How to tell if a string is not defined in a bash shell script

#!/bin/bash

if [ -z $1 ]; then
        echo 'Enter something please.';
        exit 1;
fi;

How to set a BASH variable equal to the output from a command?

In addition to the backticks, you can use $(), which I find easier to read, and allows for nesting.

OUTPUT=$(ls -1)
echo $OUTPUT

 

 

You can use eval to execute a string:

eval $illcommando

bash split string into array

IFS=', ' read -a array <<< "$string" /* array is the variable name */

To access an individual element:

echo "${array[0]}"

To iterate over the elements:

for element in "${array[@]}"
do
    echo "$element"
done

To get both the index and the value:

for index in "${!array[@]}"
do
    echo "$index ${array[index]}"
done

The last example is useful because Bash arrays are sparse. In other words, you can delete an element or add an element and then the indices are not contiguous.

unset "array[1]"
array[42]=Earth

The Bash script does not delete all entries from a csv file

I am trying to patch a bunch of CENT OS machines with the latest fix pack. I have the below bash script that takes csv file as a input which has the ip address and password for those machines.

The code works fine however, it would only work for the first row it does not seem to be working for the rest of the list as my output.txt only has the entry only for the first row host .

patch.sh

INPUT=hosts_test.cvs
OLDIFS=$IFS
IFS=,
[ ! -f $INPUT ] && { echo "$INPUT file not found"; exit 99; }
while read privateip password
do

sshpass -p$password ssh -t -o "StrictHostKeyChecking no" user123@$privateip "

hostname
hostname -I --all-ip-addresses
sudo yum -y update bash
env x='() { :;}; echo vulnerable' bash -c \"echo If you see the word vulnerable above, then you are vulnerable to shellshock\"
echo ""
exit

" >> output.txt

done < $INPUT
IFS=$OLDIFS

hosts_test.cvs

10.xxx.xx.219,abcd~qY1
10.xxx.xx.226,l4~abcdefg
10.xxx.xx.221,l4@abcdefgh

Terminal Output

Pseudo-terminal will not be allocated because stdin is not a terminal.

---

Add at the end of your sshpass command </dev/null.