Question 209616 in CentOS Question posted in
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Centos – My while IFS=, command isn't opening a while loop

I’m trying to use the while read command to create a comma separated table of names, routers, and IP addresses. It should then SSH through that series of routers with the router1 value, input a command, and extract the IP addresses it should return, then write them to a file. It is my understanding that I can do this with read.


  grep -v '^#' /opt/pp1/projectprefixed/peeringinfo > /opt/pp1/projectprefixed/$DATE/peeringinfo.conf

while IFS=, read NREN router1 peering
do

  if [ ! -f /opt/pp1/projectprefixed/$DATE/recFromNRENList/$router1 ] 
    then
    ssh -q -n -o StrictHostKeyChecking=no srv_oc_scripts@$router1 "show route recieve-protocol bgp" > $router1
    grep -o [[:digit:]]{3}[.]?[[:digit:]]{3}[.]?[[:digit:]]{3}[.]?[[:digit:]]{3} > $router1
  fi

done < $router1

The table is a text like that looks like this:

NAME1,mx1.ROUTER1,192.168.1.1
NAME2,mx1.ROUTER2,192.168.65.7

However, it returns an "ambiguous redirect" error.

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2

Answers


  1. 0

    Redirection is set up before any command execution is done.
    This implies that the input redirect send to the while-loop is never updated and will always read the initial value of "router1" as input.

    In a simplified form of code, here we create two files, read foo in the while-loop and attempt to change the input file of the while-loop mids run.

    #!/usr/bin/env bash
echo $'barnbaz' > foo
echo $'qux' > bar
f=foo;i=0
while read -r f; do echo $f; f=bar; done < "$f"
grep . *

    This does not work because the while loop’s input is assigned to the file-pointer connected to foo and you cannot change that.

    Where does the error come from? Most likely related to Getting an "ambiguous redirect" error

    Most likely, you forgot to assign router1 before the while-loop or the variable router1, which is local to the while-loop, is empty. This is in agreement with the errors mentioned in the linked question.

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  2. 0

    There are several major logic errors

    1. ssh will consume stdin. Read from a different file descriptor 
      while IFS= read -r NREN router1 peering <&3; do
  ...
done 3< 4router1
    2. router1 appears to be initialized in the read command, but is used as an input file to the loop beforehand, and as the ssh remote host, and as a file name you test for existence, and as the output file for the loop commands. I can’t tell how this file is supposed to exist, and what contents it’s supposed to have
    3. grep will also consume stdin: You probably forgot to specify what input you want for grep

    I want to ssh into a router, run the specified command and pull only the matching pattern and write it to a file. It’s meant to be an IP address

    As a wile stab in the dark, perhaps you want

    ip_regex='([0-9]{1,3}.){3}[0-9]{1,3}'
output_dir="/opt/pp1/projectprefixed/$DATE/recFromNRENList"
router1=???

ip_addr=$(
    ssh -q -n -o StrictHostKeyChecking=no 
        "srv_oc_scripts@$router1" 
        "show route recieve-protocol bgp" 
    | grep -o "$ip_regex"
)
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