Acknowledgments xi
Part I: The Linux Command Line 1
Chapter 1: Starting with Linux Shells 3
Investigating Linux 3
Looking into the Linux kernel 4
System memory management 5
Software program management 6
Hardware management 8
Filesystem management 8
The GNU utilities 9
The core GNU utilities 10
The shell 10
The Linux desktop environment 11
The X Window software 12
The KDE Plasma desktop 12
The GNOME desktop 13
Other desktops 15
Examining Linux Distributions 17
Core Linux distributions 18
Specialized Linux distributions 19
Summary 20
Chapter 2: Getting to the Shell 21
Reaching the Command Line 21
Console terminals 22
Graphical terminals 22
Accessing CLI via a Linux Console Terminal 23
Accessing CLI via Graphical Terminal Emulation 26
Using the GNOME Terminal Emulator 27
Accessing GNOME Terminal 27
The menu bar 32
Using the Konsole Terminal Emulator 36
Accessing Konsole 36
The menu bar 38
Using the xterm Terminal Emulator 42
Accessing xterm 43
Command-line parameters 44
Summary 45
Chapter 3: Basic Bash Shell Commands 47
Starting the Shell 47
Using the Shell Prompt 48
Interacting with the Bash Manual 49
Navigating the Filesystem 53
Looking at the Linux filesystem 53
Traversing directories 57
Using absolute directory references 57
Using relative directory references 59
Listing Files and Directories 60
Displaying a basic listing 61
Displaying a long listing 63
Filtering listing output 64
Handling Files 66
Creating files 66
Copying files 66
Using command-line completion 69
Linking files 69
Renaming files 71
Deleting files 73
Managing Directories 74
Creating directories 74
Deleting directories 75
Viewing File Contents 77
Viewing the file type 77
Viewing the whole file 78
Using the cat command 78
Using the more command 78
Using the less command 80
Viewing parts of a file 80
Using the tail command 80
Using the head command 82
Summary 82
Chapter 4: More Bash Shell Commands 85
Monitoring Programs 85
Peeking at the processes 85
Unix-style parameters 86
BSD-style parameters 89
The GNU long parameters 91
Real-time process monitoring 93
Stopping processes 95
The kill command 95
The pkill command 96
Monitoring Disk Space 96
Mounting media 97
The mount command 97
The umount command 99
Using the df command 100
Using the du command 101
Working with Data Files 102
Sorting data 102
Searching for data 106
Compressing data 108
Archiving data 109
Summary 111
Chapter 5: Understanding the Shell 113
Investigating Shell Types 113
Exploring Parent and Child Shell Relationships 117
Looking at process lists 121
Creatively using subshells 123
Investigating background mode 123
Putting process lists into the background 125
Looking at co-processing 126
Understanding External and Built-In Commands 127
Looking at external commands 128
Looking at built-in commands 129
Using the history command 130
Using command aliases 134
Summary 135
Chapter 6: Using Linux Environment Variables 137
Exploring Environment Variables 137
Looking at global environment variables 138
Looking at local environment variables 140
Setting User-Defined Variables 141
Setting local user-defined variables 141
Setting global environment variables 142
Removing Environment Variables 144
Uncovering Default Shell Environment Variables 145
Setting the PATH Environment Variable 150
Locating System Environment Variables 152
Understanding the login shell process 152
Viewing the /etc/profi le file 152
Viewing the $HOME startup files 156
Understanding the interactive shell process 157
Understanding the noninteractive shell process 158
Making environment variables persistent 159
Learning about Variable Arrays 159
Summary 161
Chapter 7: Understanding Linux File Permissions 163
Exploring Linux Security 163
The /etc/passwd file 164
The /etc/shadow file 165
Adding a new user 166
Removing a user 169
Modifying a user 169
usermod 170
passwd and chpasswd 170
chsh, chfn, and chage 171
Using Linux Groups 173
The /etc/group file 173
Creating new groups 174
Modifying groups 175
Decoding File Permissions 176
Using file permission symbols 176
Default file permissions 178
Changing Security Settings 179
Changing permissions 180
Changing ownership 181
Sharing Files 182
Access Control Lists 184
Summary 186
Chapter 8: Managing Filesystems 189
Exploring Linux Filesystems 189
Exploring the Linux filesystem evolution 190
Looking at the ext filesystem 190
Looking at the ext2 filesystem 190
Digging into journaling filesystems 191
Looking at the ext3 filesystem 191
Looking at the ext4 filesystem 191
Looking at the JFS filesystem 192
Looking at ReiserFS 192
Looking at XFS 192
Understanding the volume-managing filesystems 192
Looking at the ZFS filesystem 193
Looking at the Btrfs filesystem 193
