Command Line

Intro

Command line tools have NOT faded out into the past. They have kept consistently evolving and being improved. They still do! A lot of GUI interfaces use command line tools behind the scenes.

There exists a specification to standardize how command line utilities should behave so that they work in a cross-platform, interoperable way.

GNU and BSD command line utilities generally try to follow the specs but add the so called extensions which add further capabilities to the tools, making writing scripts and programs easier and sometimes less verbose, but also reduce the portability. Some tools can be run in a more restrict way that disallow extensions. The docs for each tool should specify those things. Information about these things is also scattered across this website’s notes and examples when they are deemed important and/or worthwhile.

Besides reading the specs, also take a look at the sidebar about reading and understanding man pages, info pages and help pages.

Note

Assume all text and examples on this site is written considering GNU tools and the Bash shell unless otherwise noted.

Single Unix Specification (SUS)

• XBD: Base Definitions

• XSH: System Interfaces and XBD Headers

• XCU: Shell and Utilities (Commands and Utilities)

More info on the link The Open Group Base Specifications Issue 7, 2018 edition. There is also a question about the difference between SUS and Open Group.

Yes, That Website Sucks

Yes, that website sucks. Not the contents of the website, but the way it works!

The whole thing is full of iframes. URLs don’t change (only the iframes contents do) when we click on sidebar links which means it is impossible to share or bookmark different URLs do. HOWEVER, if we open links on a new tab then we get out of the iframe hell thing. So, open links on a new tab when you need the URL for that link.

GNU Coreutils

Note

The examples on this site assume GNU tools and GNU Coreutils. If you find something that doesn’t work on your version/vendor of the tool, feel free to open a PR to this project proposing an alternative working solution.

It is worth taking a look at following resources:

• GNU Coreutils Home Page

• GNU Coreutils FAQ

• GNU Coreutils Documentation

• GNU Coreutils Decoded

There is also the mind-blowing, awesome Decoded GNU Coreutils project by MaiZure.

Command Line:

• Man, Info and Help
  • help
  • info
    • info summary
  • man
    • Finding Info Node Names
  • `cp’ Man Page Example
  • `csi’ -help Example
  • Command Options
  • POSIX and GNU
  • Documentation Relationships
    • End of Options echo Example
  • Other Links and Resources
• Shell Built-In Commands
  • Intro
  • POSIX builtin reserved word
  • Shells implementation of builtin
• Shell Argument Syntax
  • Whitespace and Quoting
    • A Sad rm Incident
  • End Of Options ‘--’
    • remove files starting with ‘-’
• echo and printf
  • Intro
  • echo
    • echo and newline
    • How to print ‘-n’?
    • Prefer printf instead of echo
  • printf
    • Format operand reutilization
• Redirections
  • cat STDIN and redirect to file
• Bash Brace Expansion
  • Moving (renaming) files
• Bash Parameter Expansion
  • remove newline
• Bash Aliases
  • Intro
  • How To Unalias‽
  • Manually Expanding Aliases
  • Tricky aliases 😮
• Bash Arrays
  • Serialize and Store Bash Array to a File
  • Deserialize Bash Array From a File
    • Using mapfile
    • Why can’t we use read‽
    • Understanding mapfile vs read
    • IFS= and \0
    • field separator vs terminator
  • Serialize a NUL-separated list of files to a variable
• Terminal Emulators
  • Kitty
    • Login Shell and Startup RC Files
    • Single vs Multiple Kitty Windows
    • Setting Title
    • Themes
      • Vim + Kitty + Solarized Light
  • Indices and tables
• tar | Command Line
  • Pack Excluding Directories
• Useful find examples
  • Find files and store in array
• HackerRank Shell
  • Intro
  • Easy Challenges
    • Let’s Echo
    • Looping With Numbers
    • Looping And Skipping
    • A Personalized Echo
    • The World of Numbers
    • Getting started with conditionals
    • More on Conditionals
    • Arithmetic Operations
    • Compute the Average
    • cut Challenges
    • Head of Text File Challenges
    • Middle of a Text File
    • Tail of a Text File 1 and 2
    • tr Command 1
    • tr Command 2
    • tr Command 3
    • sort Lines Challenges
    • uniq Challenges
    • Read In An Array
    • Display an Element of an Array
    • Count Elements in an Array
    • Slice An Array
    • Concatenate Array With Itself
    • grep A
    • grep B
    • sed 3
    • sed 4
  • Medium Challenges
    • Paste 1
    • paste 2
    • paste 3
    • paste 4
    • sed 1
    • sed 2
    • grep challenges
    • awk challenges
    • Filter an Array With Patterns
    • Remove First Capital Letter From Each Array Element
  • Hard Challenges
    • sed 5
    • Lonely Integer
    • Fractal Tree
  • The End