> ## Documentation Index
> Fetch the complete documentation index at: https://docs.syntblaze.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Bash Modulo
The `%` operator in Bash serves three distinct syntactic roles depending on its evaluation context: an arithmetic modulo operator, a parameter expansion operator for suffix removal, and a job control specifier.
## Arithmetic Modulo Operator
Within an arithmetic evaluation context, `%` functions as the modulo operator. It evaluates the remainder of integer division between two operands. Because Bash natively supports only integer arithmetic, floating-point operands will result in a syntax error.
**Syntax:**
```bash theme={"dark"}
$(( dividend % divisor ))
(( dividend % divisor ))
let "var = dividend % divisor"
```
**Mechanics:**
* Evaluated exclusively inside Bash's internal arithmetic contexts (`$(( ))`, `(( ))`, or `let`).
* The sign of the result matches the sign of the dividend.
* Division by zero throws a `division by 0` runtime error.
**Example:**
```bash theme={"dark"}
echo $(( 10 % 3 )) # Outputs: 1
echo $(( -10 % 3 )) # Outputs: -1
```
## Parameter Expansion (Suffix Pattern Removal)
Within parameter expansion, `%` acts as a pattern-matching operator that strips a specified suffix from a variable's string value. It uses standard shell globbing rules (not regular expressions) to match the pattern against the end of the string.
**Syntax:**
```bash theme={"dark"}
${variable%pattern} # Non-greedy (shortest match)
${variable%%pattern} # Greedy (longest match)
```
**Mechanics:**
* **Single `%` (Non-greedy):** Deletes the shortest possible match of the `pattern` from the right side (suffix) of the expanded `$variable`.
* **Double `%%` (Greedy):** Deletes the longest possible match of the `pattern` from the right side of the expanded `$variable`.
* If the pattern does not match the suffix, the original string is returned unmodified.
**Example:**
```bash theme={"dark"}
string="base.module.ext"
echo ${string%.*} # Outputs: base.module (strips shortest match of ".*")
echo ${string%%.*} # Outputs: base (strips longest match of ".*")
```
## Job Control Specifier
In an interactive shell environment (or scripts where `set -m` is enabled), `%` is used as a prefix to reference background or suspended jobs by their job ID or command string, rather than their Process ID (PID).
**Syntax:**
```bash theme={"dark"}
% # References the current job (synonym for %% and %+)
%% # References the current (most recently foregrounded/backgrounded) job
%+ # Same as %%
%- # References the previous job
%n # References job number 'n'
%string # References the job whose command begins with 'string'
%?string # References the job whose command contains 'string'
```
**Example:**
```bash theme={"dark"}
fg %1 # Brings job 1 to the foreground
kill -15 % # Sends SIGTERM to the current job
```
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