Need Of Passing Filenames As Arguments In A Shell Script In Ubuntu 20.04
Now, you might be thinking that why do we even need to pass file names as arguments to the shell scripts in the first place. Well, you can have multiple different requirements for which you need to do so. However, the most common use case of doing this is using the “passed” file for reading data from it or writing data to it. For example, you want to create a shell script that calculates the sum of two numbers and stores this sum in a new file. You can actually pass the name of this file to be created as an argument to your shell script while executing this script.
In the same manner, you might want to calculate the total scores of a player in three different football matches. Assume that all of these scores are stored in a text file. Therefore, if you will write a shell script to calculate the total score, then you will first need the data from that text file that you will use to calculate the total. In that case, you will need to read that file first. So, you can easily pass the name of the file to be read as an argument to your shell script while executing it from the terminal.
Methods Of Passing Filenames As Arguments In A Shell Script In Ubuntu 20.04
If you want to pass a file name as an argument to a shell script in Ubuntu 20.04, then depending on your exact need, you can pick any of the following three methods:
Method 1: Passing A Single Filename As Argument
For explaining this method, we have created the shell script shown in the image below:
In this script, we have written the “echo” command for printing a message after the Shebang. Following this command is another “echo” command that is there to print the value of the special variable or the positional parameter “$1”. It means that whichever value will be passed to this shell script from the terminal will be stored in this positional parameter, and as a result of using the “echo” command, this value can also be printed on the terminal.
For executing this shell script in Ubuntu 20.04, we will execute the following command in the terminal:
In this command, Filename.sh represents the name of that shell script that we want to execute whereas Hour.sh is the name of the file that we wanted to pass on to this shell script. You can replace these file names according to the names of your own shell script files.
When you will run the above-mentioned command, the specified shell script will be executed, which in turn will display the name of the shell script file in the output. This will be passed as an argument to this shell script, as shown in the image below:
Method 2: Passing Multiple Filenames As Arguments
This method is basically an extension of our first method. It means that in this method, we will try to pass multiple file names as arguments to a shell script by using the very same technique. For that, the shell script that we have used is shown in the following image:
In this shell script, we simply wanted to print the values of three different positional parameters, i.e., $1, $2, and $3 on the terminal. It means that whichever arguments will be passed on to this shell script from the terminal will be stored in these three positional parameters and as a result of using the “echo” command, these values will also be printed on the Ubuntu 20.04 terminal. Moreover, you can use these positional parameters up to $9 if you wish to pass more than three arguments to your shell script file in Ubuntu 20.04.
Now, to execute this shell script, we will run the command shown below in the terminal:
Here, Filename.sh represents the name of the shell script that we wish to execute; whereas Hour.sh, eof.sh, and EOF.sh refer to the names of the files that we wanted to pass on to this shell script as arguments. You can replace these file names according to the names of your own shell script files.
As soon as this script will be executed with the above-mentioned command, it will display the names of all the arguments passed on to our shell script, i.e., the names of the three files that we have passed on to our shell script, as shown in the following image:
Method 3: Passing The Current Filename As Argument
Instead of passing different file names to a shell script in Ubuntu 20.04, you might just want to use the name of your current file. This file name is already passed as an argument when you execute your shell script and is also stored in a special variable or a dedicated positional parameter, i.e., $0. It means that you do not need to especially pass this filename as an argument, rather, you only need to access it by referencing the $0 parameter of your shell script. For doing so, you can take a look at the shell script shown in the image below:
In this shell script, we have simply used an “echo” command to print a message on the terminal followed by another “echo” command that will print the value of the $0 special variable on the terminal, i.e., the name of your current file.
To execute this shell script, you will have to run the following command in your Ubuntu 20.04 terminal:
Here, Filename.sh corresponds to the name of our current shell script that we want to be executed.
Now, since the name of this file was stored in the $0 special variable, therefore, as a result of executing this shell script, the name of this file will be printed on the terminal, as shown in the image below:
By using these methods, you can conveniently pass file names as arguments to your shell scripts in Ubuntu 20.04. You can use the shell positional parameters ranging from $0 to $9 for achieving this objective. The goal of this tutorial was just to teach you the different methods of passing the file names as arguments to the shell scripts in Ubuntu 20.04. However, you can increase the complexity of the shell scripts shared in this tutorial by using the “passed” file names for serving different purposes.