1. Overview

In programming, there are different styles of variable naming, such as snake case, Pascal case, and others. Sometimes we may want to convert between them. For this purpose, we can use automated tools such as shell scripts.

In this tutorial, we’ll learn how to convert the snake case naming style to Pascal case in the shell.

2. Snake Case and Pascal Case

Snake case is a naming convention where words are linked via underscore symbols. Each word consists of lowercase letters. For example, the variable this_is_the_string uses the snake case style.

On the other hand, Pascal case is a convention whereby words are linked together without separators, and each word starts with a capital letter. An example of Pascal case is ThisIsTheString.

Now, let’s look at how we can convert from snake case to Pascal case in Linux.

3. Use sed With Regex

We can use the sed command with regular expressions (shortened as regex) to convert from snake case to Pascal case:

$ echo "this_is_the_string" | sed -r 's/(^|_)(.)/\U\2/g'
ThisIsTheString

We can see that the initial snake case string this_is_the_string has been converted to the Pascal case string ThisIsTheString.

Let’s take a closer look at the shell command we’re using:

Now, let’s analyze the regex pattern:

  • (^|_) is the first regex group that matches either the start of the string or an underscore
  • ([0-9a-z]) is the second regex group meaning a single number or lowercase character
  • s/ and /\U\2 means to substitute the above with the uppercase variant of the second regex group
  • g applies the regex globally in the string

Notably, the \U pattern in regex is a GNU extension to POSIX, so it may not be available in non-GNU shells.

Overall, the command above converts the snake case string to the Pascal case string and prints its output to the shell.

4. Use Perl

Perl is a popular alternative to sed when working with regular expressions. The following command converts to Pascal case:

$ echo "this_is_the_string" | perl -pe 's/(?:^|_)./uc($&)/ge;s/_//g'
ThisIsTheString

Let’s look at its regex pattern:

  • (?:^|_). matches any character either at the start of the string or after an underscore
  • uc($&) replaces the whole match with its uppercase version
  • /ge replaces all occurrences in the line and interprets the replacement part as code
  • s/_//g removes any underscores

Overall, the output of this command is similar to what we achieved in the previous example.

5. Use Pure Shell Command

In case we don’t want to utilize any other tools, we can achieve the same goal by using a Bash shell one-liner:

$ uscore="this_is_the_string"; arr=(${uscore//_/ }); printf %s ${arr[@]^}
ThisIsTheString

So, let’s take a closer look at the command:

  • uscore is a variable that stores the initial snake case string
  • ${uscore//_/ } replaces all underscores with spaces and stores the result string in the arr variable
  • ${arr[@]^} converts the first letter of each element to upper case
  • printf %s prints all elements one after another

As a result, we can see that the snake case string is converted to Pascal case correctly.

6. Conclusion

In this article, we learned how to convert the snake case to the Pascal case in the shell.

Firstly, we looked at the sed command with regular expressions. Secondly, we utilized Perl as an alternative to sed. Finally, we looked at pure shell commands that can achieve the same goal.

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