[wplug] BASH question

[Henry Umansky]

The backslash at the end of a line indicates that the line continues to the 
next line.  Only in string sequences does the backslash mean an escape 
character.  In order to check the return status of a command, type "echo 
$?".  For example:

$ date
Thu Jul 10 09:02:51 EDT 2003
$ echo $?
0
$ false
$ echo $?
1
$echo $?
0

Notice the two echo commands in a row, but the second one returns a zero 
(success), that is because the $? variable gets updated after every 
command, so it shows that the previous echo command was successful.

-Henry

--On Thursday, July 10, 2003 8:55 AM -0400 "Wise, Jeremey" <WISEJ at PIOS.com> 
wrote:r

> Thanks. This is what I needed. Just a few questions.
>
> 1) The line "...-f1 > \ /root/ipaddy.tmp". I believe the "\" is an escape
> to ensure that the  "/root/.." will be treated as a path. Is that correct.
> 2) How did you know that "/usr/sbin/adsl-status" would return zero if link
> up? Is this normal or is their a way to check this return code for any
> application run?
>
> Thanks,
>
> Jeremey Wise (440)-519-6006
> (CNE,MCSE,CSE)
> Pioneer-Standard Electronics, Inc
> wisej at pios.com
>
> IBM ED PACK -Part # SB033 $4,500 ... SP Discount 11%
> IBM ED CARD - Part # SB218 $8,995 ... SP Discount 8.5%
>
> -----Original Message-----
> From: Mike Griffin [mailto:mike at dmrnetworks.com]
> Sent: Wednesday, July 09, 2003 6:47 PM
> To: wplug at wplug.org
> Subject: RE: [wplug] BASH question
>
> Here's a script that I made yesterday and does basically the same thing.
> I have this script running every hour, and on boot. You'll want to
> create the files ipaddy and ipaddy.tmp with the current IP before
> running this script.
>
># !/bin/bash
>
> /sbin/adsl-status 	# If our link is down, the return error will
> 				# NOT be zero
>
> if [ $? -ne 0 ]
> then
>   /usr/sbin/adsl-start	# Bring up our link
>   /usr/sbin/ifconfig eth0 | grep inet | cut -d\: -f2 | cut -d' ' -f1 > \
>   /root/ipaddy.tmp
> fi
>
># Let's compare IP adress of our ipaddy and ipaddy.tmp files
> old="`cat /root/ipaddy`"
> new="`cat /root/ipaddy.tmp`"
>
> if [ "$old" != "$new" ]
> then
>    # This line is in addition to my script. Will mail whoever the new IP
>   /usr/bin/mail -s "IP has changed" someonehere at somewhere.com < \
>   /root/ipaddy.tmp
>   cp -f /root/ipaddy.tmp /root/ipaddy
>   # We'll want to rerun our firewall rules for the new IP.
>   /etc/iptables
> fi
>
> exit 0
>
>
> -----Original Message-----
> From: wplug-admin at wplug.org [mailto:wplug-admin at wplug.org] On Behalf Of
> Wise, Jeremey
> Sent: Wednesday, July 09, 2003 4:56 PM
> Cc: 'WPLUG'
> Subject: RE: [wplug] BASH question
>
> Ok so let me see if I understand.
>
> ************
># Script to bring up Landmark's Internet
># 07-09-2003
># v0.1
> Internetstatus=($(adsl-status |grep up|cut -f 4 -d ' '))
> InternetIP=($(ifconfig ppp0 |grep inet |cut -f 2 -d : |cut -f 1 -d ' '))
> curDate=`date +"%y-%m-%d"`
> curTime=`date +"%H%M"`
>
> if $Internetstatus= up ;then
>    printf The Internet link is up!
>       if [ ! $InternetIP = ($(cat /root/CurrentIP.txt)) ;then
>        echo $InternetIP >/root/CurrentIP.txt
>        echo $InternetIP |mail -s "New IP Address" wisej at pios.com
>       fi
>    ;else
>    echo The Internet link is down:$curDate$-$curTime >>/var/log/messages
> fi
> ***********
