Table of Contents
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 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
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