### Simulate Installation with DESTDIR

Source: https://devdocs.io/bash/installation-names

Use the `DESTDIR` variable with `make install` to preview where files will be installed without actually modifying the system. The value of `DESTDIR` acts as a root for the simulated installation tree.

```bash
mkdir /fs1/bash-install
make install DESTDIR=/fs1/bash-install
```

--------------------------------

### Tilde Expansion Examples

Source: https://devdocs.io/bash/tilde-expansion

Illustrates various forms of tilde expansion and their corresponding replacements.

```bash
~
```

```bash
~/foo
```

```bash
~fred/foo
```

```bash
~+/foo
```

```bash
~-/foo
```

```bash
~N
```

```bash
~+N
```

```bash
~-N
```

--------------------------------

### Bash: Example of set -P behavior

Source: https://devdocs.io/bash/the-set-builtin

This example demonstrates the difference in directory traversal when `set -P` is enabled versus the default behavior. Without `set -P`, `cd ..` moves up the logical directory structure. With `set -P`, it moves up the physical directory structure.

```bash
$ cd /usr/sys; echo $PWD
/usr/sys
$ cd ..; pwd
/

If `set -P` is on, then:

$ cd /usr/sys; echo $PWD
/usr/local/sys
$ cd ..; pwd
/usr/local
```

--------------------------------

### Specify Separate Prefixes for Executable and Data Files

Source: https://devdocs.io/bash/installation-names

Use `exec_prefix` to set a specific installation path for programs and libraries, while `prefix` continues to be used for documentation and data files. This allows for architecture-specific and architecture-independent files to be installed in different locations.

```bash
make install exec_prefix=/path/to/executables
```

--------------------------------

### Directory Creation with Brace Expansion

Source: https://devdocs.io/bash/brace-expansion

Provides an example of using brace expansion to create multiple directories with common prefixes and suffixes.

```bash
mkdir /usr/local/src/bash/{old,new,dist,bugs}
```

--------------------------------

### Change Installation Locations for a Single Run

Source: https://devdocs.io/bash/installation-names

Modify installation directories for a single `make install` command by specifying `exec_prefix` and `prefix` as arguments. This is useful for testing or temporary installations.

```bash
make install exec_prefix=/
```

--------------------------------

### Bash select Statement Example

Source: https://devdocs.io/bash/conditional-constructs

An example of the select statement that allows the user to pick a filename from the current directory and displays the chosen file and its index.

```bash
select fname in *;
do
	echo you picked $fname \($REPLY\)
	break;
done

```

--------------------------------

### Specify Installation Prefix with make

Source: https://devdocs.io/bash/installation-names

Use the `prefix` make variable to specify a custom installation path for Bash and related files. This variable also provides defaults for `exec_prefix` and other installation variables.

```bash
make install prefix=/path/to/custom/install
```

--------------------------------

### Create Build Directory with Symbolic Links

Source: https://devdocs.io/bash/compiling-for-multiple-architectures

Use the 'mkclone' script to create a build directory with symbolic links to the source directory. This method requires Bash to be installed for at least one architecture first.

```bash
bash /usr/gnu/src/bash-2.0/support/mkclone -s /usr/gnu/src/bash-2.0 .
```

--------------------------------

### Installing a Bash Completion Function

Source: https://devdocs.io/bash/a-programmable-completion-example

This command registers the previously defined completion function with the `complete` builtin, enabling programmable completions for the specified command.

```bash
# Tell readline to quote appropriate and append slashes to directories;

```

--------------------------------

### Bash case Statement Example

Source: https://devdocs.io/bash/conditional-constructs

An example demonstrating the use of the case statement to handle different animal inputs and describe their number of legs. Uses a default '*' pattern.

```bash
echo -n "Enter the name of an animal: "
read ANIMAL
echo -n "The $ANIMAL has "
case $ANIMAL in
  horse | dog | cat) echo -n "four";;
  man | kangaroo ) echo -n "two";;
  *) echo -n "an unknown number of";;
esac
echo " legs."

