Tag: linux

Staging the changes in git

git status

git add -A stages all changes

git add . stages new files and modifications, without deletions

git add -u stages modifications and deletions, without new files

git add -A is equivalent to git add .; git add -u

git add -A is equivalent to git add --all

git add -u is equivalent to git add --update

References
https://stackoverflow.com/questions/572549/difference-between-git-add-a-and-git-add
https://git-scm.com/docs/git-stage
https://git-scm.com/docs/git-add

Signing Commits in Git using GPG Key

gpg --list-secret-keys --keyid-format LONG

From the list of GPG keys, copy the GPG key ID you’d like to use. In this example, the GPG key ID is 3AA5C34371567BD2

$ gpg --list-secret-keys --keyid-format LONG
/Users/hubot/.gnupg/secring.gpg
------------------------------------
sec   4096R/3AA5C34371567BD2 2016-03-10 [expires: 2017-03-10]
uid                          Hubot 
ssb   4096R/42B317FD4BA89E7A 2016-03-10
git config --global user.signingkey 3AA5C34371567BD2

or

git commit -S -m your commit message

References
https://help.github.com/en/articles/telling-git-about-your-signing-key
https://git-scm.com/book/en/v2/Git-Tools-Signing-Your-Work
https://help.github.com/en/articles/signing-commits

Save terminal output to a file

          || visible in terminal ||   visible in file   || existing
  Syntax  ||  StdOut  |  StdErr  ||  StdOut  |  StdErr  ||   file   
==========++==========+==========++==========+==========++===========
    >     ||    no    |   yes    ||   yes    |    no    || overwrite
    >>    ||    no    |   yes    ||   yes    |    no    ||  append
          ||          |          ||          |          ||
   2>     ||   yes    |    no    ||    no    |   yes    || overwrite
   2>>    ||   yes    |    no    ||    no    |   yes    ||  append
          ||          |          ||          |          ||
   &>     ||    no    |    no    ||   yes    |   yes    || overwrite
   &>>    ||    no    |    no    ||   yes    |   yes    ||  append
          ||          |          ||          |          ||
 | tee    ||   yes    |   yes    ||   yes    |    no    || overwrite
 | tee -a ||   yes    |   yes    ||   yes    |    no    ||  append
          ||          |          ||          |          ||
 n.e. (*) ||   yes    |   yes    ||    no    |   yes    || overwrite
 n.e. (*) ||   yes    |   yes    ||    no    |   yes    ||  append
          ||          |          ||          |          ||
|& tee    ||   yes    |   yes    ||   yes    |   yes    || overwrite
|& tee -a ||   yes    |   yes    ||   yes    |   yes    ||  append
  • command > output.txt

    The standard output stream will be redirected to the file only, it will not be visible in the terminal. If the file already exists, it gets overwritten.

  • command >> output.txt

    The standard output stream will be redirected to the file only, it will not be visible in the terminal. If the file already exists, the new data will get appended to the end of the file.

  • command 2> output.txt

    The standard error stream will be redirected to the file only, it will not be visible in the terminal. If the file already exists, it gets overwritten.

  • command 2>> output.txt

    The standard error stream will be redirected to the file only, it will not be visible in the terminal. If the file already exists, the new data will get appended to the end of the file.

  • command &> output.txt

    Both the standard output and standard error stream will be redirected to the file only, nothing will be visible in the terminal. If the file already exists, it gets overwritten.

  • command &>> output.txt

    Both the standard output and standard error stream will be redirected to the file only, nothing will be visible in the terminal. If the file already exists, the new data will get appended to the end of the file..

  • command | tee output.txt

    The standard output stream will be copied to the file, it will still be visible in the terminal. If the file already exists, it gets overwritten.

  • command | tee -a output.txt

    The standard output stream will be copied to the file, it will still be visible in the terminal. If the file already exists, the new data will get appended to the end of the file.

  • command |& tee output.txt

    Both the standard output and standard error streams will be copied to the file while still being visible in the terminal. If the file already exists, it gets overwritten.

  • command |& tee -a output.txt

    Both the standard output and standard error streams will be copied to the file while still being visible in the terminal. If the file already exists, the new data will get appended to the end of the file.

References
https://askubuntu.com/questions/420981/how-do-i-save-terminal-output-to-a-file

Keep Alive SSH Sessions

To keep an SSH connection alive, you can modify your SSH configuration to send periodic keepalive messages. Here are a few methods to achieve this:

Method 1: Modify the SSH Client Configuration

  1. Edit the SSH client configuration file (/etc/ssh/ssh_config or ~/.ssh/config): 
    nano ~/.ssh/config
  2. Add the following lines to send keepalive messages every 60 seconds: 
    Host *
    ServerAliveInterval 60
    ServerAliveCountMax 3
    • ServerAliveInterval specifies the interval in seconds between keepalive messages.
    • ServerAliveCountMax specifies the number of keepalive messages that can be sent without receiving a response from the server before the connection is terminated.

Method 2: Modify the SSH Server Configuration

  1. Edit the SSH server configuration file (/etc/ssh/sshd_config): 
    sudo nano /etc/ssh/sshd_config
  2. Add or modify the following lines to keep the server alive: 
    ClientAliveInterval 60
ClientAliveCountMax 3
    • ClientAliveInterval specifies the interval in seconds that the server will wait before sending a null packet to the client to keep the connection alive.
    • ClientAliveCountMax specifies the number of client alive messages which may be sent without receiving any messages back from the client.
  3. Restart the SSH service to apply the changes: 
    sudo systemctl restart sshd

     

Taking Command Line Arguments in Bash

Pass arguments through to another program

#!/bin/bash
# print_args.sh
echo "You provided the arguments:" "$@"

# You could pass all arguments to another program like this
# myProgram "$@"

Get the number of arguments passed

#!/bin/bash
echo "You provided $# arguments"

Accessing a specific argument by index

#!/bin/bash
echo "Arg 0: $0"
echo "Arg 1: $1"
echo "Arg 2: $2"

Argument 0 is the name of the script being invoked itself.

Iterating through each argument

#!/bin/bash
for arg in "$@"
do
    echo "$arg"
done

Check arguments for specific value

#!/bin/bash
for arg in "$@"
do
    if [ "$arg" == "--help" ] || [ "$arg" == "-h" ]
    then
        echo "Help argument detected."
    fi
done

References
https://www.devdungeon.com/content/taking-command-line-arguments-bash