Looking at the Stratis filesystem 193
Working with Filesystems 194
Creating partitions 194
Looking at the fdisk utility 194
Working with gdisk 197
The GNU parted command 198
Creating a filesystem 199
Checking and repairing a filesystem 201
Managing Logical Volumes 202
Exploring LVM layout 203
Physical volume 203
Volume group 203
Logical volume 203
Understanding the LVM in Linux 203
Create the PVs 204
Create a VG 204
Create an LV 205
Using the Linux LVM 206
Format and mount an LV 206
Growing or shrinking your VGs and LVs 206
Summary 207
Chapter 9: Installing Software 209
Exploring Package Management 209
Inspecting the Debian-Based Systems 210
Managing packages with apt 211
Installing software packages with apt 213
Upgrading software with apt 215
Uninstalling software with apt 216
The apt repositories 218
The Red Hat–Based Systems 220
Listing installed packages 220
Installing software with dnf 221
Upgrading software with dnf 223
Uninstalling software with dnf 223
Dealing with broken dependencies 223
RPM repositories 224
Managing Software Using Containers 225
Using snap containers 225
Using flatpak containers 227
Installing from Source Code 229
Summary 232
Chapter 10: Working with Editors 235
Visiting the vim Editor 235
Checking your vim package 236
Exploring vim basics 237
Editing data 240
Copying and pasting 240
Searching and substituting 241
Navigating the nano Editor 242
Exploring the Emacs Editor 244
Checking your Emacs package 245
Using Emacs on the console 246
Exploring the basics of Emacs 247
Editing data 248
Copying and pasting 249
Searching and replacing 249
Using buffers in Emacs 250
Using windows in console mode Emacs 251
Using Emacs in a GUI 252
Exploring the KDE Family of Editors 253
Looking at the KWrite editor 253
Looking at the Kate editor 259
Exploring the GNOME Editor 263
Starting gedit 264
Understanding basic gedit features 265
Managing plugins 268
Summary 271
Part II: Shell Scripting Basics 273
Chapter 11: Basic Script Building 275
Using Multiple Commands 275
Creating a Script File 276
Displaying Messages 278
Using Variables 279
Environment variables 280
User variables 281
Command substitution 283
Redirecting Input and Output 284
Output redirection 285
Input redirection 285
Employing Pipes 287
Performing Math 289
The expr command 290
Using brackets 292
A floating-point solution 293
The basics of bc 293
Using bc in scripts 295
Exiting the Script 297
Checking the exit status 297
The exit command 298
Working through a Practical Example 300
Summary 301
Chapter 12: Using Structured Commands 303
Working with the if-then Statement 303
Exploring the if-then-else Statement 306
Nesting ifs 307
Trying the test Command 311
Using numeric comparisons 313
Using string comparisons 314
Looking at string equality 315
Looking at string order 316
Looking at string size 318
Using file comparisons 320
Checking directories 320
Checking whether an object exists 321
Checking for a file 322
Checking for read access 324
Checking for empty files 325
Checking whether you can write to a file 326
Checking whether you can run a file 327
Checking ownership 328
Checking default group membership 329
Checking file date 330
Considering Compound Testing 331
Working with Advanced if-then Features 332
Using single parentheses 332
Using double parentheses 333
Using double brackets 335
Considering the case Command 335
Working through a Practical Example 337
Summary 343
Chapter 13: More Structured Commands 345
Looking at the for Command 345
Reading values in a list 346
Reading complex values in a list 347
Reading a list from a variable 349
Reading values from a command 350
Changing the field separator 351
Reading a directory using wildcards 352
Trying the C-Style for Command 354
The C language for command 355
Using multiple variables 356
Exploring the while Command 357
Basic while format 357
Using multiple test commands 358
Using the until Command 359
Nesting Loops 361
Looping on File Data 364
Controlling the Loop 365
The break command 365
Breaking out of a single loop 365
Breaking out of an inner loop 366
Breaking out of an outer loop 367
The continue command 368
Processing the Output of a Loop 371
Working through a Few Practical Examples 372
Finding executable files 373
Creating multiple user accounts 374
Summary 375
Chapter 14: Handling User Input 377
Passing Parameters 377
Reading parameters 377
Reading the script name 380
Testing parameters 381
Using Special Parameter Variables 382
Counting parameters 382
Grabbing all the data 384
Being Shifty 386
Working with Options 388
Finding your options 388
Processing simple options 388
Separating options from parameters 389
Processing options with values 391
Using the getopt command 392
