How do you handle different line endings and character encodings in cross-platform shell scripts?

1 Line endings

Line endings are the characters that mark the end of a line in a text file. The most common ones are LF (line feed, \n), CR (carriage return, \r), and CRLF (CR followed by LF, \r\n). Different platforms use different line endings by default: Linux and Mac use LF, Windows uses CRLF, and some older systems use CR. If you write a shell script with the wrong line endings, it may not run properly or cause unexpected results. For example, if you write a script with CRLF on Windows and try to run it on Linux, you may get an error like "bad interpreter: No such file or directory" because the shell interprets the CR as part of the script name. To avoid this, you can use a text editor or a tool like dos2unix or unix2dos to convert the line endings to the appropriate format for the target platform. Alternatively, you can use a shebang line (#!) at the beginning of your script to specify the interpreter and the -r option to ignore the CR characters.

2 Character encodings

Character encodings are the systems that map text characters to binary codes. The most common ones are ASCII, UTF-8, and UTF-16. ASCII is the oldest and simplest encoding, but it only supports 128 characters, mostly English letters and symbols. UTF-8 is the most widely used encoding today, and it can represent over a million characters from different languages and scripts. UTF-16 is another encoding that can support many characters, but it uses two bytes per character instead of one or more as in UTF-8. If you write a shell script with a different encoding than the one expected by the platform or the terminal, you may see garbled or missing characters, or get errors like "invalid multibyte character". To avoid this, you can use a text editor or a tool like iconv or recode to convert the character encoding to the appropriate one for the target platform. Alternatively, you can use a BOM (byte order mark) at the beginning of your script to indicate the encoding and the -N option to enable multibyte support.

3 Quoting and escaping

Quoting and escaping are the techniques that allow you to use special characters in shell scripts without causing syntax errors or unwanted expansions. Special characters are the ones that have a specific meaning or function in the shell, such as spaces, quotes, asterisks, dollar signs, backslashes, and so on. Quoting is the process of enclosing a string of characters in single or double quotes to prevent the shell from interpreting them as special characters. Escaping is the process of prefixing a special character with a backslash to cancel its special meaning. However, quoting and escaping can be tricky when you write cross-platform shell scripts, because different platforms may have different rules and conventions for them. For example, Windows uses backslashes as path separators, while Linux and Mac use slashes. If you write a script with backslashes on Windows and try to run it on Linux or Mac, you may get errors like "command not found" or "no such file or directory" because the shell interprets the backslashes as escape characters. To avoid this, you can use forward slashes as path separators in your scripts, as they are compatible with all platforms. Alternatively, you can use double quotes and double backslashes to preserve the backslashes as literals.

4 Testing and debugging

Testing and debugging are the processes of verifying and rectifying errors and bugs in your shell scripts. When you create cross-platform shell scripts, testing and debugging can be more arduous and time-consuming, as you must test your scripts on different platforms and environments, and tackle various line endings, character encodings, quoting, and escaping issues. To make testing and debugging simpler and faster, you can use tools such as ShellCheck, a static analysis tool that detects syntax errors, style issues, and potential bugs. Additionally, Bash -x enables debug mode and prints each command with its arguments before executing it; Bash -n checks for syntax errors without running the script; Bash -v prints each line of your script as it is read; echo prints a message or a variable value to the standard output or a file; printf prints a formatted message or a variable value to the standard output or a file; read reads a line of input from the standard input or a file and assigns it to a variable; cat prints the contents of a file or concatenates multiple files; od prints the byte values of a file or input in different formats such as hexadecimal or octal; file determines the file type and encoding of a file or input. By utilizing these tools and techniques, you can test and debug cross-platform shell scripts more effectively and efficiently.

5 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?