Popular Bash Notes for Professionals

Bash
Bash
Notes for Professionals




Notes for Professionals




100+ pages
of professional hints and tricks


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,Contents
About ................................................................................................................................................................................... 1
Chapter 1: Getting started with Bash ................................................................................................................. 2
Section 1.1: Hello World ................................................................................................................................................. 2
Section 1.2: Hello World Using Variables ..................................................................................................................... 4
Section 1.3: Hello World with User Input ...................................................................................................................... 4
Section 1.4: Importance of Quoting in Strings ............................................................................................................ 5
Section 1.5: Viewing information for Bash built-ins .................................................................................................... 6
Section 1.6: Hello World in "Debug" mode .................................................................................................................. 6
Section 1.7: Handling Named Arguments .................................................................................................................... 7
Chapter 2: Script shebang ........................................................................................................................................ 8
Section 2.1: Env shebang .............................................................................................................................................. 8
Section 2.2: Direct shebang .......................................................................................................................................... 8
Section 2.3: Other shebangs ........................................................................................................................................ 8
Chapter 3: Navigating directories ...................................................................................................................... 10
Section 3.1: Absolute vs relative directories .............................................................................................................. 10
Section 3.2: Change to the last directory .................................................................................................................. 10
Section 3.3: Change to the home directory .............................................................................................................. 10
Section 3.4: Change to the Directory of the Script .................................................................................................. 10
Chapter 4: Listing Files ............................................................................................................................................ 12
Section 4.1: List Files in a Long Listing Format ......................................................................................................... 12
Section 4.2: List the Ten Most Recently Modified Files ............................................................................................ 13
Section 4.3: List All Files Including Dotfiles ................................................................................................................ 13
Section 4.4: List Files Without Using `ls` ..................................................................................................................... 13
Section 4.5: List Files ................................................................................................................................................... 14
Section 4.6: List Files in a Tree-Like Format ............................................................................................................. 14
Section 4.7: List Files Sorted by Size .......................................................................................................................... 14
Chapter 5: Using cat .................................................................................................................................................. 16
Section 5.1: Concatenate files ..................................................................................................................................... 16
Section 5.2: Printing the Contents of a File ............................................................................................................... 16
Section 5.3: Write to a file ........................................................................................................................................... 17
Section 5.4: Show non printable characters ............................................................................................................. 17
Section 5.5: Read from standard input ..................................................................................................................... 18
Section 5.6: Display line numbers with output ......................................................................................................... 18
Section 5.7: Concatenate gzipped files ..................................................................................................................... 18
Chapter 6: Grep ........................................................................................................................................................... 20
Section 6.1: How to search a file for a pattern ......................................................................................................... 20
Chapter 7: Aliasing ..................................................................................................................................................... 21
Section 7.1: Bypass an alias ........................................................................................................................................ 21
Section 7.2: Create an Alias ........................................................................................................................................ 21
Section 7.3: Remove an alias ..................................................................................................................................... 21
Section 7.4: The BASH_ALIASES is an internal bash assoc array .......................................................................... 22
Section 7.5: Expand alias ............................................................................................................................................ 22
Section 7.6: List all Aliases .......................................................................................................................................... 22
Chapter 8: Jobs and Processes ........................................................................................................................... 23
Section 8.1: Job handling ............................................................................................................................................ 23
Section 8.2: Check which process running on specific port .................................................................................... 25

