Wildcards (Globbing Patterns)
--
*	Matches any string of characters (including an empty string). #ls *.txt
?	Matches any single character. #ls file?.txt
[ ]	Matches any one of the enclosed characters. Can also specify a range. #ls file[1-3].txt
[^ ]	Matches any character not enclosed.
[! ]	Matches any character not enclosed. # ls file[!0-9].txt


Redirection Symbols
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>	Redirects standard output to a file, overwriting the file. #echo "Hello" > file.txt  # Writes "Hello" to file.txt
>>	Redirects standard output to a file, appending to the file.
<	Redirects standard input from a file.
2>	Redirects standard error to a file. # ls non_existing_file 2> error.log
2>>	Appends standard error to a file.
&>	Redirects both standard output and standard error to a file (not POSIX standard, but commonly supported).
>&	Redirects standard output to standard error.
|	Sends the output of one command as input to another command.


Quoting
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"	Double quotes, preserves the literal value of all characters within the quotes, except for $, \, and `# echo "Hello $USER"  # Expands $USER
'	Single quotes, preserves the literal value of all characters within the quotes.#echo 'Hello $USER'  # Does not expand $USER
`	Backticks, command substitution, captures the output of a command.
$()	Command substitution, alternative to backticks.

Logical Operators
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&&	Logical AND, executes the second command only if the first one succeeds.# mkdir new_dir && cd new_dir  # Creates and then enters new_dir if successful
||	Logical OR, executes the second command only if the first one fails.# cd non_existing_dir || echo "Directory does not exist"  # Outputs a message if cd fails
!	Logical NOT, negates the exit status of a command. if ! grep -q "search_term" file.txt; then

Grouping
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( )	Groups commands to be executed in a subshell.# (cd /tmp && ls)  # Changes to /tmp and lists files there, without affecting the current shell
{ }	Groups commands to be executed in the current shell.# { echo "Hello"; echo "World"; } > file.txt  # Writes both strings to file.txt

Escape Characters
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\	Escape character, used to escape the following character.# echo "A quote: \"Hello\""  # Outputs: A quote: "Hello"

Miscellaneous
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#	Comment, everything after # on the same line is ignored.
;	Command separator, allows multiple commands on one line.# echo "Hello"; echo "World"  # Outputs: Hello World
&	Background operator, runs the command in the background. #sleep 10 &  # Runs sleep command in the background
$	Variable prefix, used to reference the value of a variable.