More notes on CLI, circuits

- Streams, redirection, pipes, jobs
- Some parsed circuit notes from ECS 154A

docs/Public/Software/Computer Architecture/gate.md

@@ -0,0 +1,5 @@
+A *gate* is the building block of a computer, performing basic logical functions. [^1]
+
+They have multiple inputs, and produce one output. 
+
+[^1]: https://www.techtarget.com/whatis/definition/logic-gate-AND-OR-XOR-NOT-NAND-NOR-and-XNOR#:~:text=A%20logic%20gate%20is%20a,of%20logic%20gates%20in%20them.

docs/Public/Software/Computer Architecture/multiplexer.md

@@ -0,0 +1,7 @@
+A *multiplexer* selects one of its [[data]] ports to forward to the output based on the selection signal.
+
+It behaves like a switch statement in programming. 
+
+![[Mux.png]]
+
+In general, a *multiplexer* has $2^n$ data inputs and requires $n$ select bits to choose which one will be the output. Larger *multiplexers* can be constructed with [[gate]] and [[tree]] of other *multiplexers*. 

docs/Public/Software/Networks/SSH.md

@@ -2,4 +2,9 @@
 
 *SSH* is often used to "login" and perform operations on remote computers, but can also be used for transferring data. [^1]
 
+You can run a [[command]] on remote machines and [[pipe]] the result:
+```bash
+ssh [email protected] ls | grep Downloads
+```
+
 [^1]: https://www.ucl.ac.uk/isd/what-ssh-and-how-do-i-use-it

