -F"[: ]" '/ae0\.784/{print $3; exit}' > outputfile

It will suppress error msgs, print the ifDescr.2500 to the outputfile as desired, and then exit and close the pipe, (hopefully) causing the snmpwalk cmd to terminate. Pls check out and come back with results.
Last edited by RudiC; 10-14-2012 at 02:35 PM..
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