Connexion
Sed is an acronym for "stream editor." A stream refers to a source or destination for bytes. In other words, sed can read its input from standard input (stdin), apply the specified edits to the stream, and automatically output the results to standard output (stdout). Sed syntax allows an input file to be specified on the command line. However, the syntax does not directly support output file specification; this can be achieved through output redirection or editing files in place while making a backup of the original copy optionally. Sed is one of the most powerful tools on Linux and Unix-like systems. Learning it is worthwhile, so in this tutorial, we will start with the sed command syntax and examples.
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The post Linux Sed Tutorial: Learn Text Editing with Syntax & Examples appeared first on nixCraft.
How do I change MySQL root password under Linux, FreeBSD, OpenBSD and UNIX-like like operating system over the ssh session?
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Most Linux and UNIX-like system configuration files are documented using comments, but sometimes I just need to see a line of configuration text in a config file. How can I view just the uncommented configuration file directives from squid.conf or httpd.conf file? How can I strip out comments and blank lines on a Linux or Unix-like system?
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The post Linux / UNIX View Only Configuration File Directives ( Uncommented Lines of a Config File ) appeared first on nixCraft.
How can I copy one hard disk to another using the dd, ddrescue, or dcfldd commands?
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The post Linux Copy One Hard Disk to Another Using dd Command appeared first on nixCraft.
LXD or Incus is a Linux operating system-level container system. You can build over 25+ Linux distros for testing, fun, and profit. You can even run GUI apps inside those containers and get output displayed back to your X display easily. For example, you can run Firefox in one Linux container for banking needs with custom add-ons, including specific firewall rules just for allowing outgoing banking and nothing else. You can have another container to run Chromium/Edge/FF for social media. Of course, it is not a replacement for something like Qubes OS, but you can do many things in an isolated environment. You can try a new Linux distro without the VM's overheads and test new features offered by that distro. All Linux containers will share the same Linux kernel and hardware devices as your GPU. Here is a quick shell script to build a quick lab to test various Linux distros.
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The post Shell script to set up an LXD / Incus (Linux Containers) lab for testing purpose appeared first on nixCraft.
Here is a quick and dirty shell script I put to check LXD or Incus container size and how much space they are taking on the BTRFS subvolume. Naturally, you must run the script as a root user, and LXD or Icnus must be configured with BTRFS storage backend on Linux operating systems. See how to set up and install LXD on Ubuntu 20.04 LTS or installing Incus on Debian 12/11 using the apt command.
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The post How To check LXD/Incus container BTRFS disk usage on Linux appeared first on nixCraft.
Here is a handy and useful Linux and Unix shell script that reduce PDF file size using Ghostscript. No need to upload your PDF file to the shady third-party website. Just do it from the terminal. I tested it with both CentOS and Ubuntu/Debian Linux. It should work with macOS, FreeBSD and other Unix-like systems as long as you have the Ghostscript installed.
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TTL is an acronym for Time-To-Live (TTL) in DNS. It sets the time in seconds that a DNS record is allowed to be cached by DNS resolvers (caching server) before it needs to be fetched again from the authoritative name server. In other words, longer TTL can reduce the load on authoritative DNS servers and improve response times by keeping records in the cache longer. The shorter TTL is useful for frequently changing DNS records, as it ensures that updates are propagated quickly across the Internet. Say you want to see the Time-To-Live (TTL) value for a given DNS record for A, AAAA, and MX. Here is a sample shell script that works on Linux, Unix, and macOS. You must have the bash and dig command installed.
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The post Shell script to see Time-To-Live (TTL) for a DNS record on Linux, Unix, macOS and FreeBSD appeared first on nixCraft.
Here is a simple shell script to notify secondary read-only replica (slave) MariaDB server health status failure via email and push notification. Master-slave data replication allows you to copy databases to multiple MariaDB servers. It is useful for backup, data recovery, load balancing, and much more. See how to configure SSL-protected MariaDB replication between a master and slave server.
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The post Shell script to monitor MariaDB replication and send email alert about server health status appeared first on nixCraft.
How do I capture a specific protocol or port, such as 80 (HTTP) or 443 (HTTPS), using the TCPDump tool under Linux/UNIX? How do I record traffic with TCPDump and find problems later on with my network or server issues? Let's dive into the nitty-gritty of capturing and analyzing your network traffic for trapshooting network and server issues.
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The post TCPDump: Capture and Record Specific Protocols / Port Traffic appeared first on nixCraft.
I am a new macOS Unix user. I am writing a small bash shell script. How do I download file directly from the command-line interface using curl? How can I download file with cURL on a Linux or Unix-like systems?
