shell技巧分享（三）

這是一個系列文章，主要分享shell（部分功能僅適用於bash）的使用建議和技巧，每次分享3點，希望你能有所收穫。

1 交互模式時自動輸入

$ pip uninstall redis
Uninstalling redis-2.10.6:
  /usr/lib/python2.7/site-packages/redis-2.10.6.dist-info/DESCRIPTION.rst
  /usr/lib/python2.7/site-packages/redis-2.10.6.dist-info/INSTALLER
  /usr/lib/python2.7/site-packages/redis-2.10.6.dist-info/METADATA
  /usr/lib/python2.7/site-packages/redis-2.10.6.dist-info/RECORD
  /usr/lib/python2.7/site-packages/redis-2.10.6.dist-info/WHEEL
  /usr/lib/python2.7/site-packages/redis-2.10.6.dist-info/metadata.json
  /usr/lib/python2.7/site-packages/redis-2.10.6.dist-info/top_level.txt
  /usr/lib/python2.7/site-packages/redis/__init__.py
  /usr/lib/python2.7/site-packages/redis/__init__.pyc
  /usr/lib/python2.7/site-packages/redis/_compat.py
  /usr/lib/python2.7/site-packages/redis/_compat.pyc
  /usr/lib/python2.7/site-packages/redis/client.py
  /usr/lib/python2.7/site-packages/redis/client.pyc
  /usr/lib/python2.7/site-packages/redis/connection.py
  /usr/lib/python2.7/site-packages/redis/connection.pyc
  /usr/lib/python2.7/site-packages/redis/exceptions.py
  /usr/lib/python2.7/site-packages/redis/exceptions.pyc
  /usr/lib/python2.7/site-packages/redis/lock.py
  /usr/lib/python2.7/site-packages/redis/lock.pyc
  /usr/lib/python2.7/site-packages/redis/sentinel.py
  /usr/lib/python2.7/site-packages/redis/sentinel.pyc
  /usr/lib/python2.7/site-packages/redis/utils.py
  /usr/lib/python2.7/site-packages/redis/utils.pyc
Proceed (y/n)? y
  Successfully uninstalled redis-2.10.6
$ pip install redis
Collecting redis
  Using cached redis-2.10.6-py2.py3-none-any.whl
Installing collected packages: redis
Successfully installed redis-2.10.6
$ echo y | pip uninstall redis
Uninstalling redis-2.10.6:
  /usr/lib/python2.7/site-packages/redis-2.10.6.dist-info/DESCRIPTION.rst
  /usr/lib/python2.7/site-packages/redis-2.10.6.dist-info/INSTALLER
  /usr/lib/python2.7/site-packages/redis-2.10.6.dist-info/METADATA
  /usr/lib/python2.7/site-packages/redis-2.10.6.dist-info/RECORD
  /usr/lib/python2.7/site-packages/redis-2.10.6.dist-info/WHEEL
  /usr/lib/python2.7/site-packages/redis-2.10.6.dist-info/metadata.json
  /usr/lib/python2.7/site-packages/redis-2.10.6.dist-info/top_level.txt
  /usr/lib/python2.7/site-packages/redis/__init__.py
  /usr/lib/python2.7/site-packages/redis/__init__.pyc
  /usr/lib/python2.7/site-packages/redis/_compat.py
  /usr/lib/python2.7/site-packages/redis/_compat.pyc
  /usr/lib/python2.7/site-packages/redis/client.py
  /usr/lib/python2.7/site-packages/redis/client.pyc
  /usr/lib/python2.7/site-packages/redis/connection.py
  /usr/lib/python2.7/site-packages/redis/connection.pyc
  /usr/lib/python2.7/site-packages/redis/exceptions.py
  /usr/lib/python2.7/site-packages/redis/exceptions.pyc
  /usr/lib/python2.7/site-packages/redis/lock.py
  /usr/lib/python2.7/site-packages/redis/lock.pyc
  /usr/lib/python2.7/site-packages/redis/sentinel.py
  /usr/lib/python2.7/site-packages/redis/sentinel.pyc
  /usr/lib/python2.7/site-packages/redis/utils.py
  /usr/lib/python2.7/site-packages/redis/utils.pyc
Proceed (y/n)?   Successfully uninstalled redis-2.10.6

有時候執行命令會進入交互模式，需要根據輸入作出不同響應。如果我們提前知道需要輸入的字符沒有風險，那麼可以通過echo命令將字符直接傳遞給命令，避免進入交互模式耽擱時間。比如示例中通過pip命令卸載redis包時，就會讓用戶輸入y或者n，然後根據輸入進行下一步操作。藉助echo命令，可以避免進入交互模式，命令快速執行完畢。再次提醒，前提是你知道輸入的字符沒有風險，比如不要隨便給rm命令echo一個y。

2 運行c代碼

$ cat helloworld.c

#include <stdio.h>

int main ()
{
    printf("hello world!\n");
    return 0;
}
$ gcc helloworld.c -o helloworld
$ ./helloworld
hello world!
$ ls | grep helloworld
helloworld
helloworld.c
$ crn helloworld.c
hello world!
$ ls | grep helloworld
helloworld
helloworld.c

定義的crn函數如下：

crn(){
    gcc $* -g;
    if [ $? -ne 0 ]; then
        echo "failed to build $1"
    else
        ./a.out
        rm -rf ./a.out
    fi
}

在linux命令行，要運行一個c程序，需要先編譯c代碼，然後才能運行該程序。使用go語言運行go代碼時，發現go可以直接運行源代碼，於是有所啓示，我定義一個crn函數，該函數參數是c源代碼文件，crn命令會先編譯c代碼，然後執行編譯後的可執行程序，執行完畢後將可執行程序刪除，省去了編譯環節，更加快速的執行c源程序。例如示例中，執行crn helloworld.c命令就可以運行該c源代碼，確實方便不少。

3 解壓常見格式的壓縮包

ltar(){
if [ -f $1 ]; then
case $1 in
    *.tar.bz2) tar xjf $1;;
    *.tar.gz) tar zxvf  $1;;
    *.bz2) bunzip2 $1 ;;
    *.rar) unrar e $1 ;;
    *.gz) gunzip $1 ;;
    *.tar) tar xf $1 ;;
    *.tbz2) tar xjf $1 ;;
    *.tgz) tar xzf $1 ;;
    *.zip) unzip $1 ;;
    *.Z) uncompress $1 ;;
    *.7z)7z x $1 ;;
    *) echo "'$1' cannot be extracted";;
esac
else
    echo "'$1' is not a valid file"
fi
}

$ ls
gz_file.tar.gz  tar_file.tar
$ ltar tar_file.tar
$ ltar gz_file.tar.gz

日常工作中，經常需要解壓不同格式的壓縮包，但是壓縮格式有很多種，每種壓縮格式的解壓選項和命令行有可能不一樣，要記住那麼多解壓命令和選項實在不容易。通過定義一個函數ltar，將常見壓縮格式文件的解壓命令都封裝在該函數內部，實現一鍵解壓，例如示例中執行ltar tar_file.tar命令和ltar gz_file.tar.gz命令都能解壓相應的壓縮文件。