宏駿的Linux資訊小站

Variables are named values
useful for storing data or command output
設定變數值：variable=value
取出變數傎：echo $value
如：
[root@localhost ~]# john=$(ls /etc/)
[root@localhost ~]# echo $john
a2ps.cfg a2ps-site.cfg acpi adjtime aliases aliases.db alsa alternatives anacrontab asound.state at.deny audit autofs_ldap_auth.conf auto.master auto.misc auto.net auto.smb avahi bashrc blkid bluetooth bonobo-activation capi.conf cdrecord.conf conman.conf cron.d cron.daily cron.deny cron.hourly cron.monthly crontab cron.weekly csh.cshrc csh.login cups dbus-1 default depmod.d desktop-profiles dev.d DIR_COLORS DIR_COLORS.xterm 
...skip....
[root@localhost ~]# 

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[root@localhost ~]# hi="hello,nice to meet you."
[root@localhost ~]# echo $hi
hello,nice to meet you.
[root@localhost ~]# 

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Configuration variables
PS1：man 1 bash

常用的變數

\h	short hostname
\u	user name
\w	the current working directory
\!	the history number of the current command
\$	shows $

 

PATH： 可執行程式的路徑 
EDITOR： 預設文字編輯器 
HISTFILESIZE: Number of commands in bash history 
資訊變數：
    HOME：使用者目錄
    EUID：使用者有效的UID

[root@localhost ~]# man 1 bash
BASH(1)                                                                BASH(1)

NAME
       bash - GNU Bourne-Again SHell

SYNOPSIS
       bash [options] [file]

COPYRIGHT
       Bash is Copyright (C) 1989-2005 by the Free Software Foundation, Inc.

DESCRIPTION
       Bash  is  an sh-compatible command language interpreter that executes commands read from the
       standard input or from a file.  Bash also incorporates useful features from the Korn  and  C
       shells (ksh and csh).

       Bash  is intended to be a conformant implementation of the IEEE POSIX Shell and Tools speci-
       fication (IEEE Working Group 1003.2).  Bash can be  configured  to  be  POSIX-conformant  by
       default.

OPTIONS
       In  addition  to the single-character shell options documented in the description of the set
       builtin command, bash interprets the following options when it is invoked:

       -c string If the -c option is present, then commands are read from  string.   If  there  are
                 arguments after the string, they are assigned to the positional parameters, start-
                 ing with $0.
       -i        If the -i option is present, the shell is interactive.
       -l        Make bash act as if it had been invoked as a login shell (see INVOCATION below).

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Use aliases let you create shortcuts to command
使用別名可以讓使用者快速和便倢的使用指令
如：
將 ls -la 取別名為dir
[root@localhost ~]# alias dir='ls -la'

此時只要執行 dir 即是執行 "ls -la"
Use alias by itself to see all set aliases
[root@localhost ~]#alias dir
alias dir='ls -la'

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bash Expands a command line

alias 能夠和其他指令混用
curly-brace statements ({}) 
tilde statements (~)
variables ($) 通常用 $ ${} $(()) $[] $() ` 
Expand file globs (*, ?, [abc], etc) 
Prepare I/O redirections (<, >) 
Run the command  ! 

Quoting(\) prevents expansion

 

1. Single quotes (') inhibit all expansion
2. Double quotes (") inhibit all expansion, except:
3. $ (dollar sign) - variable expansion
4. ` (backquotes) - command substitution
5. \ (backslash) - single character inhibition
6.  ! (exclamation point) - history substitution

 

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Bash 執行任務：profile

 

bash執行過程會依序載入這些啟動命令 
儲存在 /etc/profile and ~/.bash_profile 
只有可以登入的 shell 才有作用 
通常用來設定環境變數
Running commands (eg. mail-checker script) 
儲存在 /etc/bashrc and ~/bashrc  

Run for all shells
通常用來Setting 本地端的變數
Defining aliases(別名設定)

Bash 離開時的任務
儲存在 ~/.bash_logout (user) 
在 login shell 離開時執行 
Creating automatic backups 
Cleaning out temporary files 

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取得 input with the read 指令

使用 read to assign input 值  to one or more shell 變數：
-p designates prompt to display 
read reads from standard input and assigns one word to each variable 
Any leftover words are assigned to the last variable 
read -p "Enter a filename: " FILE