Shell on Kyle's Blog

Toggle Color Theme on Plasma

Sun, 12 Oct 2025 12:07:36 +1100

Plasma introduced a quick settings panel in plasma 6, where you can toggle between Breeze and Breeze Dark themes. However, it will change the entire theme, ruining customizations like icons. You can toggle the color scheme manually by using the following command:

For dark theme:

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plasma-apply-desktoptheme breeze-dark && plasma-apply-colorscheme BreezeDark && plasma-apply-cursortheme Breeze_Light && /usr/lib/plasma-changeicons Papirus-Dark && /usr/bin/sed -i 's/DefaultProfile=Light.profile/DefaultProfile=Dark.profile/' ~/.config/konsolerc

For light theme:

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plasma-apply-desktoptheme breeze && plasma-apply-colorscheme Breeze && plasma-apply-cursortheme Breeze_Dark && /usr/lib/plasma-changeicons Papirus-Light && /usr/bin/sed -i 's/DefaultProfile=Dark.profile/DefaultProfile=Light.profile/' ~/.config/konsolerc

Before running the commands, ensure you have the Papirus icon theme installed and Light and Dark konsole profiles created. It will change the desktop theme, color scheme, cursor theme, icon theme, and konsole profile. Moreover, you can create two scripts and bind them to keyboard shortcuts for easy toggling.

24/10/25 Update

Plasma 6.5 was released, introducing a new feature to automatically switch between light and dark themes based on the time of day. However, it does not support custom icon themes and konsole profiles. A workaround is to run a script that monitors the theme change event and applies the necessary changes.

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#!/bin/bash

# Monitor KDE theme changes and execute commands

# Function to check current color scheme
check_theme() {
 # Query KDE's color scheme setting (KF6 uses kreadconfig6)
 theme=$(kreadconfig6 --file kdeglobals --group General --key ColorScheme)

 # Check if it's a dark theme (common dark themes contain "Dark" in name)
 if [[ $theme == *"Dark"* ]] || [[ $theme == *"Breeze Dark"* ]]; then
 echo "dark"
 else
 echo "light"
 fi
}

# Get initial state
previous_theme=$(check_theme)
echo "Current theme: $previous_theme"

# Monitor D-Bus for KDE settings changes
dbus-monitor --session "type='signal',interface='org.kde.KGlobalSettings',member='notifyChange'" | \
while read -r line; do
 # When we detect a change notification
 if [[ $line == *"notifyChange"* ]]; then
 sleep 0.5 # Small delay to ensure settings are written

 current_theme=$(check_theme)

 # Only act if theme actually changed
 if [[ $current_theme != $previous_theme ]]; then
 echo "Theme changed: $previous_theme -> $current_theme"

 if [[ $current_theme == "dark" ]]; then
 echo "Executing dark theme commands..."
 # Add your dark theme commands here
 notify-send "Dark Mode" "Switched to dark theme"
 /usr/lib/plasma-changeicons Papirus-Dark && /usr/bin/sed -i 's/DefaultProfile=Light.profile/DefaultProfile=Dark.profile/' ~/.config/konsolerc

 elif [[ $current_theme == "light" ]]; then
 echo "Executing light theme commands..."
 # Add your light theme commands here
 notify-send "Light Mode" "Switched to light theme"
 /usr/lib/plasma-changeicons Papirus-Light && /usr/bin/sed -i 's/DefaultProfile=Dark.profile/DefaultProfile=Light.profile/' ~/.config/konsolerc
 fi

 previous_theme=$current_theme
 fi
 fi
done

A user-level systemd service can be created to run this script in the background:

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[Unit]
Description=KDE Theme Monitor
After=graphical-session.target

[Service]
Type=simple
ExecStart=/home/username/.local/bin/theme-monitor.sh
Restart=on-failure

[Install]
WantedBy=default.target

And the commands to enable and start the service:

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systemctl --user enable theme-monitor.service
systemctl --user start theme-monitor.service

Even though this solution works, it’s quite hacky and heavy. Hoping for a better built-in feature in the future Plasma releases.

