Definitions

# $PATH
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# Add to beginning of $PATH
PATH=~/opt/bin:$PATH
​
# Add to end of $PATH
PATH=$PATH:~/opt/bin

# Standard input & output
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# Send output of command to a file instead of terminal
# Shell will create a file if it does not exist, if it does, the shell erases (clobbers) the original file first
command > file
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# Append to file
command >> file
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# Match every line that I type after that has 'this' in it and put the results in to hello_grep.txt file
grep this > hello_grep.txt
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# Put all the lines matching 'line' into grep_output.txt file
grep line hello.txt > grep_output.txt
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# >> Redirect output to append to FILE
grep line hello.txt >> grep_output.txt
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# Redirect standard error stream to FILE
# where 2> means redirect output stream 2 to write results to the
# file and not to the terminal
find / -name 'story.txt' 2> error_log.txt
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# 1> specifies stream ID 1 (standard output) (default)
# 2> specifies stream ID 2 (standard error)
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# Sends both standard error and output to some location
ls /fffff > f 2>&1

- Accept - Specifies the file format the requester wants.
- Accept-Language - Specifies the human-readable language, like English, Spanish, or Russian.
- Cache-Control - Specifies whether the response can be generated from a cache.

# Globbing
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# Shell can match simple patterns to file and directory names
# this process is known as globbing
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# Simplest of these is the glob character * which tells the shell to match any number of arbitrary characters
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# Print a list of files in current directory
echo *
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# Shell matches arguments containing globs to filenames
# substititutes the filenames for those arguments, and then runs the revised command line
# the substitution is called expansion because the shell substitutes all matching filenames
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at* # Expands to all filenames that start with at
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*at # Expands to all filenames that end with at
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*at* # Expands to all filenames that contain at
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# Another shell glob character is (?) - it instructs the shell to match exactly one arbitrary character
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# Match both boat and brat
b?at
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# If you don't want the shell to expand a glob in a command, enclose the glob in single quotes ('')
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# It is important to remember that the shell performs expansions before running commands

ASCII code
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- ASCII is an encoding representing each typed letter by a number
- each number is stored in one byte (so the number is in 0..255)
  - A is 65
  - B is 66
  - space is 32
- "Unicode" is an encoding for mandarin, greek, arabic, etc. languages
  - typically 2-bytes per "letter"
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![](https://i.imgur.com/qbFb4Ik.png)

HTTP status codes
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- 200-299 are good
- 300-399 understood (located elsewhere)
- 400-499 error (404 = resource no longer exists)
- 400-599 server end (500 = some error on the server)

HTTP REST methods
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- GET - Used for fetching either a collection of resources or a single resource.
- POST - Used to add a new resource to a collection.
  - For example, we wouldn't POST to /players/567 or /games/1234 because they aren't collections.
  - We would, however, POST to /players or /games to create a new player or a new game.
- PUT - Use when we want to update a record. We wouldn't use PUT on collection or list URLs.
- DELETE - Used for sending a DELETE request to a detail record, a URL for a single record, should delete just that record.
  - Sending DELETE to an entire collection would delete the whole collection but that's usually not implemented, with good reason.