Unix & Linux Stack Exchange is a question and answer site for users of Linux, FreeBSD and other Un*x-like operating systems. Output of the above program. In this example, the variable count specifies a condition that is used as part of the if statement.Before the if statement is executed, the variable count is assigned the value 5.The if statement then checks whether the value of count is 5.If that is the case, the statement between the keywords then and fi are executed.Otherwise, any statements following the if statement are executed. Greetings. To know more about lsblk, head to its man page. Conclusion # Checking if a string contains a substring is one of the most basic and frequently used operations in Bash scripting. Use /dev/null to send any unwanted output from program/command and syntax is: command >/dev/null This syntax redirects the command standard output messages to /dev/null where it is ignored by the shell. The -q option tells grep to be quiet, to omit the output. Here, in this tutorial, we have discussed several command line option this tool offers. But if you want to test whether a command succeeded or not, use the command itself directly with if, as shown above. After reading this tutorial, you should have a good understanding of how to test … test.sh #!/usr/bin/env bash if [ $# -ge 3 ] then echo script has at least 3 arguments fi produces the following output Write a Bash script so that it receives arguments that are specified when the script is called from the command line. About Himanshu Arora It's probably the most common command to use in an if, which can lead to the assumption that it's part of the shell's syntax. For example, I used the nm command with the 'apl' binary file: nm apl. The following screenshot shows the kind of output the above command produced: Bash check if process is running or not. The branching of the test command is significant. to negate the test as well, to prevent us having to use else as well: # Best if ! The following script demonstrates how this works. grep -q regex options; then printf '%s\n' 'myscript: Pattern not found!' >&2 exit 1 fi It only takes a minute to sign up. [is itself a command, very nearly equivalent to test. Enter a number: 45 Number is odd. Explanation of the above code-We have asked a user to enter a number and stored the user response in a number variable. The basic usage of this command is very straight forward - all you have to do is to run the 'nm' command and pass the name of the object file as input to it. If your Linux work involves accessing information related to block devices, then lsblk is a must know command for you. 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. You can have as many commands here as you like. Enter a number: 88 Number is even. The aforementioned command produced the following output: Conclusion. 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