— Vs -: The Subtle Syntax Differences In Linux Commands

Deciphering Dashes: – vs —

In Linux command line syntax, the humble dash plays an important role. Both the single dash “-” and double dash “–” are used to specify command options, but they function differently. Understanding when to use each dash type can unlock the full power and flexibility of Linux commands.

This article will examine the distinct purposes of the single and double dash options. We’ll overview the origins of the convention, study option parsing rules, show common use cases, and reveal best practices for crafting reliable, readable commands.

Overview of Dash Types

The single dash “-” preceding a word indicates a short, single-character command option. The double dash “–” denotes a long, multi-character option name. This enables a compact and extended syntax for the same function:

tar -x   # Short option
tar --extract  # Long option equivalent 

Single dashes concatenate multiple short options. Double dashes separate long options and read more like sentences:

gzip -9 -c file   # Multiple short options
gzip --best --stdout file # Long option alternative

This convention originated in Unix and was adopted for the GNU project and Linux. It aims to balance human and computer parsing needs in a command grammar.

Single Dash Options

The defining quality of single-dash options is that they start with a single hyphen, followed by a single alphanumeric character that identifies the option.

Single dashes take the form of:

-X

Where “X” is a single, alphanumeric option code, like:

-a 
-b
-1

Some rules for single-dash options:

• Can directly concatenate without spaces: -abc
• Case sensitive: -a vs -A may differ
• Can represent the negation with capital letter: -r vs -R

The benefits include:

• Concise syntax
• Easy to type and chain
• First option codes standardized across commands

The downsides involve:

• Opaque meaning
• Easy to forget codes
• Ambiguity risks with capital letters

Double Dash Options

In contrast, double dash options have longer, descriptive names that start with two hyphens:

--descriptive-option-name

Rules for double dash options are:

• Must be preceded by whitespace or follow another option
• Made up of alphanumeric words joined by hyphens
• Case sensitive
• Can be abbreviated to a unique prefix

So valid double dash options resemble:

--extract
--simulate
--output-file
--max-depth  

Or abbreviated versions like:

  
--extr
--sim  
--outp-f
--max-d

The advantages of double dash options include:

• Self-documenting
• Easy to discover
• Explicit in meaning

The disadvantages involve:

• More verbose
• Longer to type
• Not standardized across commands

When to Use Each Type

The single and double dash types serve complementary purposes. Single dashes provide an easy access shortcut for common options. Double dashes offer expressive clarity.

It is preferable to use single dashes for:

• Frequently needed arguments
• Targeting an expert user base
• Conserving screen space in dense command lines

It is best to utilize double dashes when:

• Self-documenting complex operations
• Enabling menu-driven discovery
• Scripting for long-term maintenance

Ultimately most Linux commands implement a mix of both dash types to fulfill simplicity and explicitness design goals.

Examples

ls -a vs ls –all

The ls directory listing command displays file and folder names. By default ls hides dotfiles and folders that start with a “.” period character.

The -a option shows these hidden entries. And --all provides the same effect:

$ ls         # Excludes dotfiles
document.txt
downloads
  
$ ls -a      # Displays dotfiles with -a
.config
.ssh
document.txt  
downloads
  
$ ls --all   # Also shows dotfiles with long --all  
.config
.ssh     
document.txt
downloads

Here the single dash -a variant offers quick dotfile access, while --all makes the intent more explicit.

tar -xf vs tar –extract –file

The tar archiving program supports both single letter arguments and descriptive long options.

For example, extracting backup.tar uses either:

$ tar -xf backup.tar

Or:

 
$ tar --extract --file backup.tar

The first adheres to the short option Unix convention. But the second follows natural language parsing rules.

Common Pitfalls

Mixed use of the dash types can create several pitfalls:

• Assuming short vs long options are interoperable when they differ
• Forgetting meaning of obtuse single letter codes
• Supplying short options positionally when order matters
• Negating options incorrectly with capital letters

For example, take compressing with gzip. Enabling both recursion and keeping input files might expect:

$ gzip -r -k *.txt 

But the long options actually use “recursive” and “keep”, which fail:

  
$ gzip --recurse --keep *.txt
gzip: unrecognized option '--recurse'

So double check docs when mixing single and double dash arguments.

Best Practices

Some tips for effectively applying both dash types:

• Prefer double dash arguments for readability in scripts and automation
• Use single dash shorthand for iterative terminal work
• Document custom short options with comments
• Validate negation and chaining logic for single dashes
• Check man pages for available option styles

Also when writing new commands or scripts that accept options, offer both dash types to maximize usability.

Summary

The single dash “-” and double dash “–” enable a mixed command line syntax balancing brevity and explicitness in Linux. Single dashes serve an abbreviation role for common options. While double dashes provide self-documenting clarity especially for complex operations. Mastering both dash types unlocks the possibilities of Linux direction and control.