docs/Public/Software/Operating Systems/Bash cheat sheet.md

@@ -34,4 +34,54 @@ cp <flags> <sourcePath(s)> <destinationPath>
 rm <flags> <filePath(s)>
 ```
 - Remove each specified file permanently
-		- Does not remove directories by default
+		- Does not remove directories by default
+```bash
+alias <aliasName>='<commandToRun>'
+```
+- Substitutes the alias name with the command to be run
+	- Create shortcuts for tedious commands
+	- Extend the default behavior of commands
+```bash
+alias rm='rm -i'          # confirm to delete file
+alias rm='mv -t -/.tash'  # move file to a trash directory
+alias cp='cp -b'          # make backup of destinationFile
+alias mv='mv -u'          # move only if sourceFile is newer
+alias hello="echo 'cow power'"
+```
+
+```bash
+cat <flags> <file>
+less <flags> <file>
+```
+- Print contents of file to screen; concatenate
+	- `less` outputs a page at a time, to scroll through
+	- Can search through file using the `/<word>` 
+```bash
+head <flags> <file>
+```
+- Shows the first 10 lines of a file
+	- Use `-n <number of lines>` to print certain number of lines from file
+```bash
+tail <flags> <file>
+```
+- Shows the last 10 lines of a file
+```bash
+nano <flags> <file>
+```
+- Opens simple [[CLI]] text editor
+```bash
+vim <flags> <file>
+```
+- Another text editor
+```bash
+man <command>
+man mkdir
+man stdio
+```
+- System reference manuals
+- Contains details of all command behavior and flags
+- Documentation of c libraries
+```bash
+tldr <flags> <command>
+```
+- Lists the typical uses of a command

docs/Public/Software/Operating Systems/Bash.md

@@ -1,4 +1,4 @@
-*See:* [Advanced Bash-Scripting Guide](https://tldp.org/LDP/abs/html/)
+*See:* [Advanced Bash-Scripting Guide](https://tldp.org/LDP/abs/html/), [[Bash cheat sheet]]
 
 *Bash* is a [[shell]] that is widely used in [[Linux]] and [[MacOS]] as the default shell. [^1]
 

docs/Public/Software/Operating Systems/command.md

@@ -1,3 +1,29 @@
 A *command* is a request to perform an operation or run a program. 
 
-You can add a [[flag]] which affect how a *command* can work. 
+You can add a [[flag]] which affect how a *command* can work. 
+
+`;`:
+- Execute *commands* in series
+```bash
+echo -n "hello " ; echo "world"
+hello world
+```
+
+`&&`:
+- Conditionally on success
+```bash
+cat / && echo "world"
+cat: /: Is a directory
+cd ~/slides/ && du -sh Makefile
+4.0K  Makefile
+```
+
+`||`:
+- Conditionally on failure
+```bash
+cat / || echo "Cat failed"
+cat /: Is a directory
+Cat failed
+echo -n "hello" || echo "world"
+hello
+```

docs/Public/Software/Operating Systems/exit.md

@@ -0,0 +1,14 @@
+An *exit* occurs when the command finishes. 
+
+A `0` indicates success. Any other value indicates error. 
+
+```bash
+echo "Hello" > /dev/null
+echo $?
+0
+
+cat missing.txt
+cat: missing.txt: No such file or directory
+echo $?
+1
+```

docs/Public/Software/Operating Systems/file system.md

@@ -1 +1 @@
-A *file system* of an [[operating system]] generally has a [[tree]] data structure for [[file]] which branches from the [[root]] to different directories. 
+A *file system* of an [[operating system]] generally has a [[tree]] data structure for [[file]] which branches from the [[[knowledge-base/docs/Public/Software/Theory/root|root]] to different directories. 

docs/Public/Software/Operating Systems/flag.md

@@ -1,3 +1,11 @@
 A *flag* can be added to a command to affect how it works. 
 
-Flags are combinational and the order does not matter. 
+Flags are combinational and the order does not matter. 
+
+`-h`: Help
+
+`-V`: Version
+
+`-v`, `-vv`, `-vvv`, `--quiet`: Configurable verbosity level
+
+`-r`: Recursive

docs/Public/Software/Operating Systems/kernel.md

@@ -2,4 +2,17 @@ The *kernel* is a computer program that is at the core of a computer's [[operati
 
 The *kernel* interacts with the [[shell]] and other programs, as well as the computer's [[hardware]], including the [[processor]], [[memory]], and disk drives. [^1] 
 
+Kernel parameters can be accessed through a pseudo [[file system]] `/sys`
+```bash
+cat /sys/class/input/mouse0/device/name
+Logitech USB Optical Mouse
+cat /sys/class/hwmon/hwmon3/temp1_crit
+120000
+cat /sys/class/leds/input2::scrolllock/brightness
+0
+```
+- Some system variables can be changed on the fly
+```bash
+sudo bash -c "echo 1 > /sys/class/leds/input2::scrollock/brightness"
+```
 [^1]: https://www.linfo.org/kernel.html

docs/Public/Software/Operating Systems/path.md

@@ -0,0 +1,27 @@
+A *path* is a special variable used to find the executable of a program. The [[shell]] searches `$PATH` when you enter a [[command]]. 
+
+```bash
+which ls
+/usr/bin/ls
+echo $PATH
+/usr/local/sbin:/usr/local/bin:/usr/bin:/opt/cuda-10.1/bin:/usr/lib/jvm/default/bin ...
+echo $PATH | sed 's/:/\n/g'
+/usr/local/sbin
+/usr/local/bin
+/usr/bin
+/opt/cuda-10.1/bin
+/usr/lib/jvm/default/bin
+```
