In this tutorial you will learn how to find your IP address using a Linux operating system. To check if two strings are equal in bash scripting, use bash if statement and double equal to == operator.. To check if two strings are not equal in bash scripting, use bash if statement and not equal to!= operator.. 2. Is it possible possible to ping an 192.168.1.254:80 or 192.168.1.254:23 ports? How do I ping a specific port? One can test that a bash variable starts with a string or character in bash efficiently using any one of the following methods. last searches back through the file /var/log/wtmp (or the file designated by the -f flag) and displays a list of all users logged in (and out) since that file was created. ping works with both IPv4 and IPv6. Below is an example of how the simple sendmail test could look like on a live system: It is useful to verify A record and provides warning if ‘A’ record is not same on all master / slave nameservers. It works as a postal address, ensuring that network traffic is sent to the correct computer. I wanted to see if a specific port of a desktop computer or server is open from a Linux or Unix command line shell. Following example proves the same. Below are the prerequisites for a valid hostname which I got from wiki : Hostnames are composed of series of labels concatenated with dots, as are all domain names. Line 6 - The backslash ( \ ) in front of the single quote ( ' ) is needed as the single quote has a special meaning for bash and we don't want that special meaning. if [ -f / home / tutorialkart / sample.txt ]; then echo "sample.txt - File exists." bash if -f : Check if file exists and is a regular file. @0xC0000022L: Nobody "keeps me" from doing that, but the answer specifically suggests hosts, and so far 4 people have upvoted vinc17's comment expressing the pain caused by "suddenly IPv6".Being prepared for IPv6 is not always the issue: many programs need a way to determine whether two names/addresses refer to the same host. if statement when used with option f , returns true if the length of the string is zero. This shell script uses host DNS lookup utility to check A record for given domain / host against all nameservers. Hello, I am trying to develop a script to check for valid hostnames. Using last command. You can have as many commands here as you like. Something like that: while true; do ping -c1 google.com if [ $? Check the current hostname using /etc/hostname file. And here goes the e-mail body, test test test.. An IP address is a codename assigned to a computer on a network. You use the ping command to send ICMP ECHO_REQUEST packets to network computers, routers, switches and more. For example, "en.wikipedia.org" is a hostname. Introduction – In bash, we can check if a string begins with some value using regex comparison operator =~. I think it is best to do a loop that contains one ping and check if this ping succeed. Let's break it down: Line 4 - Let's see if the first command line argument is greater than 100; Line 6 and 7 - Will only get run if the test on line 4 returns true. -eq 0 ] then /root/scripts/test1.sh exit 0 fi done Names of users and tty's can be given, in which case last will show only those entries matching the arguments. That's it - you can now test sendmail from command line and even send full e-mails including headers from Linux/UNIX shell. Example – Strings Equal Scenario 3.) At last we send the e-mail template we just created with: sendmail -vt < ~/mail.txt. uname (stands for unix name) is an utility that prints the system information like name, version and other details about the system and the operating system running on it. bash if -f #!/bin/bash . Bash Strings Equal – In this tutorial, we shall learn how to check if two strings are equal in bash scripting.. Bash Strings Equal. $ cat /etc/hostname daygeek-Y700 Method-4: Check the HostName using uname Command in Linux. By passing the parameters '-c 30' to ping, it will try 30 ping and stop. Given, in which case last will show only those entries matching the arguments – in bash, we check...: check if this ping succeed including headers from Linux/UNIX shell, routers, switches and more a string with. 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