Command Line

#Summary

Command line interfaces are powerful, but have a steep learning curve. A GUI is friendlier, but usually doesn’t have as many options. You’ll often hear RTFM (Read the Fucking Manual), but in reality the manual is even hard to read for a beginner and can get pretty complex even for advanced use cases. Here’s some notes:

##Man Pages

Linux manual pages are docs on how to use a command. Run with man (e.g. man man to see what man does). If there’s a number after a command, that is the Man page section. Sections break down into:

(1) User Commands
(2) System Calls
(3) Library functions
(4) Devices
(5) File Formats
(6) Games and Amusements
(7) Conventions and Miscellany
(8) System Administration and Priveledged Commands
(L) Local - some programs install their man pages into this section instead of (1)
(N) TCL commands

For example, you might type in the man command, the section, and the command you’re looking up (man 1 grep).

##Synopsis

This will tell you how to use the command and what options are available. Here’s how to read them given this format:

utlity_name[-a][-b][-c option_argument][-d][-e][-foption_argument][operand...]

###Synopsis Summary

utility_name - The utility in this example (e.g. man, grep, cat)
After the utility name, we have options, option-arguments, and operands
options are the arguments that have a hyphen and single letters or digits (e.g. -a). Aka flags
option-argument is when an option is followed by an argument, (e.g. [-c option_argument])
operands are the arguments following the last options and option-arguments, (e.g. `[operand…])

####Synopsis Details

Options are usually listed in alphabetical order
When a utility has only a few permissible options, they are sometimes shown individually. Utilities with many flags generally show all of the individual flags (that do not take option-arguments) grouped. Here’s the two examples:

Example utility with only a few options:

utility_name [-abcDxyz][-p arg][operand]

Example utility with very complex arguments:

utility_name [options][operands]

####To space or not to space in option_argument

If the synopsis of a utility shows a space between an option and an option-argument (e.g. [-c option_argument]), a conforming application should use separate arguments for that option and its option-argument.

If a space is not shown (e.g. [-foption_argument]), then a conforming application won’t add a space (and will just place an option and its option-argument directly adjacent in the same argument string).

###[]

Square parameters mean that the stuff inside is optional.

[optional]
[-abcgln]

###{}

Braces with a list of comma separated values mean a limited list of choices.

{one,two,three}
{yes,no}

###<>

Less-than and greater-than symbols mean a mandatory parameter. Usually these values have embedded underscores (e.g. file_name)

<mandatory>
<file_name>

###bolded text or ‘typewriter’ font

If there is bolded text or the typewriter font on text, this means a literal command line input (e.g. man, grep). Type it in as is.

###italics

If there is italics, this means its a variable that you can replace.

###

Vertical bars | mean these are separate choices (mutually exclusive, cannot both be true). If there are mutually-exclusive options and operands, use multiple synopsis lines.

Example of a mutually exclusive utility_name appearing on multiple lines of the synopsis:

utility_name -d[-a][-c option_argument][operand...]
utility_name [-a][-b][operand...]

###…

Ellipses (...) mean that one or more occurences of an option or operand ar allowed.

utility_name -f option_argument...[operand...]
utility_name [-g option_argument]...[operand...]

Uhh what? So in the first example, each option_argument needs a -f in front and you can have multiple option_arguments.

##Commands

###apropros

apropos searches the descriptions for instances of a keyword.

`apropos search`

###whatis

whatis to display a short description from the manual page, if available.

`whatis grep`
# git-grep(1)              - Print lines matching a pattern
# grep(1), egrep(1), fgrep(1), zgrep(1), zegrep(1), zfgrep(1) - file pattern searcher

Command Line

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