Bash

• Special Charactes
  • # Octothorp:
    1. Comment
    2. Pattern Matching
  • ; Semicolon: Command Separator
  • ;; Double Semicolon: Case Terminator
  • . Period/Dot
    1. Source
    2. Component of a file name
       1. Hidden file prefix
       2. Current directory
       3. Double dot: Parent Directory
    3. Character match: Match a single character
  • " Double quote: Partial quoting
  • ' Single quote: Full quoting
  • , Comma: Link aritithmetic operations
  • \ Back slash: escape
  • / Forward slash
    1. Path separator
    2. Arithmetic divide operator
  • ` Back tick: Command Substitution
  • : Colon: Null Command
  • * Asterisk
    1. Wild card: match all characters
    2. Pattern Matching: match zero or more
    3. Arithmetic: multiplication operator
    4. Double Asterisk: exponentiation operator
  • ? Test operator
    1. Double parenthesis context: trinary operator
    2. Parameter Substitution: test if variable set
    3. Wild card: match one character
    4. Pattern matching: represent one character
  • $ Dollar Sign
    1. Variable substitution: $a
    2. Regular Expression: Match end-of-line
    3. ${} See: Parameter Substitution
    4. Postitional Parameters: $*, $@
    5. Exit status: $?
    6. Process ID; $$
  • () Parenthesis
    1. Command group (a='hello'; echo $a): starts a subshell
    2. Array initialization array_a=(elem1 elem2 elem3)
  • {} Braces
    1. Brace Expansion: cat {file1,file2,file3} > combined_file
    2. Extended Brace Expansion: echo {a..z} --> echos chars from a to z
    3. Code block: anonymous function
    4. Text place holder: ls . | xargs -i -t cp ./{} $1
    5. Path name: find . -type f -exec file '{}' \; (semi-colon ends -exec option and must be escaped)
  • [ ] Brackets
    1. [ ] Test
    2. [[ ]] Test
    3. Array element: ${array_a[0]}
    4. Regular expression: Character Range [a-z]
  • (( )) Integer expression
• Parameter Substitution

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	Many thanks to Debra Lynn and Ian Murdock for making Debian possible
	First created Apr 22, 2008 ~ Last revised September 06, 2009