> 1) You were saying that to make a variable equal to a string (such as an
> IP
> address) I need to run the whole command in backets ie. Subshell
> ex:(ifconfig ppp0 |grep inet |cut -f 2 -d : |cut -f 1 -d ' ') This does
> work
> now... thx.
> 2) My syntax errors; lack of space, lack of closing bracket did not seem
> to
> fix the next step where I attempt a comparison of $InternetIP to ($(cat
> /root/CurrentIP.txt)) and it fails. Is my logic right but syntax wrong?
>
> Thanks,
>
> Jeremey Wise (440)-519-6006
> (CNE,MCSE,CSE)
> Pioneer-Standard Electronics, Inc
> wisej at pios.com
>
> IBM ED PACK -Part # SB033 $4,500 ... SP Discount 11%
> IBM ED CARD - Part # SB218 $8,995 ... SP Discount 8.5%
>
> -----Original Message-----
> From: Bob Schmertz [mailto:rschmertz at speakeasy.net]
> Sent: Wednesday, July 09, 2003 4:19 PM
> To: Wise, Jeremey
> Cc: WPLUG
> Subject: Re: [wplug] BASH question
>
> Wise, Jeremey incurred the wrath of Bob on Jul 9, by saying
>
>> Another stupid question. I am trying to write a script that detects if
> a
> DSL
>> line is down if it is start it. If the IP rotates email it to me so I
> can
>> know how to get to it if I need to.
>>
>> ***************
>># !/bin/bash
>># Script to bring up Landmark's Internet
>># 07-09-2003
>># v0.1
>> Internetstatus="adsl-status |grep up|cut -f 4 -d ' '"
>> InternetIP="ifconfig ppp0 |grep inet |cut -f 2 -d : |cut -f 1 -d ' '"
>
> You probably want to put this whole thing in back quotes (or $(this)
> notation), rather than double quotes.  On the other hand, if you don't
> want this to be evaluated yet, why don't you just put this line later in
>
> the script?
>
>> curDate=`date +"%y-%m-%d"`
>> curTime=`date +"%H%M"`
>>
>> if $Internetstatus=up ;then
>>   printf The Internet link is up!
>>      if [! $InternetIP=(cat /root/CurrentIP.txt)] ;then
>
> Spaces.  There must be a space after the [.  Apparently there musst also
>
> be spaces on either side of the = comparison operator (while there
> should be no spaces in assignment).  And, looks like you left out a $
> sign in front of your open parenthesis ( "$(cat /root/CurrentIP.txt)" )
>
>>       echo $InternetIP >/root/CurrentIP.txt
>>       echo $InternetIP |mail -s "New IP Address" wisej at pios.com
>>      fi
>>   ;else
>>   echo The Internet link is down:$curDate-$curTime >>/var/log/messages
>> fi
>> ****************
>>
>> My issues are
>> 1) I can run the command "ifconfig ppp0 |grep inet |cut -f 2 -d : |cut
> -f 1
>> -d ' '" at a shell prompt and get an ok response but it does not run. I
>> tried to put it in brackets (subshell) but that does not work either
>> 2) Logic does not hold; " if [! $InternetIP=(cat /root/CurrentIP.txt)]
>> ;then". How does one do this? How can I check a string output against
> an
>> existing variable string or integer?
>
> --
> Cheers,
> Bob Schmertz
>
>
> _______________________________________________
> wplug mailing list
> wplug at wplug.org
> http://www.wplug.org/mailman/listinfo/wplug
>
> _______________________________________________
> wplug mailing list
> wplug at wplug.org
> http://www.wplug.org/mailman/listinfo/wplug
> _______________________________________________
> wplug mailing list
> wplug at wplug.org
> http://www.wplug.org/mailman/listinfo/wplug



Henry Umansky
University of Pittsburgh
Computing Services and Systems Development
hmust2 [at] pitt [dot] edu
(412) 624 -4357