How to know if the script command has been successfully executed?

Question

I need the script to identify whether the tar.gz file was successfully generated in an if. Here’s a non-functional example:

VAR=tar -zcf teste.tar.gz teste/testeDir
if [VAR]
then
echo "Sucesso"
else
echo "Erro"
fi

Very simple I think but could not do! I await answers...

Answer 1

Use the variable $? it returns "0" if the last command was successfully executed, and returns "1" if there was an error in this command.

Below is a table with these special variables that are available in the shell:

Variable Description

• $0 Parameter number 0 (command or function name)
• $1 Parameter number 1 (from command line or function)
• ... Parameter number N of the command line or function)
• $9 Parameter number 9 (from command line or function)
• ${10} Parameter number 10 (from the command line or function)
• $# Total number of command line or function parameters
• $* All parameters, as a single string
• $@ All parameters such as multiple strings protected
• $$ PID of the current process (from the script itself)
• $! PID of the last process in the background
• $_ Last argument of last executed command
• $? Return value of last executed command

see this example of the cat command on my terminal:

felix@asgard:[~]: cat escrever.py 
arq = open('arquivo.txt','w')
arq.write("Pyhton é legal")
arq.close()
felix@asgard:[~]: echo $?
0
felix@asgard:[~]: cat escreve.py 
cat: escreve.py: No such file or directory
felix@asgard:[~]: echo $?
1

In the example below I only put the result of "success" because in my tests, when I tried to compress a non-existent file or even putting wrong arguments to compress, simply the command was not executed, 'breaking' thus the script:

#!/bin/bash

tar -zcf escrever.tar.gz escrever.py

if [ $? -eq 0 ]
then
    echo "sucesso"
fi