recover/undo previous git reset --hard
- use git reflog to show history
- use git reset --hard <hash> to recover the old files
If you want to revert changes made to your working copy, do this: git checkout .
If you want to revert changes made to the index (i.e., that you have added), do this.
- Warning this will reset all of your unpushed commits to master!: git reset
reset --soft a specified file with path git reset <commitid> -- path/to/file
If you want to revert a change that you have committed, do this: (it will generate a new revert commit in git log) git revert <commit 1> <commit 2>
If you want to remove untracked files (e.g., new files, generated files): git clean -f
Or untracked directories (e.g., new or automatically generated directories): git clean -fd
checkout remote branch to local with diff name git checkout -b <local_branch_name> <remote_name>/<remote_branch_name>

Merge / Conflict

fix conflict by accepting others/ours

git checkout --theirs <conflicted_file>
git checkout --ours <conflicted_file>

stash

stash specific files
- git stash -- <file>
speed up clone: git clone https://github.com.cnpmjs.org/xxxxx/xxxxxxx.git
Fatal: Refusing to merge unrelated histories New repo was created via UI with init commit. At the same time, git add at local and with another init commit. When git pull at local, git treats those two as diff trees since they don't have same origin. Solution 1: using git clone to clone repo to local Solution 2: git pull origin [repo] --allow-unrelated-histories

force pull a repo to overwrite local changes

git fetch --all
git reset --hard origin/master
git pull --force # not work if repo has forced push

bisect - Use binary search to find the commit that introduced a bug
- Get good with git: bisect

force overwrite local untracked files

git fetch --all
git reset --hard origin/master

change message of last commit
```
git commit --amend
```

merge multiple commits into one

# approach 1
git reset --soft HEAD~n
git commit --amend
# approach 2
git rebase --interactive HEAD~n
# or
git rebase -i <commit#>
# then should pick ealy commit and squash later commit
git rebase --continue
# push to remote repository forcely
git push origin <branch> --force

edit a pushed commit message

git rebase -i '<commitno>^'
# change pick to be edit, save
git commit --amend
git rebase --continue
git push --force

edit last committed message

git commit --amend
git push --force    # if pushed already

stop tracking a file/directory

git rm [-r] --cached filename/[directory_name] # --cached will keep the removed file locally
or
git update-index --assume-unchanged filename

HTTP github clone on Windows error with message error setting certificate verify locations

git config --system http.sslverify false   # this will switch off the ssl verify for ALL http connections

checkout or pull a folder/file instead of the whole repository

mkdir myrepo
cd myrepo
git init
git remote add -f origin github/aidysun/repo.git
git config core.sparseCheckout true
echo "folder_a/" >> .git/info/sparse-checkout
git pull

roll back specific file

# undeleted files
git checkout <commit> -- path/to/file
# file were deleted and committed
#    1. find the commit deleted the file
git rev-list -n 1 HEAD -- <deleted_file_path>
#    2. checkout to the previous commit of commit deleted the file
git log -- <deleted_file_path>
git checkout <delete_commit>^ -- <deleted_file_path> 
#or
git checkout <before_delete_commit> -- <deleted_file_path>

rollback a specific history commit
- git revert undo the effects of only a certain commit
- git reset is used to undo/delete all commits that came afterwards
```
# rollback to <commit> and force push, ** histories will be deleted in log as well **
git reset --hard <commit>
git push origin master --force
```
- For local changes, rollbace/rebase one commit
- git rebase -i xxxxx^

show history and diff with file names

git log --stat --oneline
git diff --name-only
git log -- file.ext     # by file
git log -p              # print patch, source diff 
git show <commit_no>    # show specific comment
git log --grep="smth"   # filter by message
git shortlog            # group my author

un-stage a file, won't delete from local workspace

git reset -- <file>


this won't actually un-stage a file, it just works for the new files that staged.
it stages the removal file from the repo but leaves the file in your working tree
git rm --cached

rename a tag

git tag new_tag old_tag
git tag -d old_tag
git push origin :refs/tags/old_tag  # this delete tag remotely, another way is git push --delete origin old_tag
git push --tags
# other to get the new tags
git pull --purne --tags

merge a specific commit
```
git cherry-pick <commit_no>
```
Splitting a subfolder out into a new repository
"refusing to merge unrelated histories”
- git pull origin master --allow-unrelated-histories
rename file sensitively on Windows
```
git mv -f Myfile myfile
```
Commit statistics : git shortlog -sn

