Linux on maladroit.dev

alias

Mon, 01 Jan 0001 00:00:00 +0000

alias

Creating an alias for complex commands

alias workspace=cd ~/workspace

References

Command-Line-A-modern-introduction

cd

Mon, 01 Jan 0001 00:00:00 +0000

cd

Change directory. Works with the Directory path special characters

# navigates to the workspace directory
cd ~/workspace

# navigates to the previous directory
cd -

References

Command-Line-A-modern-introduction

Command line arguments

Mon, 01 Jan 0001 00:00:00 +0000

Command line arguments

Command line arguments are passed to command line applications and come in two varieties.

Positional arguments

Positional arguments can be any number of arguments that are separated by a space. If an argument contains a space in it, it must either be escaped or surrounded with quotes

cd ~/workspace

# Escaping whitespace
cd ~/workspace/ian\ weller
cd "~/workspace/ian weller"

# This is technically two positional arguments being passed
echo Hello World

Optional arguments

Arguments that are either prefixed with the short-form - or the long-form --. Optional arguments usually change the functionality of the command they are passed to. Short-form optional arguments can be separated out or combined.

Command Line Interface

Mon, 01 Jan 0001 00:00:00 +0000

Command Line Interface

A terminal used for interacting with an operating system. CLI applications can be very useful for a variety of reasons:

Interact with head-less servers
String multiple commands together using STDIN and STDOUT
Can be automated using scripting or schedulers
Easy to write

References

Command-Line-A-modern-introduction

Command substitution

Mon, 01 Jan 0001 00:00:00 +0000

Command-substitution

Command substitution replaces itself with the internal command.

python script.py --secret_key "$(cat ~/.secret_key)"

Alternatively, process substitution can be used to instead create a temporary file with the contents of the command, and then return the file path.

python script.py --file <(python generate_key.py)

References

Command-Line-A-modern-introduction

Special character	Description
/	Root path
.	Symlink to current directory
..	Symlink to the parent directory
~	User directory
~iweller	The user directory for iweller

Directories	Description
/bin	binary programs
/etc	system configuration files
/home	home directory for users on the machine
/opt	third party software
/tmp	temporary space, cleared on reboot
/usr	user related programs
/var	log files

File

Mon, 01 Jan 0001 00:00:00 +0000

File

In Linux, everything is considered a file. General files can be anything from text, audio, pictures, etc. These can be in text or binary format. Additionally there are Directory files that serve as containers for other files. Finally device files are any IO devices connected to the computer such as disks, keyboards, etc.

References

Command-Line-A-modern-introduction

git

Mon, 01 Jan 0001 00:00:00 +0000

git

worktrees

git config remote.origin.fetch "+refs/heads/*:refs/remotes/origin/*"

References

jq manual

GUI

Mon, 01 Jan 0001 00:00:00 +0000

Graphical-User-Interface

A graphical Shell

References

Command-Line-A-modern-introduction

history

Mon, 01 Jan 0001 00:00:00 +0000

history

History views the history of previously executed commands. Commands are kept in the $HISTFILE and are not updated until the user logs out. Updating the $HISTFILE can be forced using the command history -w.

Reuse commands

Previously executed commands can be replayed using the ! operator. This can work for both commands or specifying command parameters.

docker-compose -f ~/special-file.yml up -d

# replay the last command
!!

# replay specific command with last seen arguments
!docker-compose

Hiding from history

Adding a space to the front of any command will prevent it from being written to the $HISTFILE.

jq

Mon, 01 Jan 0001 00:00:00 +0000

jq

jq is a command line tool for processing JSON. It is a single binary, written in C, and has no runtime dependencies. This allows jq to be very fast, reliable, consistent across all machines.

References

jq manual

Kernel

Mon, 01 Jan 0001 00:00:00 +0000

Kernel

Linux

Mon, 01 Jan 0001 00:00:00 +0000

Linux

Logical operators

Mon, 01 Jan 0001 00:00:00 +0000

Logical-operators

Logical operators can be used as conditional logic for connecting commands together

Operator	Outcome
&&	Will run the next command if the first one succeeded
\|\|	Will run the next command if the first one failed
;	Will run both commands regardless of the outcome

References

Command-Line-A-modern-introduction

Programs

Mon, 01 Jan 0001 00:00:00 +0000

Programs

A program is a step by step procedure that is used for solving a computational problem. Programs are different from algorithms in that they are written during the Software implementation phase. A program must be written in a programming language and should be tested by the programmer.

pwd

Mon, 01 Jan 0001 00:00:00 +0000

pwd

pwd is print working directory.

pwd
# /home/maladroitthief/

The environment variables $PWD and $OLDPWD can be used to reference the current and previous working directory of the current session.

