Miles' Blog

天涯何處無幹話，何必要講實務話

Variable

All System Variables

env

User Defined Variables

# 等號兩邊不能直接接空白字元
myhome="/home/v/vivek"

echo "$myhome"
# or
echo "${myhome}"

指令

version=$(uname -r)
# or
version=`uname -r`

echo $version

Built-in shell variables

Variable 	Use
$? 	  the exit value of the last command that was executed.
$# 	  the number of command-line arguments that were passed to the shell program.
$* 	  all the arguments that were entered on the command line ($1 $2 ...).
$@ 	  all the arguments that were entered on the command line, individually quoted ("$1" "$2" ...).
$0 	  the first word of the entered command (the name of the shell program).

e.g.

./command -yes -no /home/username
  • $# = 3
  • $* = -yes -no /home/username
  • $@ = array: {“-yes”, “-no”, “/home/username”}
  • $0 = ./command
  • $1 = -yes

Delete

# 基本的用法

$(variable#string)
  • variable 是變數名
  • string 是欲刪除的字串，可以搭配萬用字元 ? * 使用

實際的作用是：由左至右，刪除符合字串中最短的那一個（因為有萬用字元）

舉例：

SOME_FILE=some_file.png
ANOTHER_FILE=another${SOME_FILE#some}

echo ${ANOTHER_FILE}
# See 'another_file.png'

% 則是相反

舉例：

PNG_FILE=somefile.png
SVG_FILE=${PNG_FILE%.png}.svg

echo ${SVG_FILE}
# See 'somefile.svg'

Replace

References

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