branch

show all branches

git branch -a  # -r
git branch -vv
git remote show origin
git ls-remote --heads origin

merge/checkout files from another branch

# current branch master
git checkout another_branch ./file1 ./file2

show branch name in bash command prompt

checkout one remote branch to local

git checkout --track origin/branch
# --track is shorthand for -b [local_branch] [remote]/[branch]

git fetch origin anotherBranch:localBranch
git branch
git checkout localBranch

delete remote branch
```
git push origin --delete branch_name
```
force push to remote repository
```
git push origin <branch> --force
```

submodule

add - NOTE: .gitmodules should be committed for tracking
```
git submodule add http....
```

clone / update submodules

when clone

git clone --recurse-submodules https://main-repo

after clone (if --recurse-submodules was forgotten)

git submodule update --init    # which is a combination of following two steps
git submodule init
git submodule update

show submodules status
```
git config status.submodulesummary 1
```

update submodules to latest

git submodule update --init --recursive --remote [subModuleName]
git submodule update --remote     # would update existing submodule to latest

how to remove a submodule

0. mv a/submodule a/submodule_tmp
1. git submodule deinit -f -- a/submodule    
2. rm -rf .git/modules/a/submodule
3. git rm -f a/submodule

Reinit all local submodules / cleanup messed submodules
1. remove all submodules in .git/config
2. empty folder .git/modules/*
3. empty real path of submodules (may refer to the pathes in .gitmodules)
4. git submodule update --init --recursive

.git

shrink huge .git/objects
```
git fsck 
git prune
```

git log

show diff between branches, show differences in branch2 comparing to branch1
```
git log --cherry branch1..branch2
```

tilde(~) caret(^) at-sign(@)

tl;tr;
- ~ : goback on a straight line, one current main branch
- ^ : used on merge commit, HEAD^1 is main branch merged into, HEAD^2 is the side branch merged into main branch.
- @ : used for the git reflog
https://www.golinuxcloud.com/git-head-caret-vs-tilde-at-sign-examples/#:~:text=The%20tilde%20%28~%29%2C%20caret%20%28%5E%29%20and%20at-sign%20%28%40%29,refer%20to%20the%20parent%20of%20that%20particular%20commit.

stash file to patches

git stash list | while read stash; do
    index=$(echo "$stash" | cut -d: -f1 |cut -d'}' -f1 | cut -d'{' -f2)
    echo $index
    git stash show -p "$index" > "stash_$index.patch"
done
# in target repo:
# git apply xxx.patch

Windows

search files by size in Explorer with keywords like * size:>50MB<100MB
Hide cmd window after launching an exe file in a bat/cmd file. Using start command.
```
@echo off
start aaa.exe
```
Outlook rules of same email address with different names
- https://www.msoutlook.info/question/sender-name-contains-specific-text-rule
Manage stored certificates
- Win+R control keymgr.dll
- Control Panel\All Control Panel Items\Credential Manager

turn off terminal bell in subsystem linux

$ sudo vi /etc/inputrc
set bell-style none

Screenshot of current window
```
Win + Alt + PrtSc
```

Path of saved screenshot token with "Win+Shift+S"

C:\Users\<username>\AppData\Local\Packages\Microsoft.Windows.ShellExperienceHost_cw5n1h2txyewy\TempState\ScreenClip

Path of root of WSL Ubuntu from Store

C:\Users\<username>\AppData\Local\Packages\CanonicalGroupLimited.UbuntuonWindows_79rhkp1fndgsc\LocalState

copy multiple files between folders

robocopy \src\dir  \dest\dir  file1.txt file2.pdf

task management in cmd

tasklist /FI "IMAGENAME eq xxx.exe"
taskkill /IM "xxx.exe" /F

Disable Hibernate to free up disk space
- powercfg -h off

check user info and group info

net localgroup [groupname] 
net user username

create directory symbol link

mklink /D [to] [from] 
    /H  creates hard link
    /J  creates a directory junction

run as user
```
runas /user:%USERDOMAIN%\%USERNAME% /savedcert "mklink /D C:/folder D:/folder"
```
- /savedcert requires manually password input for the first run, logoff and login to make it work.

check architecture(x86 x64) of DLL

REM run in Visual Studio Command Prompt
dumpbin /HEADERS <your.dll> | more

determine .lib is static or dynamic

REM run in Visual Studio Command Prompt
lib /list xxx.lib     # xxx.dll - dynamic,   xxx.obj - static

Windows equivalent of wc -l in Batch, find /c /v ""
```
keytool -list | find /c /v ""
```

run cmd from a specific folder in a new window

start /D C:\Users cmd /k echo "Hello world."