```

--------------------------------

### Bash Job Notification Example

Source: https://devdocs.io/bash/job-control-basics

This is an example of the output Bash displays when a job is started asynchronously. It indicates the job number and the process ID of the last process in the pipeline.

```bash
[1] 25647

```

--------------------------------

### Get Help on Bash Builtins

Source: https://devdocs.io/bash/bash-builtins

Provides help information for builtin commands. Use -d for short descriptions, -m for manpage-like format, or -s for a usage synopsis.

```bash
help [-dms] [pattern]
```

--------------------------------

### Bash OR List Example

Source: https://devdocs.io/bash/lists

Execute command2 only if command1 fails. The return status is that of the last command executed.

```bash
command1 || command2

```

--------------------------------

### Bash AND List Example

Source: https://devdocs.io/bash/lists

Execute command2 only if command1 succeeds. The return status is that of the last command executed.

```bash
command1 && command2

```

--------------------------------

### Get Length of Array Element or Count in Bash

Source: https://devdocs.io/bash/arrays

Get the length of a specific array element using `${#name[subscript]}`. Use `${#name[@]}` or `${#name[*]}` to get the number of elements in the array.

```bash
${#name[subscript]}
```

```bash
${#name[@]}
```

--------------------------------

### Bash --help Option

Source: https://devdocs.io/bash/invoking-bash

Displays a usage message on standard output and exits successfully.

```bash
--help
```

--------------------------------

### Bash Regex Match at Start of String

Source: https://devdocs.io/bash/conditional-constructs

Anchor a regular expression pattern to the start of a string using `^` within `[[ ... ]]`. Ensure the anchor is not quoted to maintain its special meaning.

```bash
[[ $line =~ ^"initial string" ]]
```

--------------------------------

### List All Shopt Options

Source: https://devdocs.io/bash/the-shopt-builtin

Lists all available shell options and their current settings. The `-p` flag formats the output for potential reuse as input.

```bash
shopt -p
```

--------------------------------

### Recommended Coprocess Form

Source: https://devdocs.io/bash/coprocesses

Presents the recommended syntax for using coprocesses, which is simpler and more complete for compound commands.

```bash
coproc NAME { command; }

```

--------------------------------

### Bash --init-file and --rcfile Options

Source: https://devdocs.io/bash/invoking-bash

Specifies an alternative initialization file to execute commands from instead of ~/.bashrc in an interactive shell.

```bash
--init-file filename

--rcfile filename
```

--------------------------------

### Bash --version Option

Source: https://devdocs.io/bash/invoking-bash

Displays version information for the current Bash instance on standard output and exits successfully.

```bash
--version
```

--------------------------------

### List Enabled Shopt Options

Source: https://devdocs.io/bash/the-shopt-builtin

Shows only the shell options that are currently enabled. This is useful for understanding the active configurations.

```bash
shopt -s
```

--------------------------------

### Bash --debugger Option

Source: https://devdocs.io/bash/invoking-bash

Enables extended debugging mode by executing the debugger profile before the shell starts.

```bash
--debugger
```

--------------------------------

### Bash: Select Command by Prefix and Argument

Source: https://devdocs.io/bash/word-designators

Use `!fi:2` to select the second argument of the most recent command that started with `fi`.

```bash
!fi:2
    
designates the second argument of the most recent command starting with the letters `fi`.
```

--------------------------------

### Set Compiler Options via Environment Variables

Source: https://devdocs.io/bash/compilers-and-options

Use this method to pass specific compiler and linker flags to the `configure` script when it doesn't automatically detect them. Requires a Bourne-compatible shell.

```bash
CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure

```

--------------------------------

### Conditional Initialization Based on Readline Version

Source: https://devdocs.io/bash/conditional-init-constructs

Sets 'show-mode-in-prompt' if the Readline version is 7.0 or newer. Use for version-specific configurations.

```bash
$if version >= 7.0
set show-mode-in-prompt on
$endif

