@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. It is useful to verify A record and provides warning if ‘A’ record is not same on all master / slave nameservers. Following example proves the same. By passing the parameters '-c 30' to ping, it will try 30 ping and stop. ping works with both IPv4 and IPv6. 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. Bash Strings Equal – In this tutorial, we shall learn how to check if two strings are equal in bash scripting.. Bash Strings Equal. -eq 0 ] then /root/scripts/test1.sh exit 0 fi done You can have as many commands here as you like. Names of users and tty's can be given, in which case last will show only those entries matching the arguments. Below is an example of how the simple sendmail test could look like on a live system: In this tutorial you will learn how to find your IP address using a Linux operating system. How do I ping a specific port? An IP address is a codename assigned to a computer on a network. 2. Using last command. One can test that a bash variable starts with a string or character in bash efficiently using any one of the following methods. 3.) 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. It will check after if the command succeeds. bash if -f : Check if file exists and is a regular file. I think it is best to do a loop that contains one ping and check if this ping succeed. 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.. It works as a postal address, ensuring that network traffic is sent to the correct computer. That's it - you can now test sendmail from command line and even send full e-mails including headers from Linux/UNIX shell. 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. I wanted to see if a specific port of a desktop computer or server is open from a Linux or Unix command line shell. For example, "en.wikipedia.org" is a hostname. Check the current hostname using /etc/hostname file. Something like that: while true; do ping -c1 google.com if [ $? 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. if [ -f / home / tutorialkart / sample.txt ]; then echo "sample.txt - File exists." 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. Example – Strings Equal Scenario Is it possible possible to ping an 192.168.1.254:80 or 192.168.1.254:23 ports? bash if -f #!/bin/bash . And here goes the e-mail body, test test test.. 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. 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