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I need to copy or clone file ownership and permissions from another file on Linux. Is there a bash command line option to clone the user, group ownership and permissions on a file from another file on Linux operating system?
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The post How to copy permissions from one file to another on Linux appeared first on nixCraft.
I have a valuable tip for you on extracting the filename and extension in Bash when using Linux, macOS, FreeBSD, or Unix-like systems. It's quick and easy to follow.
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The post How to get and extract filename extension in Bash appeared first on nixCraft.
Let us see how to check for ssh connectivity in a shell script running under macOS, FreeBSD, or Linux/Unix desktop using BatchMode=yes and ConnectTimeout=$VALUE options. This simple trick helps write a wrapper script that does other things, such as making a backup or running external command agents such as Salt or Ansible to do other tasks.
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While working on the bash shell script wrapper, I needed to ensure that I only passed an integer in the Bash script under Linux and Unix-like systems. Here is how to check if a number is an integer in Bash Linux or Unix script or at the command-line interface (CLI)
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The post Bash see if an input number is an integer or not appeared first on nixCraft.
Today I will talk about a common problem faced by many Linux or Unix sysadmins and developers. Typically modern apps and security devices heavily depend upon APIs and lists that feed data in JSON format. For example, a list of spamming or VPN CIDRs or a good list of verified bots' IP CIDRs is in JSON format. If they accept JSON format, you can take this list and upload it to your router or WAF. Unfortunately, not all devices accept JSON format. Hence, we can take JSON format and convert it to CSV format per our needs.
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The post How to convert JSON to CSV using Linux / Unix shell appeared first on nixCraft.
So I have this specific use case where I get data in a comma-separated values (CSV) file. I pick up the company name, address, telephone, email, and some other data from that file. Once data is collected, I create a final pdf using a simple script. Unfortunately, data comes with unwanted leading and trailing white spaces in each field. So my final pdf file gets messed up because of those white space. Let us see how to trim leading and trailing white space for a string in Bash running on Linux or Unix machines.
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At a certain point, I needed to change the VLAN IP address such as 172.0.0.2 with 172.0.0.1 for ease of use. As you know, Linux and Unix-like operating system stores all IP addresses and config in plain text files. This page explains my little adventure where I had to find and find and replace ALL IP addresses with a new one on Linux.
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The post How to find and replace ALL IP addresses with a new one appeared first on nixCraft.
Let us say you want to repeat a character such as '-' OR '=' multiple times while writing bash script. Please note that I needed a quick script to work on Linux, macOS, and FreeBSD server to repeat a string/character n times. One simple way to to repeat a string or character n times is simple use the echo command/printf command as follows:
Lateo.net - Flux RSS en pagaille (pour en ajouter : @ moi) echo '------------------------------------'
printf '%s\n' '------------------------------------'
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The post How to repeat a character ‘n’ times in Bash appeared first on nixCraft.
How can I check if a file does not exist in a Bash script?
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I need to set a bash environment variable called PURGEIMAGE and take specific actions in my script. For example, if PURGEIMAGE set, then purge images from CDN else just URL. I am going to call my script as PURGEIMAGE=yes ./purgecache.sh url1 url2. So how do I know if a bash variable set at the CLI and used in my bash script running on Linux or Unix-like systems?
The post How to check if bash variable defined in script appeared first on nixCraft.
I have two columns (fields) in my text file. I am trying to insert '|
FOO This is a description
BAR Another description for bar
TEXT Another description for TEXT
So I ran awk '{ print $1 "|"; $1=""; print}' input > output but print command is adding a new line:
FOO|
This is a description
BAR|
Another description for bar
TEXT|
Another description for TEXT
Is there any way to tell awk not to print a newline and create the file? Here is what I want so that I can create final HTML table based upon '|'
FOO|This is a description
BAR|Another description for bar
TEXT|Another description for TEXT
The post How to force awk not to print a newline appeared first on nixCraft.
ShellCheck is easy to use, free, and open-source static analysis tool that automatically finds bugs in your shell scripts. If you write shell scripts for automation or containers, you need this tool. Let us see how to install and use ShellCheck on the FreeBSD development Unix server.
The post How to install ShellCheck on FreeBSD – A shell script static analysis tool appeared first on nixCraft.
I need to define a bash variable called failed and set the value to False. When my script is called from a cron job, specific tasks might fail, and then I need to flip failed to True. Based upon $failed, I need to send an email alert that my cron job has failed. So how can I declare and use Boolean variables in a shell script running on a Linux server?
The post How to declare Boolean variables in bash and use them in a shell script appeared first on nixCraft.
