標籤:welcome 使用者登入
37.調整變數的屬性
38.自訂環境變數
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以系統管理員的角色工作時,環境變數設定檔有三個
/etc/profile
/etc/bash.bashrc
/etc/skel目錄下的所有檔案
39.Here Document
基本用法:
[[email protected] ~]# cat >>123.txt<< end> hello > my name is "jack"> welcome to BJ> endYou have new mail in /var/spool/mail/root[[email protected] ~]# cat 123.txt hello my name is "jack"welcome to BJ
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[[email protected] ~]# Wow=‘Wow,great!‘[[email protected] ~]# m1=$(cat <<HERE> line 1 is good.> They are jack,marry and john.> $WoW> HERE> )[[email protected] ~]# echo $m1line 1 is good. They are jack,marry and john.
[[email protected] ~]# m1=$(cat <<‘HERE‘> line 1 is good.> They are jack,marry and john.> $WoW> HERE> )[[email protected] ~]# echo $m1line 1 is good. They are jack,marry and john. $WoW
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40.如何測試變數是否存在
文法: ${待測變數-預設值}
解釋:判斷待測變數是否存在,如果變數存在,就傳回變數的值,如果沒有就會將預設值傳給待測變數
[[email protected] ~]# unset myname[[email protected] ~]# r=${myname-‘basher‘}[[email protected] ~]# echo $rbasher
[[email protected] ~]# myname="Jack"[[email protected] ~]# r=${myname-‘basher‘}[[email protected] ~]# echo $rJack
[[email protected] ~]# myname=[[email protected] ~]# r=${myname:-‘basher‘}[[email protected] ~]# echo $rbasher[[email protected] ~]# unset myname[[email protected] ~]# r=${myname:-‘basher‘}[[email protected] ~]# echo $rbasher
文法:${待測變數:?提示資訊}
解釋:判斷變數是否"不存在"或者為"空",如果條件成立,則顯示:?後的提示資訊。並立即停止執行script
拆解運算式:
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範例:
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本文出自 “Linux革命” 部落格,請務必保留此出處http://kaibinyuan.blog.51cto.com/7304008/1612017
Shell理論學習(三)