> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Args
> This guide explains handling command-line arguments in Bash scripts using positional parameters, special variables, and quoting techniques.
When writing Bash scripts, handling command-line arguments efficiently is crucial. You can access each argument by its position (`$1`, `$2`, …), but when the number of parameters varies, special variables like `$@` and `$*` simplify your logic. This guide covers:
* Positional parameters
* Grouping arguments
* Iterating with `"$@"` vs `"$*"`
* The impact of quoting
* Customizing the internal field separator (IFS)
* Compatibility considerations
***
## 1. Positional Parameters: `$1`, `$2`, …
By default, Bash assigns each argument to a numbered variable:
```bash theme={null}
#!/usr/bin/env bash
firstarg=$1
secondarg=$2
echo "First argument: ${firstarg}"
echo "Second argument: ${secondarg}"
```
```bash theme={null}
$ ./simple-args.sh "arg1"
First argument: arg1
Second argument:
$ ./simple-args.sh "arg1" "arg2"
First argument: arg1
Second argument: arg2
```
When you need to accept an unpredictable number of parameters, indexing each one becomes cumbersome. That’s where `$@` and `$*` come in.
***
## 2. Grouping All Arguments: `$@` vs `$*`
Both `$@` and `$*` collect *all* positional arguments:
```bash theme={null}
#!/usr/bin/env bash
packaged_args1="$@"
packaged_args2="$*"
echo "Using \$@: ${packaged_args1}"
echo "Using \$*: ${packaged_args2}"
```
```bash theme={null}
$ ./simple-args2.sh arg1 arg2 arg3
Using $@: arg1 arg2 arg3
Using $*: arg1 arg2 arg3
```
Both variables contain the full list of parameters, but they differ when you iterate over them.
***
## 3. Iterating with a For Loop
Compare two scripts that loop over their arguments:
```bash theme={null}
#!/usr/bin/env bash
echo "Number of arguments: $#"
echo "All arguments: $@"
for arg in "$@"; do
echo "Argument: $arg"
done
```
```bash theme={null}
#!/usr/bin/env bash
echo "Number of arguments: $#"
echo "All arguments: $*"
for arg in "$*"; do
echo "Argument: $arg"
done
```
```bash theme={null}
$ ./atsign-example1.sh one two three
Number of arguments: 3
All arguments: one two three
Argument: one
Argument: two
Argument: three
$ ./star-example1.sh one two three
Number of arguments: 3
All arguments: one two three
Argument: one two three
```
In the soda‐can analogy:
* `$@` places each can in its own compartment.
* `$*` pours all the soda into one big bottle—individual cans are no longer separate.
***
## 4. The Importance of Double Quotes
Always quote `$@` and `$*`:
* `"$@"` expands each argument separately.
* `"$*"` joins all arguments into a single string, separated by the first character of `IFS` (default: space).
Unquoted, both behave identically:
```bash theme={null}
#!/usr/bin/env bash
print_section_header() {
local title="$1"
echo "==============================="
echo "= Section ${title} ="
echo "==============================="
}
print_section_header "1: \$@"
echo "--> Output of \$@: $@"
echo "Looping \$@ without quotes:"
for arg in $@; do
echo "$arg"
done
print_section_header "2: \$*"
echo "--> Output of \$*: $*"
echo "Looping \$* without quotes:"
for arg in $*; do
echo "$arg"
done
```
```bash theme={null}
$ ./special-shell-noquotes.sh one two three
===============================
= Section 1: $@ =
===============================
--> Output of $@: one two three
Looping $@ without quotes:
one
two
three
===============================
= Section 2: $* =
===============================
--> Output of $*: one two three
Looping $* without quotes:
one
two
three
```
***
## 5. Modifying the Internal Field Separator (IFS)
You can change `IFS` to alter how `"$*"` joins arguments:
```bash theme={null}
#!/usr/bin/env bash
IFS=','
echo "Output of \$@: $@"
echo "Output of \$*: $*"
```
```bash theme={null}
$ ./modified-ifs-v1.sh one two three
Output of $@: one two three
Output of $*: one,two,three
```
Splitting later requires unquoted iteration:
```bash theme={null}
#!/usr/bin/env bash
IFS='_'
args_at="$@"
args_star="$*"
print_section_header() { ... }
print_section_header "1: \$@"
echo "--> \$@: $@"
echo "Looping over args_at:"
for arg in $args_at; do
echo "$arg"
done
print_section_header "2: \$*"
echo "--> \$*: $*"
echo "Looping over args_star:"
for arg in $args_star; do
echo "$arg"
done
```
***
## 6. Compatibility with Older Bash Versions
Some pre-4.0 Bash releases split unquoted assignments differently. For example, under Bash 3:
```bash theme={null}
#!/usr/bin/env bash
IFS=','
args_at=$@
echo "--> \$@: ${args_at}"
for arg in $args_at; do
echo "$arg"
done
```
Still, quoting on assignment ensures consistent splitting:
```bash theme={null}
#!/usr/bin/env bash
IFS=','
args_at="$@"
echo "--> \$@: $@"
for arg in $args_at; do
echo "$arg"
done
```
***
## 7. Summary: `$@` vs `$*`
| Variable | Quoted Expansion | Unquoted Expansion | Use Case |
| -------- | -------------------- | ------------------ | ----------------------------------------------- |
| `$@` | Each arg is separate | Each word separate | Looping over arguments |
| `$*` | All args as one | Splits on `IFS` | Passing all args to another command or function |
***
## 8. Conclusion
* Use `"$@"` when you need to preserve each argument.
* Use `"$*"` to aggregate them into a single string with a custom delimiter.
* Always quote both to maintain consistent behavior across Bash versions and avoid word-splitting pitfalls.
***
## Links and References
* [Bash Reference Manual – Special Parameters](https://www.gnu.org/software/bash/manual/html_node/Special-Parameters.html)
* [Shell Parameter Expansion](https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html)
* [Advanced Bash-Scripting Guide](https://tldp.org/LDP/abs/html/)