Bash how many parameters

Leo Commands can be builtin, and can be not. In bash, [ is a builtin, while [[ is a keyword. In some older shells, [ is not even builtin. Commands like [ naturally co-exist as an external command in most systems, but internal commands are prioritized by the shell unless you bypass with command or exec.

Check the shell's documentation on how they evaluate. Take note of their difference, and how they may behave differently in every shell. Dave I agree but the subshell is unnecessary.

If it doesn't have to undergo word splitting and filename expansion then it should be quoted regardless if its expanded value is expected to be unaffected by such processes or not.

Show 2 more comments. Aleks-Daniel Jakimenko-A. Why might that be a good idea, in the present case? Considering efficiency, portability and other issues, isn't it best to use the simplest and most universally understood syntax, i. If you're for some reason limited, then surely you can use [ ] instead, but keep in mind that then you shouldn't use [[ ]] also.

I hope you understand the pitfalls of [ ] and reasons why these features exist. Dave Yeah. I was young and dumb : Edited. Add a comment. It also happens to work with FreeBSD test , but may not work on foo test. If the shell option nocasematch is enabled, the match is performed without regard to the case of alphabetic characters. Any part of the pattern may be quoted to force it to be matched as a string. If you're only interested in bailing if a particular argument is missing, Parameter Substitution is great:!

Pat Pat DwightSpencer Would it matter? Temak I can if you have specific questions, but the linked-to article explains it better than I can.

Dwight Spencer Dwight Spencer 1, 15 15 silver badges 22 22 bronze badges. If you have another set of lines after that line, that would be wrong since exit 1 would only apply to the context of the subshell making it just synonymous to usage; false.

Don't get me wrong if one way works fine for you then use it but remember not everyone uses the same implementation of bash that you do and we should code to posix standards not bashisms.

I'm not sure what you're saying. You are a life saver. My scenario was that I made functions in my script and the script takes an argument, which is the used in the last function called in the script. Thanks again. Add to this case statement to delineate the end of each option. Testing is now a little more complex. You need to test your program with several different options—and no options—to see how it responds.

First, check to ensure that with no options that it prints "Hello world! That works as expected, so now try some testing to see what happens when you enter some unexpected options. The program just ignores the options for which you haven't created specific responses without generating any errors.

Although in the last entry with the -lkjsahdf options, because there is an "h" in the list, the program did recognize it and print the help text.

Testing has shown that one thing that is missing is the ability to handle incorrect input and terminate the program if any is detected. You can add another case stanza to the case statement that will match any option for which there is no explicit match. This general case will match anything you haven't provided a specific match for. The case statement now looks like this. This bit of code deserves an explanation about how it works. It seems complex but is fairly easy to understand.

The while — done structure defines a loop that executes once for each option in the getopts — option structure. The ":h" string —which requires the quotes—lists the possible input options that will be evaluated by the case — esac structure. Each option listed must have a corresponding stanza in the case statement. In this case, there are two. One is the h stanza which calls the Help procedure. After the Help procedure completes, execution returns to the next program statement, exit;; which exits from the program without executing any more code even if some exists.

The option processing loop is also terminated, so no additional options would be checked. If any options are entered that are not recognized, this stanza prints a short error message and exits from the program. Any additional specific cases must precede the final catch-all.

I like to place the case stanzas in alphabetical order, but there will be circumstances where you want to ensure that a particular case is processed before certain other ones.

The case statement is sequence sensitive, so be aware of that when you construct yours. The last statement of each stanza in the case construct must end with the double semicolon ;; , which is used to mark the end of each stanza explicitly.

This allows those programmers who like to use explicit semicolons for the end of each statement instead of implicit ones to continue to do so for each statement within each case stanza. Be sure to test this version of your program very thoroughly. Use random input and see what happens. You should also try testing valid and invalid options without using the dash - in front. First, add a variable and initialize it.

Add the two lines shown in bold in the segment of the program shown below. Add the logic to input a name in a moment but first test the program again. The result should be exactly the same as before. This new stanza does not have an exit statement. This changes the program flow so that after processing all valid options in the case statement, execution moves on to the next statement after the case construct.

Be sure to test the help facility and how the program reacts to invalid input to verify that its ability to process those has not been compromised. If that all works as it should, then you have successfully learned how to use options and option arguments.

In this article, you've used positional parameters to enter data into the Bash program during invocation from the command line and used options to direct the flow of the program as well as to enter data into the program.

You added a help function and the ability to process command line options to display the help selectively. And you added an optional argument that allows entering a name on the command line. This little test program is designed to be simple, so you can easily experiment with it yourself to test this input method on your own. As an exercise, revise the program to take a first name and last name. Try entering the options for first and last names in reverse order to see what happens.

He is a strong proponent of and evangelist for the "Linux Philosophy. Relive our April event with demos, keynotes, and technical sessions from experts, all available on demand. Enable Sysadmin. Adding arguments and options to your Bash scripts. Exploring methods for getting data into scripts and controlling the script's execution path for better automation and script management.

Image by Gerd Altmann from Pixabay. Basically, the [email protected] special variable can hold all the arguments that are passed to a Bash script. To understand this, you can take a look at the following Bash script that we have designed for you:.

In this Bash script, we have simply printed the value of the [email protected] special variable, i. To see how this modified Bash script works, we have again executed it with the same parameters as we did in the two examples above. When this script was executed, the output turned out to be exactly the same as we had in our second example. The modified Bash script is shown in the image below:. To test this Bash script and visualize its output, we executed it with the same parameters as we did in our first three examples.

This time also when our Bash script was executed, its output was the same as that of our second and third examples, as you can see from the following image:. To understand this phenomenon, you will have to go through the Bash script shown in the image below:. We wanted to test all three conditions of this Bash script. For that, we have first executed this script with three parameters, and the corresponding output is shown in the following image:. After that, we executed this Bash script with four arguments, because of which an error message was printed on the terminal as shown in the image below:.