> ## Documentation Index
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> Use this file to discover all available pages before exploring further.
# Bash Elif Clause
The `elif` (else-if) clause is a conditional control structure in Bash used within an `if` construct to evaluate sequential, mutually exclusive conditions. It allows for the chaining of multiple test expressions at the same logical depth, preventing the need for deeply nested `if...else` statements.
## Syntax
The `elif` clause must follow an initial `if` statement and precede an optional `else` statement. It requires its own `then` keyword to define the block of code to execute.
```bash theme={"dark"}
if command_1; then
# Executed if command_1 returns exit status 0
elif command_2; then
# Executed if command_1 returns non-zero AND command_2 returns exit status 0
elif command_3; then
# Executed if preceding commands return non-zero AND command_3 returns exit status 0
else
# Executed if all preceding commands return a non-zero exit status
fi
```
*Note: `command_n` is typically a test construct like `[ ]` (POSIX test), `[[ ]]` (Bash extended test), or `(( ))` (arithmetic evaluation), but it can be any standard Unix command.*
## Execution Mechanics
1. **Sequential Evaluation:** Bash evaluates `elif` conditions strictly from top to bottom. An `elif` condition is only evaluated if the preceding `if` statement, and any preceding `elif` statements, return a non-zero exit status (logical false).
2. **Short-Circuiting:** The moment an `elif` command returns an exit status of `0` (logical true), Bash executes the corresponding `then` block. Once that block completes, control jumps to the end of the entire `if...fi` construct. Subsequent `elif` clauses are not evaluated.
3. **Exit Status:** The exit status (`$?`) of the entire `if...elif...fi` construct is determined by the exit status of the last command executed within the triggered `then` block. If no conditions evaluate to `0` and no `else` block is present, the construct completes with an exit status of `0`.
## Structural Rules
* **Dependency:** An `elif` cannot exist independently; it must be bound to a parent `if` statement.
* **Multiplicity:** You can chain an arbitrary number of `elif` clauses within a single `if...fi` construct.
* **Placement:** All `elif` clauses must be declared before the `else` fallback clause, if one is utilized.
* **Termination:** The `elif` block does not require its own closing tag; the entire chain is terminated by the single `fi` keyword belonging to the parent `if` statement.
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