I have many PDF files, and I need to convert them to a png file format, add a border to those images, and convert back all those images to pdf format. How can I convert pdf to image format on Linux and vice versa using the CLI?
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How do I check the TLS/SSL certificate expiration date from my Linux or Unix shell prompt? How can I find the TLS certificate expiry date from Linux and Unix shell scripts?
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How do I write the output into the file in Linux bash shell? Can you explain I/O redirection for both bash and POSIX shell to write data to the file under Unix or Linux?
The post How to write the output into the file in Linux appeared first on nixCraft.
I brought eggs from the market, and it says best before 20 days from the date of packing. Say my egg box was packed on 29/July/2020. How do I add days to date using Linux CLI? I want to find out date 29/July/2020 + 20days using the CLI, and how do I do it?
The post How to add days to date and get new date on Linux appeared first on nixCraft.
How can I find the correct ulimit values for a user account or process on Linux systems?
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How do I extract tar.xz files in Linux? Can you tell me command to unzip linux-5.6.13.tar.xz file? How can I uncompressing (or decompressing) all files in the current directory?
The post How to extract tar.xz files in Linux and unzip all files appeared first on nixCraft.
My Nginx web server is behind a reverse proxy server. How do I restore the original and real IP address of my client/visitors when behind a reverse proxy server such as AWS Cloudfront, Fastly, Cloudflare CDN/WAF?
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I need to remove the last character from a line and shell variable such as "${_allowed_ips}". For example, each line is as follows in my file:
foo,
bar,
demo,
I need output as follows:
foo
bar
demo.
How can I use sed to delete the last character?
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The post How to save terminal output to a file under Linux/Unix appeared first on nixCraft.
Let us test your basic knowledge of Linux systems, including commands.
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Can you explain DEBIAN_FRONTEND apt or apt-get variable? How and why I need to use this in Docker or shell scripts under a Debian and Ubuntu Linux?
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How do I see how many processes are running in Linux? How can count all running processes in Linux?
The post How do I count how many processes are running in Linux? appeared first on nixCraft.
I set up a new cloud server, but my auto-completion of bash shell commands are not working. How do I enable autocomplete feature in CentOS 8 (CentOS Enterprise Linux 8)? How do I write simple bash completion code in CentOS 8?
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I need to find and return the PID of the last command executed in Linux. How do I return the PID of command in Linux?
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How do I extract filename and extension in the Bash shell script from the given path? How can I get filename from the path under the bash shell?
The post Bash get filename from given path on Linux or Unix appeared first on nixCraft.
How can I find a website's DNS address? How do I check the current DNS servers of a domain or website using a Linux or macOS command line option? How do I find DNS address of a website using bash?
The post How to find a website’s DNS (name server) address appeared first on nixCraft.
I need to get public IPv4 address on current EC2 or Lightsail VM Linux/Unix instance. How do I find Public IP address AWS EC2 or Lightsail VM?
The post How to find Public IP address AWS EC2 or Lightsail VM appeared first on nixCraft.
I noticed that my default shell set to zsh on Macos Catalina. How do I change my default shell to bash on Macos Catalina using the command line or GUI options?
The post Change default shell to bash on Macos Catalina appeared first on nixCraft.
I want to start command called foo, and kill it if still running after given DURATION in seconds. How do I run a command a time Limit on Linux? How do I run a Linux command, and have it timeout (abort) after N seconds?
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I am trying to delete a directory in Linux using the rmdir dir1 command. But, I am getting an error that read as follows:
rmdir: failed to remove `dir1': Directory not empty
How do I force remove and delete a directory in Linux?
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I need to check if a directory exists or not, within a shell script running on Linux or Unix-like system? How do I check if a directory exists in a shell script?
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I am new to Linux programming and bash shell commands. I have a folder structure as dir1, dir2, dir3 and I would like to rename it as dir001, dir002, dir003. How do you rename multiple folders in Linux?
The post How to rename multiple folders in Linux using command line appeared first on nixCraft.
Can you explain bash exit status code? How do I set bash exit status in my Linux shell scripts?
The post Linux bash exit status and how to set exit status in bash appeared first on nixCraft.
I installed Linux on Intel NUC. I need to find Intel NUC BIOS version. How do I find out BIOS version, date, and model name of my Intel NUC using Linux command-line options?
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I am a new Linux user. How do I hide files and directories in Linux operating systems using the command line interface?
The post How to hide files and directories in Linux appeared first on nixCraft.
I am a new to shell scripting. How do I check for NULL value in a Linux or Unix shell scripts?
The post Bash shell find out if a variable has NULL value OR not appeared first on nixCraft.