One Time Reboot to Win Shortcut

Tue, 16 Sep 2025 23:00:17 +1000

Reboot to Windows Once from Linux

On a dual-boot machine, you may occasionally want to reboot into Windows from Linux for a specific task—such as using a Windows-only application—and then return to Linux afterward. While GRUB allows you to choose which OS to boot, it is more convenient to have a one-time reboot option that boots directly into Windows, then automatically returns to Linux as the default on subsequent boots. This can be accomplished using efibootmgr to set the next boot entry to Windows.

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sudo efibootmgr -n <WindowsBootEntryNumber>

Here, <WindowsBootEntryNumber> is the boot entry number for Windows, which you can find by running efibootmgr without any arguments. The output will list all boot entries and their numbers. For example:

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BootCurrent: 0005
Timeout: 2 seconds
BootOrder: 0005,0004,2001,2002,2003
Boot0001* EFI PXE 0 for IPv4
Boot0002* EFI PXE 0 for IPv6
Boot0004* Windows Boot Manager
Boot0005* GRUB

To set the next boot to Windows, run:

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efibootmgr -n 0004

After executing this command, reboot your machine. It will boot into Windows for that session. On the next reboot, it will default back to Linux.

Creating a Shortcut Script

To streamline this process, create a simple script at /usr/local/bin/reboot2win:

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#!/usr/bin/env bash
# reboot2win: A script to reboot into Windows once
logger -t reboot2win "reboot2win executed by ${SUDO_USER:-$USER}"
# privileged command(s) below:
/usr/bin/efibootmgr -n 0004 && /usr/bin/systemctl reboot

Make it executable and set ownership to root for security:

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sudo chmod +x /usr/local/bin/reboot2win && sudo chown root:root /usr/local/bin/reboot2win

Now you can run sudo reboot2win to reboot into Windows once.

Make It Even Easier with Polkit

To avoid typing sudo every time, you can create a polkit rule to allow your user to run the script without a password prompt. Create a file at /etc/polkit-1/rules.d/50-reboot2win.rules with the following content:

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polkit.addRule(function (action, subject) {
 if (action.id == "org.freedesktop.policykit.exec") {
 var program = action.lookup("program");
 if (
 program == "/usr/local/bin/reboot2win" &&
 subject.isInGroup("wheel") &&
 subject.local &&
 subject.active
 ) {
 return polkit.Result.YES;
 }
 }
 return polkit.Result.NOT_HANDLED;
});

This rule allows users in the wheel group to execute the reboot2win script without a password prompt. Adjust the group name if your user belongs to a different group.

To apply the rule, restart the polkit service:

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sudo systemctl restart polkit

Now you can simply run the following command without sudo:

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pkexec /usr/local/bin/reboot2win

Finally, you can add an alias or a desktop shortcut for easier access. Also, to avoid accidentally running the command, you can use a confirmation prompt dialog such as kdialog or zenity. For example, using kdialog:

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bash -lc 'kdialog --yesno "Are you sure you want to reboot the system?"' && pkexec /usr/local/bin/reboot2win

This will show a confirmation dialog before executing the reboot command.

GNU Parallel 的妙用

Thu, 08 Jun 2023 00:00:00 +0000

Android QQ 的图片文件是以下面这种结构保存的，以Cache_开头的文件就是图片。这种结构在浏览时要分别点进每个文件夹才能看到图片，很不方便。

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├── 0a0
│   ├── Cache_2783644ca99260a0
│   └── Cache_-4dfb57e9a7cec0a0
├── 0a6
│   ├── Cache_373e35b7b8a290a6
│   ├── Cache_-489f6e9c62ea10a6
│   └── Cache_57776dc1e17110a6
└── 0a7
 └── Cache_25d732f84bd7d0a7

