Bash

https://www.gnu.org/software/bash/manual/html_node/
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Bash (Bourne-Again SHell) is a Unix shell and command language interpreter that incorporates...
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### select example: pick a file

Source: https://www.gnu.org/software/bash/manual/html_node/Conditional-Constructs.html

Example using select to let the user pick a filename from the current directory and display the selection.

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

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

### Preview installation with DESTDIR

Source: https://www.gnu.org/software/bash/manual/html_node/Installation-Names.html

Use DESTDIR to see where files will be installed without changing the system. The value should be an absolute directory path used as the root of the sample installation tree.

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

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

### case example: animal features

Source: https://www.gnu.org/software/bash/manual/html_node/Conditional-Constructs.html

Example script using case to describe an animal feature based on user input.

```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: ${parameter:?word} and ${parameter?word} examples

Source: https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html

Shows how the :? operator writes an error message to standard error and exits with a non-zero status (if not interactive) when the parameter is null or unset. The examples demonstrate the difference between including and omitting the colon, and the behavior when the parameter is set.

```bash
$ var=
$ : ${var:?var is unset or null}
bash: var: var is unset or null
$ echo ${var?var is unset}

$ unset var
$ : ${var?var is unset}
bash: var: var is unset
$ : ${var:?var is unset or null}
bash: var: var is unset or null
$ var=123
$ echo ${var:?var is unset or null}
123

```

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

### Set configure variables using env

Source: https://www.gnu.org/software/bash/manual/html_node/Compilers-and-Options.html

On systems with the env program, use env to set configure variables. This example sets CPPFLAGS=-I/usr/local/include and LDFLAGS=-s.

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

```

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

### Install _comp_cd with complete -F for cd

Source: https://www.gnu.org/software/bash/manual/html_node/A-Programmable-Completion-Example.html

Installs the _comp_cd function for the cd command using the -F option. The -o filenames option tells Readline to treat completions as filenames and quote appropriately, -o nospace prevents appending a space, and -o bashdefault brings in Bash default completions.

```bash
# Tell readline to quote appropriate and append slashes to directories;
# use the bash default completion for other arguments
complete -o filenames -o nospace -o bashdefault -F _comp_cd cd

```

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

### Compile PO to MO with msgfmt

Source: https://www.gnu.org/software/bash/manual/html_node/Creating-Internationalized-Scripts.html

Compiles a .po file into a .mo message catalog using msgfmt. Example produces es.mo from es.po.

```bash
msgfmt -o es.mo es.po

```

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

### Anchored pattern with quoted literal

Source: https://www.gnu.org/software/bash/manual/html_node/Conditional-Constructs.html

Example of anchoring a pattern at the start of a string while quoting a literal portion. This works because the '^' is not quoted.

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

```

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

### Bash asynchronous job output: [1] 25647

Source: https://www.gnu.org/software/bash/manual/html_node/Job-Control-Basics.html

When Bash starts a job asynchronously, it prints a line showing the job number in brackets and the process ID of the last process in the pipeline. This example shows job number 1 with process ID 25647.

```bash
[1] 25647

```

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

### View configure options with ./configure --help

Source: https://www.gnu.org/software/bash/manual/html_node/Basic-Installation.html

Run this command in the Bash source directory to see the options and arguments that the configure script understands.

```bash
bash-4.2$ ./configure --help

```

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

### Set TEXTDOMAIN and TEXTDOMAINDIR and install MO files

Source: https://www.gnu.org/software/bash/manual/html_node/Creating-Internationalized-Scripts.html

Sets the message domain and directory, then copies MO files to language-specific LC_MESSAGES directories. Uses the convention $TEXTDOMAINDIR/$LC_MESSAGES/LC_MESSAGES/$TEXTDOMAIN.mo.

```bash
TEXTDOMAIN=example
TEXTDOMAINDIR=/usr/local/share/locale

cp es.mo ${TEXTDOMAINDIR}/es/LC_MESSAGES/${TEXTDOMAIN}.mo
cp eo.mo ${TEXTDOMAINDIR}/eo/LC_MESSAGES/${TEXTDOMAIN}.mo

```

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

### Create a build directory with symbolic links using support/mkclone

Source: https://www.gnu.org/software/bash/manual/html_node/Compiling-For-Multiple-Architectures.html

Use this command to create a build directory in the current directory from a source directory, with symbolic links back to each source file. The mkclone script requires Bash, so you must have already built Bash for at least one architecture before using it.

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

```

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

### help command syntax

Source: https://www.gnu.org/software/bash/manual/html_node/Bash-Builtins.html

Syntax for the help builtin. Options include -d for short descriptions, -m for man-page format, and -s for usage only.

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

```

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

### Bash: ${parameter:=word} and ${parameter=word} examples

Source: https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html

Shows how the := operator assigns the default value to the parameter when it is unset or null, while the = operator only assigns when the parameter is unset. The examples use : ${var=DEFAULT} and : ${var:=DEFAULT} to demonstrate the difference.

```bash
$ unset var
$ : ${var=DEFAULT}
$ echo $var
DEFAULT
$ var=
$ : ${var=DEFAULT}
$ echo $var

$ var=
$ : ${var:=DEFAULT}
$ echo $var
DEFAULT
$ unset var
$ : ${var:=DEFAULT}
$ echo $var
DEFAULT

```

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

### Bash: ${parameter:+word} and ${parameter+word} examples

Source: https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html

Shows how the :+ operator substitutes the word only when the parameter is set and not null, while the + operator substitutes the word when the parameter is set (even if null). The examples demonstrate the difference with a set, null, and unset variable.

```bash
$ var=123
$ echo ${var:+var is set and not null}
var is set and not null
$ echo ${var+var is set}
var is set
$ var=
$ echo ${var:+var is set and not null}

$ echo ${var+var is set}
var is set
$ unset var
$ echo ${var+var is set}

$ echo ${var:+var is set and not null}

$ 

```

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

### Create gettext template with bash --dump-po-strings

Source: https://www.gnu.org/software/bash/manual/html_node/Creating-Internationalized-Scripts.html

Generates a .pot template file from a script with marked strings. Redirect output to a file with .pot suffix.

```bash
bash --dump-po-strings scriptname > domain.pot

```
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