+- You can run a program without searching for its path
+```bash
+./hello
+Hello World!
+```
+
+```bash
+hello
+bash: hello: command not found
+sudo mv hello/usr/local/bin
+hello
+Hello World!
+```

docs/Public/Software/Operating Systems/pipe.md

@@ -0,0 +1,10 @@
+A *pipe* is used to combine two or more commands. It will take the output of a [[command]] and use that as the input for the next command. [^1]
+
+Using the *pipe* '|' character: 
+```bash
+ls -l / | tail -n3
+```
+
+You can chain *pipes* together. 
+
+[^1]: https://www.redhat.com/sysadmin/pipes-command-line-linux

docs/Public/Software/Operating Systems/process.md

@@ -2,4 +2,68 @@ A *process* is a program or [[command]] that is actually running on the computer
 
 The [[operating system]] can run many different processes at the same time. [^1]
 
+*Process* commands on the [[CLI]]:
+
+`Ctrl+C`:
+- Stops a process
+```bash
+sleep 60
+^C
+```
+
+`Ctrl+Z`:
+- Pause a process
+```bash
+sleep 5
+^Z
+[1]+ Stopped          sleep 5
+echo "Hello"
+Hello
+```
+
+`fg`, `bg`:
+- Resume in either foreground or background
+```bash
+fg
+sleep 5
+```
+
+```bash
+bg
+[1]+ sleep 5 &
+echo "What now?"
+What now?
+[1]+   Done           sleep 5
+```
+
+`&`:
+- Start a process in the background
+```bash
+cat /dev/random > /dev/null &
+```
+
+`jobs`:
+- Lists all jobs (processes)
+```bash
+jobs
+[1]-   Stopped                   cat /dev/random > /dev/null
+[2]+   Stopped                   sleep 10
+```
+
+`kill`:
+- Terminate jobs (processes)
+```bash
+kill %1
+[1]+   Terminated                cat /dev/random > /dev/null
+```
+
+- Jobs are tied to the [[terminal]] session
+	- Exiting terminal kills stopped and backgrounded jobs
+
+- Protect background job from terminal exit:
+```bash
+nohup sleep 10 &           // "no hang up" for a new job
+disown %1                  // For a job already running
+```
+
 [^1]: https://www.ibm.com/docs/pt-br/aix/7.1?topic=administration-commands-processes

docs/Public/Software/Operating Systems/redirection.md

@@ -0,0 +1,21 @@
+*See: * [[stream]]
+
+A *redirection* is a way to change the standard input / output of the [[CLI]] to point to and from files. [^1]
+You can redirect `stdout` to a file like this:
+```bash
+echo "Hello World!" > hello.txt
+cat hello.txt
+```
+
+Redirect `stdin`: 
+```bash
+cat < hello.txt
+```
+
+Append `stdout` to a file:
+```bash
+cat < hello.text >> hello_copy.txt
+```
+
+
+[^1]: https://www.guru99.com/linux-redirection.html

docs/Public/Software/Operating Systems/root.md

@@ -0,0 +1,9 @@
+*Root* is a user account for administrative purposes, and typically has the highest access rights on the system. [^1]
+
+You can use `sudo` to perform actions as *root*.
+- Short for "super user do"
+- Actions run as root can damage your system
+
+Some things do require *root* privileges, if they change any files in the *root*. 
+
+[^1]: https://www.ssh.com/academy/pam/root-user-account#:~:text=Root%20is%20the%20superuser%20account,account%2C%20regardless%20of%20the%20name.

docs/Public/Software/Operating Systems/stream cheat sheet.md

@@ -0,0 +1,62 @@
+*See:* [[stream]]
+`head`:
+- Sends the first `n` lines of its input to its output
+```bash
+head -n3
+```
+
+`tail`: 
+- Sends the last `n` lines of its input to its output
+```bash
+tail -n3
+```
+
+```bash
+ls -l / > temp.txt
+tail -n3 < temp.txt
+```
+
+`grep`: 
+- Searches the input stream for a string
+- Outputs every line that contains the string
+```bash
+history | grep tail
+```
+
+`cut`:
+- Removes sections from each line of the input
+- Useful when filtering columns from input
+```bash
+cat foo.txt
+A,B,C,D
+A,B,C,D
+B,B,C,D
+D,C,B,A
+cat foo.txt | cut -d "," -f1,4
+A,D
+B,D
+D,A
+```
+
+`sort`:
+- Sorts the input and sends it to `stdout`
+- Defaults to alphanumeric sort, but it has many sorting options
+
+`uniq`:
+- Outputs the unique lines in the input
+- Only detects repeated lines if they are adjacent
+	- Input needs to be sorted first
+```bash
+sort foo.txt | uniq     // Display each line once
+sort foo.txt | uniq -u  // Display only unique lines
+sort foo.txt | uniq -d  // Display only duplicated lines
+sort foo.txt | uniq -c  // Display frequency of each line
+```
+
+`tee`:
+- Read from standard input and write to standard output and files
+```bash
+echo 1 | sudo tee /sys/class/leds/input2::scrolllock/brightness
+```
+
+

docs/Public/Software/Operating Systems/stream.md

@@ -0,0 +1,7 @@
+*See:* [[stream cheat sheet]]
+
+A *stream* refers to a collection of text. 
+
+There are generally two *streams* in the command line: 
+- `stdin` for user input (default is keyboard)
+- `stdout` for user output (default is display)

docs/Public/Software/Operating Systems/text editor.md

@@ -0,0 +1,3 @@
+A *text editor* is a program that edits plain text. They are sometimes known as "notepad" software. [^1]
+
+[^1]: https://en.wikipedia.org/wiki/Text_editor