如何在bash中拒绝空数组索引

Question

I wrote the bash like so:

#!/bin/bash
GAP=1
Out=$1
ResultFile=$2

len=`wc -l $Out | awk '{print $1}'`
eval "(COMMAND) &"
pid=$!

i=0
while kill -0 $pid; do
    if [ -N $Out ]; then
        newlen=`wc -l $Out | awk '{print $1}'`
        newlines=`expr $newlen - $len`
        tail -$newlines $Out > temp
        IP=( $(sed -n '<SomeThing>' temp) )
        host=${IP[$i]}
            echo "exit" | nc $host 23
            if [ "$?" -eq "0" ]; then
                    (
                           <DoingSomeThing>

            ) | nc $host 23 1>>$ResultFile 2>&1
            fi
    len=$newlen
    let i++
    fi
sleep $GAP
done

When the command IP=( $(sed -n '<SomeThing>' temp) ) is running in my bash maybe the result of sed command is nothing and maybe the output is ip . I want only when output of sed command get ip write it into array and when the output of sed is empty does not write it to array.

Thank you

Answer 1

You're not doing your script right in many ways but about your question, the quick way is to store the output first on a variable:

SED_OUT=$(sed -n '<SomeThing>' temp)
[[ -n $SED_OUT ]] && IP=($SED_OUT) ## Would only alter IP if $SED_OUT has a value.