```

--------------------------------

### Bash Shell Level with SHLVL

Source: https://devdocs.io/bash/bash-variables

SHLVL is incremented each time a new Bash instance is started, indicating the depth of nested shells.

```bash
SHLVL
```

--------------------------------

### Include Bashrc in Bash Profile

Source: https://devdocs.io/bash/bash-startup-files

This snippet is typically placed in ~/.bash_profile to ensure that ~/.bashrc is sourced when an interactive non-login shell is started.

```bash
if [ -f ~/.bashrc ]; then . ~/.bashrc; fi
```

--------------------------------

### Include External Configuration File

Source: https://devdocs.io/bash/conditional-init-constructs

Reads configuration settings from another file, typically '/etc/inputrc'. Use this to modularize your inputrc configuration.

```bash
$include /etc/inputrc

```

--------------------------------

### Get Array Indices in Bash

Source: https://devdocs.io/bash/arrays

Expand to the assigned indices of an array variable. The behavior within double quotes is similar to `${name[@]}` and `${name[*]}`.

```bash
${!name[@]}
```

```bash
${!name[*]}
```

--------------------------------

### Shopt Builtin Syntax

Source: https://devdocs.io/bash/the-shopt-builtin

Displays the syntax for the `shopt` builtin command. Use options like `-s` to enable, `-u` to disable, and `-p` to list options.

```bash
shopt [-pqsu] [-o] [optname …]
```

--------------------------------

### Get Parameter Length

Source: https://devdocs.io/bash/shell-parameter-expansion

Substitutes the length in characters of the expanded value of parameter. For '*' or '@', it's the number of positional parameters. For arrays, it's the number of elements.

```bash
${#parameter}
```

--------------------------------

### Bash Process Substitution Syntax

Source: https://devdocs.io/bash/process-substitution

Illustrates the basic syntax for process substitution using `<(list)` for input and `>(list)` for output.

```bash
<(list)
```

```bash
>(list)
```

--------------------------------

### Shell Uptime with SECONDS

Source: https://devdocs.io/bash/bash-variables

SECONDS expands to the number of seconds since the shell started. Assignment resets the counter. It loses special properties if unset.

```bash
SECONDS
```

--------------------------------

### Bash: Select First Word from Search

Source: https://devdocs.io/bash/word-designators

The word designator `%` selects the first word matched by a `?string?` search, provided the search string starts a word.

```bash
%
    
The first word matched by the most recent ‘?string?’ search, if the search string begins with a character that is part of a word.
```

--------------------------------

### Executing a Shell Script

Source: https://devdocs.io/bash/shell-scripts

Demonstrates the syntax for executing a shell script with arguments. This is equivalent to invoking bash directly with the script.

```shell
filename arguments

```

```shell
bash filename arguments

```

--------------------------------

### Display Directory Stack with Full Pathnames

Source: https://devdocs.io/bash/directory-stack-builtins

Use the `-l` option with `dirs` to display full pathnames instead of using tilde expansion for the home directory.

```bash
dirs -l
```

--------------------------------

### Substring Expansion

Source: https://devdocs.io/bash/shell-parameter-expansion

Extract a substring from 'parameter' starting at 'offset' and extending up to 'length' characters. Negative offsets count from the end of the string. Omitting 'length' extracts to the end.

```bash
$ string=01234567890abcdefgh
$ echo ${string:7}
7890abcdefgh
```

```bash
$ echo ${string:7:0}

```

```bash
$ echo ${string:7:2}
78
```

```bash
$ echo ${string:7:-2}
7890abcdef
```

```bash
$ echo ${string: -7}
bcdefgh
```

```bash
$ echo ${string: -7:0}

```

```bash
$ echo ${string: -7:2}
bc
```

```bash
$ echo ${string: -7:-2}
bcdef
```

