Bash Reserved Words

Also called: Bash Keywords, Bash Language Keywords, Bash Reserved Words, Bash Reserved Keywords, Bash Reserved Identifiers

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Like any programming language, the Bash language designates certain words that the Bash interpreter (the specific Linux shell or Unix shell) recognizes as special words. For that reason, you're not allowed to use them for Bash naming | naming your Bash constructs. The list of Bash reserved words (also called Bash keywords) is surprisingly short:

Reserved words are words that have special meaning to the shell. They are used to begin and end the shell’s compound commands.

Creating a glossary of Bash reserved words sorted by their frequency of use is somewhat subjective, as it depends on what kinds of scripts are being written. Common scripting tasks often involve iteration, conditionals, and defining functions, which will guide our list of commonly used reserved words. Here's an attempt to outline these, formatted in MediaWiki markup:

```mediawiki

Bash Reserved Words Glossary

This glossary lists Bash reserved words that are frequently used in shell scripting. Each entry includes a brief code example to illustrate its usage.

if

The `if` statement is used to execute commands based on a condition.

if [ "$a" -eq "$b" ]; then
    echo "a equals b"
fi

else

The `else` statement is used to execute commands if the `if` condition is false.

if [ "$a" -eq "$b" ]; then
    echo "a equals b"
else
    echo "a does not equal b"
fi

elif

The `elif` (else if) statement allows for multiple conditions.

if [ "$a" -eq "$b" ]; then
    echo "a equals b"
elif [ "$a" -gt "$b" ]; then
    echo "a is greater than b"
else
    echo "a is less than b"
fi

for

The `for` loop is used to iterate over a series of values.

for i in 1 2 3; do
    echo "$i"
done

while

The `while` loop executes as long as a condition is true.

while [ "$a" -lt 10 ]; do
    echo "$a"
    a=$((a + 1))
done

do

The `do` keyword is used with loops (`for`, `while`, `until`) to start the execution block.

for i in 1 2 3; do
    echo "$i"
done

done

The `done` keyword is used to end a loop (`for`, `while`, `until`).

while [ "$a" -lt 10 ]; do
    echo "$a"
    a=$((a + 1))
done

function

The `function` keyword is used to define a function.

function my_func() {
    echo "Hello World"
}

case

The `case` statement allows branching based on patterns.

case "$1" in
    start)
        echo "Starting"
        ;;
    stop)
        echo "Stopping"
        ;;
    *)
        echo "Usage: $0 start]] | [[stop"
        ;;
esac

esac

The `esac` keyword is used to end a `case` statement.

case "$1" in
    start]] | [[stop) echo "Will start or stop" ;;
    *) echo "Unknown command" ;;
esac

in

The `in` keyword is used with `case` and `for` statements to specify a list.

for i in $(seq 1 3); do
    echo "$i"
done

until

The `until` loop is used to execute commands until a condition is true.

until [ "$a" -ge 10 ]; do
    echo "$a"
    a=$((a + 1))
done

select

The `select` statement is used to generate a menu from a list of items.

select choice in "Option 1" "Option 2" "Option 3"; do
    case $REPLY in
        1) echo "Selected Option 1"; break ;;
        2) echo "Selected Option 2"; break ;;
        3) echo "Selected Option 3"; break ;;
        *) echo "Invalid selection"; break ;;
    esac
done

This list includes some of the most commonly used Bash reserved words, ideal for beginners and those looking to understand shell scripting better. Bash scripting allows for complex flow control, function definitions, and system automation with these and other reserved words. ```

This format is designed for easy inclusion in a MediaWiki-based site, offering clear examples and explanations to help readers quickly understand the use of each reserved word in Bash scripting.

The following words are recognized as reserved when unquoted and the first word of a command (see below for exceptions):

{ } bash_reserved_words !

in is recognized as a reserved word if it is the third word of a case or select command. in and do are recognized as reserved words if they are the third word in a for command.

https://www.gnu.org/software/bash/manual/html_node/Reserved-Words.html