Looking at the command format 392
Using getopt in your scripts 393
Advancing to getopts 395
Standardizing Options 398
Getting User Input 399
Reading basics 399
Timing Out 401
Reading with no display 402
Reading from a file 403
Working through a Practical Example 404
Summary 408
Chapter 15: Presenting Data 411
Understanding Input and Output 411
Standard file descriptors 412
STDIN 412
STDOUT 413
STDERR 414
Redirecting errors 414
Redirecting errors only 414
Redirecting errors and data 415
Redirecting Output in Scripts 416
Temporary redirections 416
Permanent redirections 417
Redirecting Input in Scripts 418
Creating Your Own Redirection 419
Creating output file descriptors 419
Redirecting file descriptors 420
Creating input file descriptors 421
Creating a read/write file descriptor 422
Closing file descriptors 423
Listing Open File Descriptors 424
Suppressing Command Output 426
Using Temporary Files 427
Creating a local temporary file 427
Creating a temporary file in /tmp 428
Creating a temporary directory 429
Logging Messages 430
Working through a Practical Example 431
Summary 433
Chapter 16: Script Control 435
Handling Signals 435
Signaling the Bash shell 435
Generating signals 436
Interrupting a process 436
Pausing a process 437
Trapping signals 438
Trapping a script exit 440
Modifying or removing a trap 441
Running Scripts in Background Mode 443
Running in the background 443
Running multiple background jobs 445
Running Scripts without a Hang-up 447
Controlling the Job 448
Viewing jobs 448
Restarting stopped jobs 450
Being Nice 451
Using the nice command 452
Using the renice command 453
Running like Clockwork 454
Scheduling a job using the at command 454
Understanding the at command format 454
Retrieving job output 455
Listing pending jobs 457
Removing jobs 457
Scheduling regular scripts 458
Looking at the cron table 458
Building the cron table 459
Viewing cron directories 460
Looking at the anacron program 460
Starting scripts with a new shell 462
Working through a Practical Example 463
Summary 469
Part III: Advanced Shell Scripting 471
Chapter 17: Creating Functions 473
Exploring Basic Script Functions 473
Creating a function 474
Using functions 474
Returning a Value from a Function 477
The default exit status 477
Using the return command 478
Using function output 479
Using Variables in Functions 480
Passing parameters to a function 480
Handling variables in a function 482
Global variables 483
Local variables 484
Investigating Array Variables and Functions 485
Passing arrays to functions 485
Returning arrays from functions 487
Considering Function Recursion 488
Creating a Library 489
Using Functions on the Command Line 491
Creating functions on the command line 491
Defining functions in the bashrc file 492
Directly defining functions 492
Sourcing function files 493
Working Through a Practical Example 494
Downloading and installing 494
Building the library 495
The shtool library functions 496
Using the library 497
Summary 497
Chapter 18: Writing Scripts for Graphical Desktops 499
Creating Text Menus 499
Create the menu layout 499
Create the menu functions 501
Add the menu logic 502
Putting it all together 502
Using the select command 504
Doing Windows 505
The dialog package 506
The msgbox widget 507
The yesno widget 508
The inputbox widget 508
The textbox widget 510
The menu widget 511
The fselect widget 512
The dialog options 513
Using the dialog command in a script 515
Getting Graphic 516
The KDE environment 517
kdialog widgets 517
Using kdialog 519
The GNOME environment 521
zenity Widgets 521
Using zenity in scripts 523
Working Through a Practical Example 525
Summary 529
Chapter 19: Introducing sed and gawk 531
Manipulating Text 531
Getting to know the sed editor 532
Defining an editor command in the command line 533
Using multiple editor commands in the command line 534
Reading editor commands from a file 534
Getting to know the gawk program 535
Visiting the gawk command format 536
Reading the program script from the command line 536
Using data field variables 537
Using multiple commands in the program script 538
Reading the program from a file 539
Running scripts before processing data 539
Running scripts after processing data 540
Looking at the sed Editor Basic Commands 542
Introducing more substitution options 542
Substituting flags 542
Replacing characters 543
Using addresses 544
Addressing the numeric line 544
Using text pattern filters 545
Grouping commands 546
Deleting lines 547
Inserting and appending text 549
Changing lines 551
Transforming characters 552
Printing revisited 553
Printing lines 554
Printing line numbers 555
Listing lines 555
Using files with sed 556
Writing to a file 556