, Section 8.3: Disowning background job .................................................................................................................... 25
Section 8.4: List Current Jobs ..................................................................................................................................... 25
Section 8.5: Finding information about a running process ..................................................................................... 25
Section 8.6: List all processes ..................................................................................................................................... 26
Chapter 9: Redirection ............................................................................................................................................. 27
Section 9.1: Redirecting standard output .................................................................................................................. 27
Section 9.2: Append vs Truncate ............................................................................................................................... 27
Section 9.3: Redirecting both STDOUT and STDERR .............................................................................................. 28
Section 9.4: Using named pipes ................................................................................................................................. 28
Section 9.5: Redirection to network addresses ........................................................................................................ 30
Section 9.6: Print error messages to stderr .............................................................................................................. 30
Section 9.7: Redirecting multiple commands to the same file ............................................................................... 31
Section 9.8: Redirecting STDIN .................................................................................................................................. 31
Section 9.9: Redirecting STDERR ............................................................................................................................... 32
Section 9.10: STDIN, STDOUT and STDERR explained ............................................................................................ 32
Chapter 10: Control Structures ............................................................................................................................ 34
Section 10.1: Conditional execution of command lists ............................................................................................. 34
Section 10.2: If statement ............................................................................................................................................ 35
Section 10.3: Looping over an array .......................................................................................................................... 36
Section 10.4: Using For Loop to List Iterate Over Numbers .................................................................................... 37
Section 10.5: continue and break ............................................................................................................................... 37
Section 10.6: Loop break ............................................................................................................................................. 37
Section 10.7: While Loop ............................................................................................................................................. 38
Section 10.8: For Loop with C-style syntax ............................................................................................................... 39
Section 10.9: Until Loop ............................................................................................................................................... 39
Section 10.10: Switch statement with case ................................................................................................................ 39
Section 10.11: For Loop without a list-of-words parameter ..................................................................................... 40
Chapter 11: true, false and : commands .......................................................................................................... 41
Section 11.1: Infinite Loop ............................................................................................................................................. 41
Section 11.2: Function Return ...................................................................................................................................... 41
Section 11.3: Code that will always/never be executed ........................................................................................... 41
Chapter 12: Arrays ...................................................................................................................................................... 42
Section 12.1: Array Assignments ................................................................................................................................. 42
Section 12.2: Accessing Array Elements .................................................................................................................... 43
Section 12.3: Array Modification ................................................................................................................................. 43
Section 12.4: Array Iteration ....................................................................................................................................... 44
Section 12.5: Array Length .......................................................................................................................................... 45
Section 12.6: Associative Arrays ................................................................................................................................. 45
Section 12.7: Looping through an array .................................................................................................................... 46
Section 12.8: Destroy, Delete, or Unset an Array ..................................................................................................... 47
Section 12.9: Array from string ................................................................................................................................... 47
Section 12.10: List of initialized indexes ...................................................................................................................... 47
Section 12.11: Reading an entire file into an array .................................................................................................... 48
Section 12.12: Array insert function ............................................................................................................................ 48
Chapter 13: Associative arrays ............................................................................................................................ 50
Section 13.1: Examining assoc arrays ........................................................................................................................ 50
Chapter 14: Functions ............................................................................................................................................... 52
Section 14.1: Functions with arguments ..................................................................................................................... 52
Section 14.2: Simple Function ..................................................................................................................................... 53
Section 14.3: Handling flags and optional parameters ........................................................................................... 53

, Section 14.4: Print the function definition .................................................................................................................. 54
Section 14.5: A function that accepts named parameters ...................................................................................... 54
Section 14.6: Return value from a function ............................................................................................................... 55
Section 14.7: The exit code of a function is the exit code of its last command ..................................................... 55
Chapter 15: Bash Parameter Expansion .......................................................................................................... 57
Section 15.1: Modifying the case of alphabetic characters ..................................................................................... 57
Section 15.2: Length of parameter ............................................................................................................................ 57
Section 15.3: Replace pattern in string ...................................................................................................................... 58
Section 15.4: Substrings and subarrays .................................................................................................................... 59
Section 15.5: Delete a pattern from the beginning of a string ................................................................................ 60
Section 15.6: Parameter indirection ........................................................................................................................... 61
Section 15.7: Parameter expansion and filenames .................................................................................................. 61
Section 15.8: Default value substitution ..................................................................................................................... 62
Section 15.9: Delete a pattern from the end of a string .......................................................................................... 62
Section 15.10: Munging during expansion ................................................................................................................. 63
Section 15.11: Error if variable is empty or unset ...................................................................................................... 64
Chapter 16: Copying (cp) ......................................................................................................................................... 65
Section 16.1: Copy a single file .................................................................................................................................... 65
Section 16.2: Copy folders ........................................................................................................................................... 65
Chapter 17: Find ........................................................................................................................................................... 66
Section 17.1: Searching for a file by name or extension .......................................................................................... 66
Section 17.2: Executing commands against a found file ......................................................................................... 66
Section 17.3: Finding file by access / modification time .......................................................................................... 67
Section 17.4: Finding files according to size .............................................................................................................. 68
Section 17.5: Filter the path ......................................................................................................................................... 69
Section 17.6: Finding files by type .............................................................................................................................. 70
Section 17.7: Finding files by specific extension ........................................................................................................ 70
Chapter 18: Using sort .............................................................................................................................................. 71
Section 18.1: Sort command output ........................................................................................................................... 71
Section 18.2: Make output unique .............................................................................................................................. 71
Section 18.3: Numeric sort .......................................................................................................................................... 71
Section 18.4: Sort by keys ........................................................................................................................................... 72
Chapter 19: Sourcing ................................................................................................................................................. 74
Section 19.1: Sourcing a file ......................................................................................................................................... 74
Section 19.2: Sourcing a virtual environment ........................................................................................................... 74
Chapter 20: Here documents and here strings ........................................................................................... 76
Section 20.1: Execute command with here document ............................................................................................. 76
Section 20.2: Indenting here documents .................................................................................................................. 76
Section 20.3: Create a file ........................................................................................................................................... 77
Section 20.4: Here strings ........................................................................................................................................... 77
Section 20.5: Run several commands with sudo ..................................................................................................... 78
Section 20.6: Limit Strings .......................................................................................................................................... 78
Chapter 21: Quoting ................................................................................................................................................... 80
Section 21.1: Double quotes for variable and command substitution .................................................................... 80
Section 21.2: Dierence between double quote and single quote ......................................................................... 80
Section 21.3: Newlines and control characters ......................................................................................................... 81
Section 21.4: Quoting literal text ................................................................................................................................. 81
Chapter 22: Conditional Expressions ................................................................................................................ 83
Section 22.1: File type tests ......................................................................................................................................... 83