前言
在git中如果想忽略掉某个文件，不让这个文件提交到版本库中，可以使用修改根目录中 .gitignore 文件的方法（如果没有这个文件，则需自己手工建立此文件）
正文
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Git忽略规则：
#此为注释 – 内容被 Git 忽略
.sample # 忽略所有 .sample 结尾的文件
!lib.sample # 但 lib.sample 除外
/TODO # 仅仅忽略项目根目录下的 TODO 文件，不包括 subdir/TODO
build/ # 忽略 build/ 目录下的所有文件
doc/.txt # 会忽略 doc/notes.txt 但不包括 doc/server/arch.txt
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.gitignore规则不生效的解决办法
把某些目录或文件加入忽略规则，按照上述方法定义后发现并未生效，原因是.gitignore只能忽略那些原来没有被追踪的文件，如果某些文件已经被纳入了版本管理中，则修改.gitignore是无效的。那么解决方法就是先把本地缓存删除（改变成未被追踪状态），然后再提交：
git rm -r --cached .
git add .
git commit -m 'update .gitignore'
下面是Keil工程的例子
/Project/Listing
/Project/Output
/Project/Pro
*.bin
PLC.*
PLC.PO
PLC.PS
PLC.SearchResults
PLC.WK3
下面是iOS .gitignore内容的一个示例
#
# gitignore contributors: remember to update Global/Xcode.gitignore, Objective-C.gitignore & Swift.gitignore
## Build generated
build/
DerivedData/
## Various settings
*.xcuserstate
*.DS_Store
*.pbxuser
!default.pbxuser
*.mode1v3
!default.mode1v3
*.mode2v3
!default.mode2v3
*.perspectivev3
!default.perspectivev3
xcuserdata/
## Other
*.moved-aside
*.xccheckout
*.xcscmblueprint
## Obj-C/Swift specific
*.hmap
*.ipa
*.dSYM.zip
*.dSYM
# CocoaPods
#
# We recommend against adding the Pods directory to your .gitignore. However
# you should judge for yourself, the pros and cons are mentioned at:
# https://guides.cocoapods.org/using/using-cocoapods.html#should-i-check-the-pods-directory-into-source-control
#
# Pods/
# Carthage
#
# Add this line if you want to avoid checking in source code from Carthage dependencies.
# Carthage/Checkouts
Carthage/Build
# fastlane
#
# It is recommended to not store the screenshots in the git repo. Instead, use fastlane to re-generate the
# screenshots whenever they are needed.
# For more information about the recommended setup visit:
# https://docs.fastlane.tools/best-practices/source-control/#source-control
fastlane/report.xml
fastlane/Preview.html
fastlane/screenshots
fastlane/test_output
# Code Injection
#
# After new code Injection tools there's a generated folder /iOSInjectionProject
# https://github.com/johnno1962/injectionforxcode
iOSInjectionProject/