Add "Open with Sublime Text 3" to Windows Explorer Context Menu
Visual Studio cleans wrong output directory when clean/rebuild?
- Intermediate Directory - if two platforms share the same intermediate dir, this issue will happen ever they have diff output dir.

Unallocated space in USB flash drive, run diskpart

disk list
select disk 1
clean
clean partition primary

macOS

monitor a program by its name: monitor.sh
Use old build system with Xcode 10 and later : xcodebuild -UseModernBuildSystem=NO -project xxx

Remove download from info:

xattr -r -d com.apple.metadata:kMDItemWhereFroms xxx.zip
xattr -r -d com.apple.quarantine xxx.zip

Sort child folders by size
```
du -hc -d 1 | grep -v "/$" | sort -rh
```
"Your password does not meet the requirements", reset the password policy database:
```
sudo pwpolicy -clearaccountpolicies
```
Storage management
- ~/Library/Caches

if usb of MBR cannot charing iPhone

sudo killall -STOP -c usbd
sudo killall -CONT usbd

add user to group

sudo dseditgroup -o edit -a aidy -t user wheelGroup

lockscreen using command

/System/Library/CoreServices//Menu\ Extras/User.menu/Contents/Resources/CGSession -suspend

show/hide hidden files and directories in Finder

alias showFiles='defaults write com.apple.finder AppleShowAllFiles YES; killall Finder /System/Library/CoreServices/Finder.app'
alias hideFiles='defaults write com.apple.finder AppleShowAllFiles NO; killall Finder /System/Library/CoreServices/Finder.app'

find by name and execute command to results

find . -iname 'xc*data' -exec git rm -r --cached {} \;
# exec two grep commands, the 2nd one is based on 1st one's result
find . -iname "*.ts"  -exec sh -c "grep  -H 'dt.an.13.030' -A 2 {} | grep -H '<translation>' " \;

list exported symbols of shared library
```
nm -a log4cplus
```

Show build settings of Xcode projects

xcodebuild -project myProj.xcodeproj -target "Release_Cocoa64" -showBuildSettings

Quick Look or Preview text files in Finder

# e.g. xml files
sudo  find . -name *.xml -exec SetFile -t TEXT {} ; 
# alternative https://github.com/sindresorhus/quick-look-plugins?? not tried

Cannot find dylib files when adding links in Xcode?
- Using Other Linker Flags instead of selecting, e.g. -liconv instead of libiconv.dylib
- As well as system frameworks (e.g. -framework IOKit)

hostname

scutil --get LocalHostName
sudo scutil --set HostName new.host.name
hostname

enable built-in VNC control of macOS Mojave (10.14) when remoting desktop using VNC client
1. Open System Preferences -> Security & Privacy -> Privacy -> Accessibility
2. In Finder, navigate to /System/Library/CoreServices/RemoteManagement/AppleVNCServer.bundle/Contents/MacOS/AppleVNCServer
3. Add AppleVNCServer to granted list.

change default location to store screenshots

defaults write com.apple.screencapture location ~/Pictures/screenshots/

mount writable NTFS hard disk

0. plug NTFS usb
1. sudo nano /etc/fstab
2. LABEL=NAME none ntfs rw,auto,nobrowse
3. Ctrl+O
4. remove NTFS usb and reconnect it
5. ls /Volumes

Accessing Grayed-out Preference Panes
- Duplicate System Preferences.app, and delete NSPrefPaneGroups.xml.
Useful commands from linux
- ulimit -a, at, cron

Markdown

how to add page break in Markdown

<div style="page-break-after: always"></div>

bookmark

<a name="link_name">content to show</a>
...
[reference](#link_name)

