How to Replace file Extension in Bash using `basename`

The aim of this page📝 is to explain extension replacement in shell scripting based on the particular example of replacing a file extension with .sh.

• To replace an extension in a file, you can use parameter expansion in shell scripting.
• The correct syntax to replace an extension is ${markdown_file//.md/.sh}, where .md is replaced with .sh.
• Another approach is to use the basename command to extract the file without the path and extension.
• You can concatenate the new extension to the extracted file to replace the extension.
• The basename command is used to strip the directory and suffixes from files.
• To remove a specific extension using basename, you need to specify the extension value you want to remove. basename "${markdown_file}" .md removes the .md extension from the variable which can be a full absolute path to the file.

function msh {
    local markdown_file="$1"
    if [[ "${markdown_file: -2}" != "md" ]]; then
        echo "~~> ${markdown_file} is not a markdown file"
        return 1
    fi
    shell_file="$(basename "$markdown_file" .md).sh"
    touch "$shell_file"
    echo "~~> ${shell_file} created"
}

• As for the tests, the correct way to extract the last 2 characters of a string is ${markdown_file: -2} using negative indices in parameter expansion.
• Note the danger of using ${markdown_file:-2} . There, a hyphen - is for parameter expansion with a default value, not for extracting the last characters.

LINKS

https://www.gnu.org/software/coreutils/manual/html_node/basename-invocation.html#basename-invocation