Category: Linux Notes

There are instances where you want to quickly locate and move specific file types from point A to Point B.

Example:

Move all PHP files from /home/$user/php-files/ to /home/$user/php-mv-files

Easiest way to do this is to use the Find command in terminal.

$ find ./ -name "*.php"

./php-files/file3.php
./php-files/file2.php
./php-files/file1.php

This lists all the PHP files in the /php-files directory.

To move the files, you run the following command:

$ find ./php-files/ -name "*.php" -exec mv {} ./php-mv-files/ \;

This will move all files from ./php-files to ./php-vmv-files. Running the original Find command will get you the following:

$ find ./ -name "*.php"
./php-mv-files/file3.php
./php-mv-files/file2.php
./php-mv-files/file1.php

In this instance, -exec mv {} says, run the MV command on the files selected from the original find, that’s what the {} implies. You then escape, and close the command using \;. This final piece is critical to stopping the command.

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Path environmental variables are variables that function like a shortcut for your system. They allow you to define directories where executables are located.

Assume you installed this application picc-9.82.9453-linux.run. Without setting the path you’d have to run this every time in your terminal:

# /usr/hitech/picc/9.82/bin/picc

Instead of:

# picc

Running picc without having to define the path every time is so much easier, and faster. To achieve this experience you have to add the application executable to the Path environmental variable.

The first option is edit your user profile:

$ vim ~/.bash_profile

It will look something like this:

# .bash_profile

# Get the aliases and functions
if [ -f ~/.bashrc ]; then
. ~/.bashrc
fi

# User specific environment and startup programs

PATH=$PATH:$HOME/bin

export PATH

You are looking to edit this section:

PATH=$PATH:$HOME/bin

Update the path with new application location (e.g., /usr/hitech/picc/9.82/bin) using the colon (:) as the separator.

PATH="$HOME/bin:$PATH:/usr/hitech/picc/9.82/bin"

Save the file, and try running the command in your terminal.

# picc

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Whenever you’re working with linux you’ll find yourself in need of running tasks repeatedly. The easiest way to do this is to set up a recurring job using Cron.

A crontab file contains instructions for the cron(8) daemon in the following simplified manner: “run this command at this time on this
date”. – Cron Man Page

You can edit your cron jobs using crontab, specifically:

# crontab -e

If you have any other cron jobs you’ll see other entries. If not, you’ll be able to create your own entries using your favorite editor (e.g., VIM, Nano, VI, etc…).

The format for a cron entry is as follows:

minute hour day-of-month month day-of-week command

There is a great tutorial available here: https://crontab.guru/every-1-hour

If I want to run a job every hour, this is the entry I’d add to Cron:

0 * * * * cd /root/scripts && ./checkrunningprocess.sh

If you ever want to see what jobs you have running you can run:

crontab -l

and you’d see something like this:

# crontab -l
0 * * * * cd /root/scripts && ./checkrunningprocess.sh

Happy automating!

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When you’re working with linux you might have to add a user to different group.

Let’s say that you want to create user John, and you want John to have root abilities. To do this you’re going to want to add the user, John, to the sudoers group.

The sudoers group controls who has Sudo privileges on a machine. Sudo is a command that allows a user to run commands based on another users privileges, in most instances it is configured to run as root. Fun fact, SUDO was established from “superuser do.”

To add user John to the sudoers group you would do something like this:

# usermod -aG sudoers John

The two options used include:

• a – Add the user to the supplementary group(s). Use only with the -G option.
• G – A list of supplementary groups which the user is also a member of. Each group is separated from the next by a comma, with no intervening whitespace.

You have to use both options in conjunction with each other. You can find a more detailed list of options here: https://linux.die.net/man/8/usermod

This same model applies to any group and can be used for any user. A great example is Apache on a web server. 🙂

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If you are looking for specific content but can’t remember where it’s located on the server, this post is for you. It will show you how to find specific text anywhere in a folder, or server.

We are going to use the GREP command when doing searches in linux.

grep searches input files for lines containing a match to a given pattern list. When it finds a match in a line, it copies the line to standard output (by default), or produces whatever other sort of output you have requested with options.

Do you ever find yourself wanting to do advanced searches in Linux? In the last article we shared how to use grep to find specific text. In this article we’ll introduce AWK.

The awk command is a powerful method for processing or analyzing text files—in particular, data files that are organized by lines (rows) and columns. Simple awk commands can be run from the command line. More complex tasks should be written as awk programs (so-called awk scripts) to a file.

If you have ever tried to run the current directory (CD) command inside your shell script you’ll notice it doesn’t work.

Example

#!/bin/bash
cd /home/$user/Documents/test-directory

This is because shell scripts run inside a subshell, and each subshell has its own concept of what the “current directory” is. In fact, it’s not that the cd doesn’t execute, it actually does but the minute it exits the subshell you’re back in the original shell and nothing changed.