Redirect shell command output

Nitin Namdev — Tue, 16 May 2023 09:11:36 +0000

Shell scripts provide a very powerful feature: the ability to redirect the output from commands and scripts and send it to files, devices, or even as input to other commands or scripts.

Types of output
Commands and scripts in a shell can generate two basic types of outputs:

STDOUT: The normal output from a command/script (file descriptor 1)
STDERR: The error output from a command/script (file descriptor 2) By default, STDOUT and STDERR are sent to your terminal's screen.

Redirect STDOUT

For the following examples, I will use this simple set of files:

$ls -la file*
-rw-r--r--. 1 admin2 admin2  7 Mar 27 15:34 file1.txt
-rw-r--r--. 1 admin2 admin2 10 Mar 27 15:34 file2.txt
-rw-r--r--. 1 admin2 admin2 13 Mar 27 15:34 file3.txt

I'm running a simple ls commands to illustrate STDOUT vs. STDERR, but the same principle applies to most of the commands you execute from a shell.

I can redirect the standard output to a file using ls file* > my_stdout.txt:

$ls file* > my_stdout.txt

$ cat my_stdout.txt 
file1.txt
file2.txt
file3.txt

Next, I run a similar command, but with a 1 before >. Redirecting using the > signal is the same as using 1> to do so: I'm telling the shell to redirect the STDOUT to that file. If I omit the file descriptor, STDOUT is used by default. I can prove this by running the sdiff command to show the output of both commands side by side:

$ls file* 1> my_other_stdout.txt

$sdiff my_stdout.txt my_other_stdout.txt
file1.txt                        file1.txt
file2.txt                        file2.txt
file3.txt                        file3.txt

Send STDOUT and STDERR to the same file

Another common situation is to send both STDOUT and STDERR to the same file:

$ls file* non-existing-file* > my_consolidated_output.txt 2>&1

$ cat my_consolidated_output.txt 
ls: cannot access 'non-existing-file*': No such file or directory
file1.txt
file2.txt
file3.txt

In this example, all output (normal and error) is sent to the same file.

The 2>&1 construction means "send the STDERR to the same place you are sending the STDOUT."

Ansible Sandbox for Developing Custom Module

Nitin Namdev — Mon, 15 May 2023 17:47:34 +0000

Hello all,

Today ansible is the most popular tool in the automation part, so for creating playbook, roles and modules you need to do too much manual work, for getting rid from this I have created a script that will create a ansible role structure with tasks, handlers, deafults, template and library

And also I created a hello custom module that is called in the task so you can work without any manual work, you can directly run the command and you will have ready to go ansible environment.

Simply run the following command —

cd /opt/
wget -O - https://raw.githubusercontent.com/vortexdude/src/main/script.sh | bash -s newrole

After running the above command in your linux you need the package of ansible and wget and git.

to run the ansible playbook —

ansible-playbook ansible/main.yml

also it will create the inventory file where you can define you all of the servers the path of the inventory will be inventory/all.

hello.py is your custom module and the file wll be in the following location

vi ansible/roles/newrole/library/hello.py

DEV Community: Nitin Namdev

Redirect shell command output

Redirect STDOUT

Send STDOUT and STDERR to the same file

Ansible Sandbox for Developing Custom Module