Using last command. An IP address is a codename assigned to a computer on a network. At last we send the e-mail template we just created with: sendmail -vt < ~/mail.txt. -eq 0 ] then /root/scripts/test1.sh exit 0 fi done It works as a postal address, ensuring that network traffic is sent to the correct computer. 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.. bash if -f #!/bin/bash . It will check after if the command succeeds. 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. Example – Strings Equal Scenario 3.) It is useful to verify A record and provides warning if ‘A’ record is not same on all master / slave nameservers. This shell script uses host DNS lookup utility to check A record for given domain / host against all nameservers. ping works with both IPv4 and IPv6. Something like that: while true; do ping -c1 google.com if [ $? 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. if [ -f / home / tutorialkart / sample.txt ]; then echo "sample.txt - File exists." And here goes the e-mail body, test test test.. 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. 2. By passing the parameters '-c 30' to ping, it will try 30 ping and stop. 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. if statement when used with option f , returns true if the length of the string is zero. Is it possible possible to ping an 192.168.1.254:80 or 192.168.1.254:23 ports? One can test that a bash variable starts with a string or character in bash efficiently using any one of the following methods. That's it - you can now test sendmail from command line and even send full e-mails including headers from Linux/UNIX shell. I think it is best to do a loop that contains one ping and check if this ping succeed. Below is an example of how the simple sendmail test could look like on a live system: I wanted to see if a specific port of a desktop computer or server is open from a Linux or Unix command line shell. How do I ping a specific port? Names of users and tty's can be given, in which case last will show only those entries matching the arguments. In this tutorial you will learn how to find your IP address using a Linux operating system. $ cat /etc/hostname daygeek-Y700 Method-4: Check the HostName using uname Command in Linux. bash if -f : Check if file exists and is a regular file. 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. Hello, I am trying to develop a script to check for valid hostnames. You can have as many commands here as you like. @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. Check the current hostname using /etc/hostname file. 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