使用 GNU Parallel 配合mv可以快速的 “解散” 每个二级文件夹，变成以下这种结构。

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.
├── Cache_25d732f84bd7d0a7
├── Cache_2783644ca99260a0
├── Cache_373e35b7b8a290a6
├── Cache_-489f6e9c62ea10a6
├── Cache_-4dfb57e9a7cec0a0
└── Cache_57776dc1e17110a6

命令如下:

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find . -name "*" -type f -print | parallel mv {} ./{/}

参考: https://www.myfreax.com/gnu-parallel/

使用 Shell 批量修改文件后缀和批量格式转换

Tue, 06 Jun 2023 00:00:00 +0000

shell 脚本是处理这类工作最为简单，快捷的方式。

修改后缀

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for file in *.原后缀; do mv "$file" "`echo $file | sed s/.原后缀/.新后缀/`"; done

格式转换

heic 转 jpg

首先，安装转换工具。

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yay -S libheif

然后可以使用 heif-convert 命令转换。

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heif-convert input.heic output.jpg

批量转换，命令如下。

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for file in *.heic; do heif-convert "$file" ${file/%.heic/.jpg} && rm "$file"; done

这条命令的原理是：根据当前文件夹下的 .heic 文件生成 .jpg 文件，如果成功生成则删除原 .heic 文件，如果未成功则不会删除原文件。此外，如果未能生成 .jpg 文件的原因是 Input file 'filename.heic' is a JPEG image ，那么可以使用批量修改后缀的方法直接将文件的后缀改为 .jpg。

flac 转 mp3

首先，安装转换工具：

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yay -S ffmpeg

然后可以使用 ffmpeg 命令转换，除了格式转换，ffmpeg 还支持很多功能，具体可以查阅文档。

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ffmpeg -i 'input.flac' -ab 320k -map_metadata 0 -id3v2_version 3 'output.mp3'

批量转换，命令如下：

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for file in *.flac; do ffmpeg -i "$file" -ab 320k -map_metadata 0 -id3v2_version 3 ${file/%.flac/.mp3} && rm "$file"; done

原理同上。

速度优化

使用 for 循环的方式，所有文件排着队一个一个的被 ffmpeg 处理。这种方式固然可以，但效率太低了。我的运行环境如下:

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 -` momo@momo-arch
 .o+` --------------
 `ooo/ OS: Arch Linux x86_64
 `+oooo: Host: 81AC Lenovo ideapad 720S-15IKB
 `+oooooo: Kernel: 6.3.6-arch1-1
 -+oooooo+: Uptime: 6 hours, 59 mins
 `/:-:++oooo+: Packages: 975 (pacman), 8 (flatpak)
 `/++++/+++++++: Shell: bash 5.1.16
 `/++++++++++++++: Resolution: 1920x1080
 `/+++ooooooooooooo/` DE: Plasma 5.27.5
 ./ooosssso++osssssso+` WM: kwin
 .oossssso-````/ossssss+` Theme: [Plasma], Layan-Light-Solid [GTK2/3]
 -osssssso. :ssssssso. Icons: Papirus [Plasma], Papirus [GTK2/3]
 :osssssss/ osssso+++. Terminal: konsole
 /ossssssss/ +ssssooo/- CPU: Intel i5-7300HQ (4) @ 3.500GHz
 `/ossssso+/:- -:/+osssso+- GPU: Intel HD Graphics 630
 `+sso+:-` `.-/+oso: Memory: 7216MiB / 19554MiB
 `++:. `-/+/
 .` `/

经过测试，处理 10 个 .flac 文件所需时间为 59 秒。速度慢的原因是目前使用的是单进程串行的处理方式，为了提高速度，可以同时启动多个进程并行处理。

使用终端工具GNU Parallel，命令如下：

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ls *.flac | parallel -j4 "ffmpeg -i {} -ab 320k -map_metadata 0 -id3v2_version 3 {.}.mp3 && rm {}"

parallel 将从标准输入中读取文件列表，-j 指定了并行进程数，{} 代表输入文件名，{.} 代表没有后缀的输入文件名，其他用法可以 man parallel 查看。

经过测试，在同样环境下处理同样的 .flac 文件仅需 17 秒。