🧠 Device & Peripheral I/O

Shell scripts frequently interact with system devices such as printers, USB devices, serial ports, disks, audio interfaces, and network adapters. This module provides a practical overview of how POSIX shells integrate with system peripherals using standard Linux interfaces.

🎓 Who This Is For

DevOps/SRE engineers managing Linux servers or workstations
Developers writing automation for hardware‑related tasks
Sysadmins working with printers, USB devices, or serial ports
Anyone needing predictable, scriptable access to system peripherals

🧩 Role in the Ecosystem

Linux exposes hardware through:

/dev/* device nodes
sysfs (/sys/class/*)
udev events and rules
system services (CUPS, NetworkManager, PulseAudio/PipeWire)
command‑line utilities (lp, lsusb, ip, amixer, scanimage, mount)

Shell scripts act as glue between these interfaces and higher‑level automation.

🧩 Key Concepts

1. Device Nodes

Hardware is represented as files:

/dev/sda — block devices
/dev/ttyUSB0 — serial adapters
/dev/lp0 — parallel printers
/dev/input/* — keyboards, mice

2. sysfs

Provides structured metadata:

ls /sys/class/net
ls /sys/class/usb_device

3. udev

Dynamic device management:

1	`udevadm info /dev/sda`

4. Permissions

Most device nodes require group membership (lp, dialout, audio, video).

🔧 Techniques

Printers (CUPS)

List printers:

1	`lpstat -p`

Print a file:

lp -d printer_name file.pdf

Check queue:

lpq

Cancel job:

1	`cancel JOB_ID`

USB Devices

List USB devices:

lsusb

Monitor hotplug events:

1	`udevadm monitor --udev`

Get detailed info:

udevadm info --query=all --name=/dev/sdb

Serial Ports (TTY)

Configure serial port:

stty -F /dev/ttyUSB0 9600 cs8 -cstopb -parenb

Read data:

1	`cat /dev/ttyUSB0`

Write data:

echo "AT" > /dev/ttyUSB0

Interactive session:

screen /dev/ttyUSB0 9600

Disks & Storage

List block devices:

lsblk

Identify filesystem:

1	`blkid /dev/sdb1`

Mount:

1	`mount /dev/sdb1 /mnt`

Unmount:

1	`umount /mnt`

Audio Devices

List sinks/sources:

pactl list short sinks

Set volume:

pactl set-sink-volume @DEFAULT_SINK@ +5%

Record audio:

arecord -d 5 out.wav

Network Interfaces

List interfaces:

ip link

Bring interface up/down:

ip link set eth0 up
ip link set eth0 down

Check Wi‑Fi:

iw dev

Scanners (SANE)

List scanners:

1	`scanimage -L`

Scan to file:

scanimage --format=png > out.png

⚠️ Limitations & Pitfalls

Device access often requires elevated permissions
Hotplug timing issues can break scripts
USB device names (/dev/sdX, /dev/ttyUSB*) are not stable
CUPS may require authentication
Audio backends differ (PulseAudio vs PipeWire vs ALSA)
Serial communication requires correct baud/parity settings
sysfs paths vary across kernel versions

🧠 When to Use Shell for Device I/O

Simple automation tasks
Monitoring device state
Integrating with existing CLI tools
Lightweight scripts for servers or embedded systems
Quick diagnostics and troubleshooting

❌ When Not to Use Shell

High‑performance data acquisition
Complex binary protocols
Real‑time communication
Applications requiring robust error recovery
Multi‑threaded or asynchronous I/O

Use a real language (Python, Go, Rust) for these cases.

✅ Best Practices

Use stable identifiers (UUIDs, labels, udev rules)
Avoid hard‑coding /dev/sdX paths
Validate device presence before use
Use udevadm settle for hotplug timing
Log all device interactions
Handle permissions gracefully
Use traps for cleanup:

trap 'umount /mnt' EXIT

🧪 Testing Device I/O

lsblk
lsusb
udevadm monitor
echo test > /dev/ttyUSB0
scanimage -L
ip link

🧠 Summary

Shell scripts provide a powerful interface to Linux peripherals through /dev, sysfs, udev, and system utilities. They are ideal for lightweight automation, diagnostics, and integration — but not for high‑performance or real‑time workloads.