Reading data from a file 557
Working Through a Practical Example 559
Summary 564
Chapter 20: Regular Expressions 565
Exploring Regular Expressions 565
A definition 565
Types of regular expressions 567
Defining BRE Patterns 567
Plain text 567
Special characters 569
Anchor characters 570
Starting at the beginning 570
Looking for the ending 571
Combining anchors 572
The dot character 572
Character classes 573
Negating character classes 575
Using ranges 576
Special character classes 577
The asterisk 578
Trying Out Extended Regular Expressions 579
The question mark 579
The plus sign 580
Using braces 581
The pipe symbol 582
Grouping expressions 583
Working Through Some Practical Examples 584
Counting directory files 584
Validating a phone number 585
Parsing an email address 587
Summary 589
Chapter 21: Advanced sed 591
Looking at Multiline Commands 591
Navigating the next command 592
Using the single-line next command 592
Combining lines of text 593
Navigating the multiline delete command 595
Navigating the multiline print command 596
Holding Space 598
Negating a Command 599
Changing the Flow 602
Branching 603
Testing 605
Replacing via a Pattern 606
Using the ampersand 606
Replacing individual words 607
Placing sed Commands in Scripts 608
Using wrappers 608
Redirecting sed output 609
Creating sed Utilities 610
Spacing with double lines 610
Spacing files that may have blanks 611
Numbering lines in a file 612
Printing last lines 613
Deleting lines 614
Deleting consecutive blank lines 615
Deleting leading blank lines 616
Deleting trailing blank lines 616
Removing HTML tags 617
Working Through a Practical Example 619
Summary 624
Chapter 22: Advanced gawk k 627
Using Variables 627
Built-in variables 628
The field and record separator variables 628
Data variables 631
User-defined variables 634
Assigning variables in scripts 634
Assigning variables on the command line 635
Working with Arrays 636
Defining array variables 636
Iterating through array variables 637
Deleting array variables 638
Considering Patterns 638
Regular expressions 639
The matching operator 639
Mathematical expressions 640
Structured Commands 641
The if statement 641
The while statement 643
The do-while statement 644
The for statement 645
Printing with Formats 645
Using Built-in Functions 648
Mathematical functions 649
String functions 650
Time functions 652
Trying Out User-Defined Functions 653
Defining a function 653
Using your functions 654
Creating a function library 654
Working Through a Practical Example 655
Summary 657
Chapter 23: Working with Alternative Shells 659
Considering the Dash Shell 659
Looking at the Dash Shell Features 661
The Dash command-line parameters 661
The Dash environment variables 662
Default environment variables 662
Positional parameters 663
User-defined environment variables 663
The Dash built-in commands 664
Scripting in Dash 665
Creating Dash scripts 665
Things that won’t work 665
Using arithmetic 666
The test command 666
The function command 667
Exploring the zsh Shell 668
Viewing Parts of the zsh shell 668
Shell options 669
Built-in commands 670
Core built-in commands 670
Add-in modules 673
Viewing, adding, and removing modules 673
Scripting with zsh 674
Mathematical operations 674
Performing calculations 674
Mathematical functions 675
Structured commands 676
Functions 677
Working Through a Practical Example 677
Summary 678
Part IV: Creating and Managing Practical Scripts 679
Chapter 24: Writing Simple Script Utilities 681
Performing Backups 681
Backing up files daily 682
Obtaining the required functions 682
Creating a daily archive location 685
Creating a daily backup script 686
Running the daily archive script 688
Creating an hourly archive script 689
Running the hourly archive script 692
Managing Account Deletion 693
Obtaining the required functions 693
Getting the correct account name 693
Creating a function to get the correct account name 695
Verifying the entered account name 696
Determining whether the account exists 698
Removing any account processes 699
Finding account files 702
Removing the account 702
Creating the script 703
Running the script 708
Monitoring Your System 710
Obtaining the default shell audit functions 710
Obtaining the permission audit functions 714
Creating the script 716
Running the script 719
Summary 721
Chapter 25: Getting Organized 723
Understanding Version Control 723
Working directory 724
Staging area 725
Looking at the local repository 725
Exploring a remote repository 726
Branching 726
Cloning 726
Using Git for VCS 727
Setting Up Your Git Environment 727
Committing with Git 732
Summary 739
Appendix A: Quick Guide to Bash Commands 741
Appendix B: Quick Guide to sed and gawk 755
Index 767
