When working with tar archives, you might encounter this puzzling behavior:

# Fails with "Cannot open: No such file or directory"
tar -xvfz archive.tar.gz

# Works perfectly
tar xvfz archive.tar.gz

The GNU tar command actually has two distinct parsing modes:

# Traditional UNIX style (with hyphen)
tar -x -v -f archive.tar -z

# Old-style option clustering (without hyphen)
tar xvzf archive.tar

The critical detail lies in how tar interprets clustered options:

• With hyphen: Each character after - is treated as a separate option
• Without hyphen: The entire cluster is processed as a single option string

This explains why -xvfz fails - it's equivalent to:

tar -x -v -f z archive.tar.gz

For reliable operation across systems, these formats are recommended:

# Explicit style (most compatible)
tar -x -v -z -f archive.tar.gz

# Modern clustered style
tar xvzf archive.tar.gz

# Alternative long options
tar --extract --verbose --gzip --file=archive.tar.gz

This dual parsing mode exists for historical compatibility reasons:

• Early UNIX tar implementations didn't require hyphens
• GNU tar maintains backward compatibility with ancient scripts
• The behavior is documented in man tar under "Old Option Style"

The famous XKCD comic highlights this exact behavior:

# What the comic shows (works)
tar xvzf archive.tar.gz

# What many would expect to work (fails)
tar -xvzf archive.tar.gz

The comic's humor stems from this very inconsistency that baffles many programmers.

When writing scripts that use tar, consider:

#!/bin/bash
# Explicit option style recommended for scripts
tar -x -v -z -f "$1" || {
    echo "Extraction failed" >&2
    exit 1
}

If you've ever encountered this behavior, you're not alone. The GNU tar command exhibits different parsing behavior depending on whether you use the traditional Unix hyphen prefix (-) or omit it entirely. Let's examine what's happening under the hood.

# This fails with "Cannot open: No such file or directory"
tar -xvfz archive.tar.gz

# This works perfectly
tar xvfz archive.tar.gz

The original Unix tar command (dating back to 1979) didn't require hyphens for short options. This legacy behavior persists in GNU tar for backward compatibility. Modern GNU tools typically enforce hyphen usage, but tar maintains special handling.

When you use hyphens, GNU tar follows stricter POSIX guidelines for option parsing. Without hyphens, it uses a more lenient traditional mode:

# POSIX-style (hyphenated) parsing order:
1. -x (extract)
2. -v (verbose)
3. -f (expects filename next)
4. z is interpreted as the filename (error)

# Traditional mode parsing:
1. x (extract)
2. v (verbose)
3. fz (combined as -f -z)
4. Filename is properly recognized

To avoid confusion and ensure consistent behavior across systems:

# Recommended canonical form (works everywhere)
tar -xzvf archive.tar.gz

# Alternative unambiguous forms
tar --extract --gzip --verbose --file=archive.tar.gz
tar -x -z -v -f archive.tar.gz

The famous XKCD comic (#1168) shows tar xvfz because it leverages this legacy parsing behavior. While it appears to violate the "f must be last" rule, the traditional parsing mode treats the options differently.

Looking at GNU tar's source code (version 1.34), this behavior stems from the parse_opt() function in src/tar.c. The parser branches based on whether the first argument begins with a hyphen.

Be aware that BSD tar (used on macOS) and GNU tar (Linux) may handle these edge cases slightly differently. For maximum portability:

# Use separate options for BSD compatibility
tar -x -z -v -f archive.tar.gz

Understanding these nuances helps prevent frustrating debugging sessions and explains why certain "incorrect" commands happen to work.