All System Variables
envUser 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 $versionBuilt-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'