--------------------------------

### Bash: Unset Positional Parameters with set --

Source: https://devdocs.io/bash/the-set-builtin

Use `set --` to unset all positional parameters. If arguments follow, they are assigned to positional parameters, even if they start with a hyphen.

```bash
set --
```

--------------------------------

### Alternative Coprocess Forms

Source: https://devdocs.io/bash/coprocesses

Illustrates other valid forms for defining coprocesses, including variations for compound and simple commands.

```bash
coproc NAME compound-command
coproc compound-command
coproc simple-command

```

--------------------------------

### Set Compiler Options using `env`

Source: https://devdocs.io/bash/compilers-and-options

An alternative method to set environment variables for `configure`, useful on systems with the `env` program. This allows specifying include paths and linker flags.

```bash
env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure

```

--------------------------------

### Read Lines into Array with mapfile

Source: https://devdocs.io/bash/bash-builtins

Use `mapfile` to read lines from standard input or a file descriptor into an indexed array. Options control delimiters, line limits, starting index, and trailing character removal.

```bash
mapfile -d "," -n 10 -O 5 -s 2 -t -u 3 array
```

--------------------------------

### Bash Regex Match with Optional Character

Source: https://devdocs.io/bash/conditional-constructs

Use the `=~` operator within `[[ ... ]]` for POSIX extended regular expression matching. This example checks if a string contains zero or more whitespace characters followed by an optional 'a' and then a 'b'.

```bash
[[ $line =~ [[:space:]]*(a)?b ]]
```

--------------------------------

### Bash --verbose Option

Source: https://devdocs.io/bash/invoking-bash

Prints shell input lines as they are read, equivalent to -v.

```bash
--verbose
```

--------------------------------

### Substring Expansion on Positional Parameters

Source: https://devdocs.io/bash/shell-parameter-expansion

Extract a substring from a positional parameter ('$1', '$2', etc.) starting at 'offset' and extending up to 'length' characters. Negative offsets count from the end of the string. Omitting 'length' extracts to the end.

```bash
$ set -- 01234567890abcdefgh
$ echo ${1:7}
7890abcdefgh
```

```bash
$ echo ${1:7:0}

```

```bash
$ echo ${1:7:2}
78
```

```bash
$ echo ${1:7:-2}
7890abcdef
```

```bash
$ echo ${1: -7}
bcdefgh
```

```bash
$ echo ${1: -7:0}

```

```bash
$ echo ${1: -7:2}
bc
```

```bash
$ echo ${1: -7:-2}
bcdef
```

--------------------------------

### Basic Brace Expansion

Source: https://devdocs.io/bash/brace-expansion

Demonstrates generating strings with a common prefix and suffix from a comma-separated list within braces.

```bash
echo a{d,c,b}e
```

--------------------------------

### Assign Multiple Values to Indexed Array in Bash

Source: https://devdocs.io/bash/arrays

Assign multiple values to an indexed array using compound assignment. If no subscript is provided, elements are assigned to consecutive indices starting from the last assigned index plus one.

```bash
name=(value1 value2 … )
```

--------------------------------

### List Specific Shopt Options

Source: https://devdocs.io/bash/the-shopt-builtin

Lists the status of specified shell options. This helps in quickly checking the configuration of particular behaviors.

```bash
shopt -p assoc_expand_once cdspell
```

--------------------------------

### Configure `cd` command completion in Bash

Source: https://devdocs.io/bash/a-programmable-completion-example

Use the `complete` command with options to enable filename completion, prevent automatic spacing, and include Bash defaults for the `cd` command. This setup calls the `_comp_cd` function for word completion.

```bash
complete -o filenames -o nospace -o bashdefault -F _comp_cd cd
```

--------------------------------

### Display Directory Stack with One Entry Per Line

Source: https://devdocs.io/bash/directory-stack-builtins

The `-p` option for `dirs` prints each directory on a new line.

```bash
dirs -p
```