Paste to Markdown

Shell

replace text content recursively

find . -type f -name "config" -exec sed -i 's/aaa/bbb/g' {} \;

sort file by size: du -h -d 1 | sort -h -r

rename files/directories by regexp with find command (checked on Ubuntu)

find . -type f -name "*OldFileName*" -exec rename -v 's/OldFile/new_file/' {} \;

diff
- diff a.txt b.txt # normal diff
  - 3c3: 3-line num, c-change (d-delete, a-addition), 3-line number
  - <: delete, >: add
- diff -c a.txt b.txt # context diff
- diff -u a.txt b.txt # unified diff
margin setting for Ubuntu terminal : https://askubuntu.com/questions/115762/increase-padding-in-gnome-terminal
compare folders
```
diff -rq folder1 folder2
```

rename files/folders with regex replacement

# rename files contain "2017" to be "2018" 
for f in *; do echo  mv "$f" "${f/2017/2018}"; done

screen - multiple session in one terminal, especially useful for linux terminal

screen -ls
screen -r xx # restore/reattach
C-a w   / C-a "  # list all
C-a n     # next
C-a C-a
C-a 0..9
C-a '
C-a k    # close current window in screen

.screenrc

vbell on
vbell_msg ''   # turn off wuff----wuff----!
termcapinfo * vb=:   # set flash to a empty string

reload screenrc without restarting screen : Ctrl+a : source /etc/screenrc

why prefer $() to ` `
- because $() can be nested
- it doesn't need to escape

prefer [[]] to []

[ "${name}" \> "a" -o "${age}" \< "20"]   # using []
[[ "${name}" > "a" && "${age}" < "20"]]   # using [[]]

bash options

#!/bin/bash
set -o nounset
set -o errexit
...

redirection in shell
- 0: stdin, 1: stdout, 2: stderr
```
ls a.txt b.txt > output.txt 2> error_output.txt
ls a b c > all_output.txt 2>&1
```
  - >& redirects one out data stream to another
- capture command output to file while alos viewing it live more
```
command |& tee file.txt
```
Turn on ANSI color in Terminal, add following lines in ~/.profile
```
export CLICOLOR=1
export LSCOLORS=GxFxCxDxBxegedabagaced
```

show branch name in bash command prompt

function git_branch() {
    git branch 2>/dev/null | sed -e '/^[^*]/d' -e 's/* \(.*\)/ (\1)/'
}

export PS1="\n\[\e[1;33m\]\t \[\e[1;32m\]\w\[\e[0;33m\] $(git_branch) \n\[\e[1m\]\[\e[0;32m\]>>> \$ \[\e[0m\]"

copy files to local system via SSH

scp -r username@10.1.1.1:~/Downloads/folder ~/Downloads

default parameter value

set var1 = ${1:-default} # set var1 to be 'default' if $1 is not set
set var2 = ${VARIABLE2:-empty} # set var2 to be 'empty' if $VARIABLE2 is not set

prompt for user input

read -p "input a word: " inputtedVar
echo $inputtedVar

auto input for prompt/password

expect <<- DONE
spawn scp $1 user@192.168.1.1:/work/
expect "password:"
send -- "mypassword\r"
#interactive
expect eof
DONE

xargs - each line as a parameter to a cmd
```
cat file.txt | xargs -L1 <cmd>
```
replacing all line breaks
```
sed ":a;N;$!ba;s/\n/,/g' file
```

Vim

insert continus index to starting of lines
```
:%s/^/\=line('.').'.'
```
- add 1, 2, 3, from line 10 to line 88 : 10,88s/^/\=line('.')-9.'.'
case [in-]sensitive search with \c: E.g. /InSensitive\c

Hide vim to background

# in vim
Ctrl+z
# then, return to vim
fg

vim color scheme

# color themes locate in /usr/shared/vim/vim80/colors/
# in ~/.vimrc
colorscheme industry

Key mappings

// imap: insert mode, <c-d>:ctr+d, <esc>ddi: key in order 
:map - x
:imap <c-d> <esc>ddi
:let mapleader = "-"
:vmap <leader>\ U
// no remap
:inoremap <c-d>
// unmap
:nunmap -

Adjust the split window size

:ctr+w _ " max height
:ctr+w | " max width
:ctr+w = " equal size

Open multiple files with split windows
```
$ vim -o[O] file1 file2 ...
```

Scroll screen without changing cursor

zz " move current line to middle of screen
zt " move current line to top of screen
zb " move current line to bottom of screen

others

.        " repeat last action
:e!      " restore to doc origin
I        " insert at first non-space
A        " insert at end of the line
:n1,n2 w [filename]    " save lines n1~n2 as

Plugin
- https://github.com/junegunn/vim-plug/wiki/tutorial
- https://github.com/peterhoeg/vim-qml

tabs

open multiple files in diff tabs: vi -p f1.txt f2.txt

navigation between tabs:

command mode:

