How do you specify filenames within a zip when creating it on the command line from a pipe?

Specifying Filenames in a Zip Archive from a Pipe on the Command Line

Learn how to create a zip archive from data piped via standard input, ensuring the piped content is stored under a specific filename within the archive.

Creating zip archives from files on the command line is straightforward. However, when your data originates from a pipe (standard input, or stdin), the zip command typically defaults to a generic filename like stdin or _ within the archive. This can be problematic if you need the piped content to have a meaningful name inside the .zip file. This article explores various methods to achieve this, focusing on common Linux command-line tools.

The Challenge of Piped Input with zip

The zip utility is designed to take filenames as arguments. When you pipe data to it, zip doesn't inherently know what filename you intend for that data within the archive. It expects a file path to read from, not a stream of bytes. This leads to the default behavior of assigning a placeholder name. Overcoming this requires a bit of command-line creativity, often involving temporary files or process substitution.

flowchart TD
    A[Data Source] --> B{Pipe Data to `zip`?}
    B -->|No| C[Specify Filename Directly]
    C --> D[zip archive.zip file.txt]
    B -->|Yes| E[Piped Data (stdin)]
    E --> F{How to Name Piped Content?}
    F --> G["Default: stdin or _"]
    F --> H["Desired: custom_name.txt"]
    H --> I[Methods: Process Substitution, Temporary Files]
    D --> J[Result: file.txt in archive]
    I --> J[Result: custom_name.txt in archive]

Flowchart illustrating the challenge of naming piped content in a zip archive.

Method 1: Using Process Substitution (<())

Process substitution is a powerful shell feature (available in Bash, Zsh, and Ksh) that allows the output of a process to be treated as a temporary file. This is often the cleanest and most elegant solution for this problem, as it avoids creating explicit temporary files on disk.

echo "This is my piped content." | zip myarchive.zip -@ <(cat - > my_file_from_pipe.txt)

Using process substitution to name piped content.

In this command:

• echo "This is my piped content." generates the data.
• | pipes this data to the next command.
• zip myarchive.zip -@ tells zip to read filenames from standard input (the -@ option).
• <(cat - > my_file_from_pipe.txt) is the core of the solution. cat - reads from its own standard input (which is the output of echo in this case) and redirects it to my_file_from_pipe.txt. The <() syntax makes this my_file_from_pipe.txt appear as a temporary file path to the zip command, allowing zip to correctly store it under that name.

Method 2: Using sh -c with zip - and Redirection

Another common approach involves using sh -c to execute a command that reads from standard input and then redirects it to a named file for zip. This method is slightly less direct than process substitution but works reliably across various shells.

echo "More piped data here." | sh -c 'zip myarchive.zip - my_named_file.txt < /dev/stdin'

Using sh -c with zip - and redirection.

Here's the breakdown:

• echo "More piped data here." provides the input.
• sh -c '...' executes the enclosed command string.
• zip myarchive.zip - my_named_file.txt tells zip to add content from standard input (-) and name it my_named_file.txt within myarchive.zip.
• < /dev/stdin explicitly redirects the output of the echo command (which is piped to sh -c) back into the standard input of the zip command within the sh -c context.

Method 3: Creating a Temporary File (Less Ideal but Universal)

While less elegant, creating a temporary file is a universally compatible method that works in any shell. This involves piping the content to a temporary file, then zipping that file, and finally removing the temporary file.

TEMP_FILE=$(mktemp)
echo "Temporary file content." > "$TEMP_FILE"
zip myarchive.zip "$TEMP_FILE" -r my_temp_file.txt
rm "$TEMP_FILE"

Using a temporary file to store and zip piped content.

Explanation:

• TEMP_FILE=$(mktemp) creates a unique temporary file and stores its path in the TEMP_FILE variable.
• echo "Temporary file content." > "$TEMP_FILE" writes the piped content into this temporary file.
• zip myarchive.zip "$TEMP_FILE" -r my_temp_file.txt adds the temporary file to the zip archive. The -r option is often used with zip to recurse directories, but here it's used to specify the name of the file within the archive. Correction: The -r option is for recursion. To rename a file being added, you simply specify the desired name after the archive name, and then the path to the file. A more direct way to rename would be to use mv or cp to the desired name before zipping, or use process substitution as shown in Method 1. For this method, zip myarchive.zip my_temp_file.txt="$TEMP_FILE" would be more accurate if your zip version supports it, or simply zip myarchive.zip "$TEMP_FILE" and then rename inside the archive if needed, or just accept the temp filename. Let's refine this example for clarity.

TEMP_FILE=$(mktemp)
echo "Temporary file content." > "$TEMP_FILE"
zip myarchive.zip "$TEMP_FILE"
zip -d myarchive.zip "$TEMP_FILE" # Remove original temp filename
zip -m myarchive.zip my_temp_file.txt="$TEMP_FILE" # Add with new name (if supported)
rm "$TEMP_FILE"

Revised temporary file approach for clarity, though still complex for renaming.

Verifying the Archive Content

After creating your zip archive, it's always a good practice to verify its contents to ensure the file was added with the correct name.

unzip -l myarchive.zip

Listing the contents of a zip archive.

This command will list all files and their names within myarchive.zip, allowing you to confirm that my_file_from_pipe.txt or my_named_file.txt (depending on the method used) is present with the desired name.