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Bash

Notes for Professionals

Bash

Notes for Professionals

GoalKicker.com

Free Programming Books

Disclaimer

This is an unocial free book created for educational purposes and is

not aliated with ocial Bash group(s) or company(s).

All trademarks and registered trademarks are

the property of their respective owners

100+ pages

of professional hints and tricks

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 .........................................................................................................................................

Section 22.2: String comparison and matching 83 .......................................................................................................

Section 22.3: Test on exit status of a command 85 ......................................................................................................

Section 22.4: One liner test 85 .........................................................................................................................................

Section 22.5: File comparison 85 ....................................................................................................................................

Section 22.6: File access tests 86 ....................................................................................................................................

Section 22.7: Numerical comparisons 86 .......................................................................................................................

Chapter 23: Scripting with Parameters 88 ...........................................................................................................

Section 23.1: Multiple Parameter Parsing 88 ..................................................................................................................

Section 23.2: Argument parsing using a for loop 89 ....................................................................................................

Section 23.3: Wrapper script 89 ......................................................................................................................................

Section 23.4: Accessing Parameters 90 .........................................................................................................................

Section 23.5: Split string into an array in Bash 91 .........................................................................................................

Chapter 24: Bash history substitutions 92 ...........................................................................................................

Section 24.1: Quick Reference 92 ....................................................................................................................................

Section 24.2: Repeat previous command with sudo 93 ...............................................................................................

Section 24.3: Search in the command history by pattern 93 .......................................................................................

Section 24.4: Switch to newly created directory with !#:N 93 ......................................................................................

Section 24.5: Using !$ 94 ..................................................................................................................................................

Section 24.6: Repeat the previous command with a substitution 94 ..........................................................................

Chapter 25: Math 95 ........................................................................................................................................................

Section 25.1: Math using dc 95 ........................................................................................................................................

Section 25.2: Math using bash capabilities 96 ...............................................................................................................

Section 25.3: Math using bc 96 ........................................................................................................................................

Section 25.4: Math using expr 97 ....................................................................................................................................

Chapter 26: Bash Arithmetic 98 .................................................................................................................................

Section 26.1: Simple arithmetic with (( )) 98 ...................................................................................................................

Section 26.2: Arithmetic command 98 ...........................................................................................................................

Section 26.3: Simple arithmetic with expr 99 .................................................................................................................

Chapter 27: Scoping 100 ................................................................................................................................................

Section 27.1: Dynamic scoping in action 100 .................................................................................................................

Chapter 28: Process substitution 101 ......................................................................................................................

Section 28.1: Compare two ﬁles from the web 101 .......................................................................................................

Section 28.2: Feed a while loop with the output of a command 101 ..........................................................................

Section 28.3: Concatenating ﬁles 101 ............................................................................................................................

Section 28.4: Stream a ﬁle through multiple programs at once 101 ..........................................................................

Section 28.5: With paste command 102 ........................................................................................................................

Section 28.6: To avoid usage of a sub-shell 102 ...........................................................................................................

Chapter 29: Programmable completion 103 .......................................................................................................

Section 29.1: Simple completion using function 103 .....................................................................................................

Section 29.2: Simple completion for options and ﬁlenames 103 ................................................................................

Chapter 30: Customizing PS1 104 ..............................................................................................................................

Section 30.1: Colorize and customize terminal prompt 104 .........................................................................................

Section 30.2: Show git branch name in terminal prompt 105 .....................................................................................

Section 30.3: Show time in terminal prompt 105 ...........................................................................................................

Section 30.4: Show a git branch using PROMPT_COMMAND 106 ..............................................................................

Section 30.5: Change PS1 prompt 106 ............................................................................................................................

Section 30.6: Show previous command return status and time 107 ..........................................................................

Chapter 31: Brace Expansion 109 ...............................................................................................................................

Section 31.1: Modifying ﬁlename extension 109 .............................................................................................................