References

Command-Line-A-modern-introduction

Shell

Mon, 01 Jan 0001 00:00:00 +0000

Shell

A graphical or text interface used to interact with the operating system.

References

Command-Line-A-modern-introduction

Shell expansion

Mon, 01 Jan 0001 00:00:00 +0000

Shell-expansion

Shell expansions are shortcuts that can save a significant amount of time typing.

File globbing

Replacing a pattern in a file name or directory

Expansion	Description
~	Expansion for current home directory
*	Matches `0 TO n` characters
[ab]	Matches the characters `a OR b`
[0-9]	Matches characters in the sequence `0 TO 9`
[a-z]	Matches characters in the sequence `a TO z`
^	Negate the expansion: `^[ab]` is NOT a OR b
$	Match the end: `a$` is ends in `a`
(PATTERN1\|PATTERN2)	Match `PATTERN1 OR PATTERN2`

References

Command-Line-A-modern-introduction

Shell script

Mon, 01 Jan 0001 00:00:00 +0000

Shell script

Template

#!/usr/bin/env bash

set -o errexit
set -o nounset
set -o pipefail
if [[ "${TRACE-0}" == "1" ]]; then
	set -o xtrace
fi

if [[ "${1-}" =~ ^-*h(elp)?$ ]]; then
 echo 'Usage: ./script.sh arg-one arg-two

This is an awesome bash script to make your life better.

'
 exit
fi

cd "$(dirname "$0")"

main() {
 echo do awesome stuff
}

main "$@"

Shell variables

Mon, 01 Jan 0001 00:00:00 +0000

Shell-variables

Shell variables are variables that are only applied to the current shell instance.

var=TestVar
echo $var
echo ${var} # long format for expressions in strings

Environment variables

Environment variables are shell variables that are inherited by all system processes. A shell variable can be promoted to an environment variable by exporting it.

export var=TestVar

All current environment variables can be viewed using export

References

Command-Line-A-modern-introduction

Standard streams

Mon, 01 Jan 0001 00:00:00 +0000

Standard-streams

Standard in, out, and error streams created when a command is run. They are usefully for passing data between applications. Most CLI applications support using stdin as in input and will create both stdout and stderr outputs, allowing multiple commands to be chained together.

The streams behave like files and are given the following descriptors:

stdin: 0
stdout: 1
stderr: 2

These streams can be redirected using > or >> where > overwrites the file and >> appends to the end. To redirect a specific stream, prepend the operators with the stream descriptor.

tee

Mon, 01 Jan 0001 00:00:00 +0000

tee

The tee command reads from stdin and writes to both stdout and one or more files.

df -h | tee disk_usage.txt

References

Command-Line-A-modern-introduction

Terminal

Mon, 01 Jan 0001 00:00:00 +0000

Terminal

A text based shell.

References

Command-Line-A-modern-introduction

xargs

Mon, 01 Jan 0001 00:00:00 +0000

xargs

The xargs command will run a command multiple times.

# Remove all .png files in the currect directory
find . -name "*.png" | xargs rm -rf

References

Command-Line-A-modern-introduction

Linux on maladroit.dev

alias

alias

References

cd

cd

References

Command line arguments

Command line arguments

Positional arguments

Optional arguments

Command Line Interface

Command Line Interface

References

Command substitution

Command-substitution

References

Directory

Directory

Path special characters

Top level directories

References

File

File

References

git

git

worktrees

References

GUI

Graphical-User-Interface

References

history

history

Reuse commands

Hiding from history

jq

jq

References

Kernel

Kernel

Linux

Linux

Logical operators

Logical-operators

References

Programs

Programs

pwd

pwd

Related

References

Shell

Shell

References

Shell expansion

Shell-expansion

File globbing

References

Shell script

Shell script

Template

Shell variables

Shell-variables

Environment variables

References

Standard streams

Standard-streams

tee

tee

References

Terminal

Terminal

References

xargs

xargs

References