:tabn # go to next tab
:tabp # go to previous tab
:tabnew # create a new tab
:tabclose # close a new tab
:tabclose {i} # close the tab in postion {i}
:tabe {file} # edit in new tab
:tabfirst # go to first
:tabm 0  # move to first

normal mode:

gt    # go to next tab
gT    # go to previous tab
{i}gt # go to tab in position i

Python

Install packages in Jupyter Notebook

import sys
!conda install pip
!python -m pip install keras

Location of installed package: pip show <package_name>
Installed packages: pip list

platform

import platform
print(platfrom.platform())
print(platfrom.python_version())

Chrome

Download CRX extension
- https://clients2.google.com/service/update2/crx?response=redirect&prodversion=[PRODVERSION]&acceptformat=crx2,crx3&x=id%3D[EXTENSIONID]%26uc
  - [PRODVERSION] is the version of Chrome, which must be 31.0.1609.0 at the very least
  - [EXTENSIONID] is the ID of the extension

Ubuntu

force to relaod ~/.tmux.conf
```
# in tmux
tmux kill-server
```

List installed packages

apt list --installed
dpkg --get-selections

show hidden folders Ctrl+H - tried on CentOS
what if python was removed from system
- Ctrl+Alt+F4 to enter terminal
- sudo apt-get install ubuntu-minimal ubuntu-standard ubuntu-desktop
- sudo reboot
- startx

pip does not work after upgrade, it says ImportError: cannot import name 'main'

sudo python[3] -m pip uninstall pip && sudo apt install python3-pip --reinstall
pip3 # or
python3 -m pip

CentOS

how to change libc.so.6 link? Do not try to rm it and recreate the link
```
ldconfig -l -v /lib64/libc-2.30.so
```

Java

JVM status check

jps -v
jstat -gc <jvmid>
jmap -heap <jvmid>
jmap -histo:live <jvmid> | more

Get JNI method signature from java class
```
javap -s a.class
```
Eclipse cannot connect to Marketplace (from China)
- add following content to eclipse.ini (in Eclipse.app on macOS)
```
 -Djava.net.preferIPv4Stack=true 
```
Chrome Selenium WebDriver cannot perform another action before previous action finishes
- tried executeAsyncScript, sendKeys, click() and Selenium IDE recording, no one worked
- final solution was to use onclick function of web element

Reset Eclipse Color and Fonts to Default

rm <workspace/.metadata/.plugins/org.eclipse.core.runtime/.settings

CPP

Since C++11, unique_ptr supports dynamic array, but not shared_ptr
```
std::unique_ptr<int[]> p(new int[nsize]); // type is int[]
```

XPath

Samples
- //table[class='table-class']//td[contains(text(),'row1']/following-sibling::td[text()='column 2']
- //div[@alt='This is a img' and @class='img-class']

VMWare

Shortcut to escape VM (on Windows): Ctrl+Alt
- Switch back to vmware with Alt+Tab then Ctrl+g

JIRA

search multiple version with wildcard *: versionMatches("v1.*")
- issuetype = Bug AND affectedVersion IN versionMatches("5.15.*") AND text ~ "binding broken"

UML

Class relationship

extension : <|--
composition : *--
aggregration : o--

Composition v.s. Aggregation

Composition
- Composite aggregation is a subtype of aggregation relation with characteristics as:
  - It is a two-way association between the objects.
  - It is a whole/part relationship.
  - If a composite is deleted, all other parts associated with it are deleted.
- The folder could contain many files, while each File has exactly one Folder parent. If a folder is deleted, all contained files are removed as well.
- Folder "1" *-- "many" File
Aggregation
- Let us consider an example of a car and a wheel.
- A car needs a wheel to function correctly, but a wheel doesn't always need a car. It can also be used with the bike, bicycle, or any other vehicles but not a particular car. Here, the wheel object is meaningful even without the car object. Such type of relationship is called UML Aggregation relation.
- Car "1" o-- "many" Wheel : aggregation

Regexp

search words not included: (?!notincludeword), (?!word\b)
search two words accross multiple lines: (?:\n.*?){0,2}
- (?:\n.*?) match anything including line break
- {0,2} match times range
- e.g. search for class....data at most 22 lines
```
(class.\{)(?:\n.*?){1,22}data
```

online tool

Opensource

How to design a version-compatible library
- https://ometer.com/parallel.html

AidySun/dev_tips

TOC

Git

show size info of a history file

checkout/reset/revert/clean