The command will return nothing as the value of thecountrywasn’t set in the first place. If the value of the variable is unset, using the following technique, we can assign a value. $echo${country=Greenland} Here, Bash will check if the variable country has any value stored. As the ...
while [ -n "$var" ] do temp=${var#?} ## everything but the first character char=${var%"$temp"} ## remove everything but the first character : do something with "$char" var=$temp ## assign truncated value to var done 反转 您可以使用相同的方法颠倒字符串中字符的顺序。每个字母都...
tered, an attemptismadetodefine afunctionusing``-f foo=bar'', an attempt is made to assign avaluetoareadonlyvariable, an attemptismadetoassign a valuetoan array variable withoutusingthe compound assignment syntax (see Arrays above), oneofthe namesisnota valid shell variable name, an attempti...
# 也不可以這樣:Variable='Some string'# Bash 會認爲 'Some string' 是一條指令,由於找不到該指令,這裡會再次報錯。# (這個例子中 'Variable=' 這部分會被當作僅對 'Some string' 起作用的賦值。)# 使用變數:echo$Variableecho"$Variable"echo'$Variable'# 當你賦值 (assign) 、匯出 (export),或者以其...
# 也不可以这样：Variable= 'Some string'# Bash 会认为 'Some string' 是一条指令，由于找不到该指令，这里再次报错。# （这个例子中 'Variable=' 这部分会被当作仅对 'Some string' 起作用的赋值。）# 使用变量：echo $Variableecho "$Variable"echo '$Variable'# 当你赋值 (assign) 、导出 (export)，...
You can assign data to a variable using the equals sign (=). The data you store in a variable can either be a string or a number. Let’s create a variable now on the command line: chapter_number=5 The variable name is on the left hand side of the equals sign, and the data whic...
Use Default Values. If parameter is unset ornull, the expansion of word is substituted. Otherwise, the value of parameter is substituted. ${parameter:=word} Assign Default Values. If parameter is unset or null, the expansionof word is assigned to parameter. Thevalue of parameter is ...
Now you are ready to execute your first bash script: ./hello_world.sh 2. Simple Backup bash shell script #!/bin/bash tar -czf myhome_directory.tar.gz /home/linuxconfig 3. Variables In this example we declare simple bash variable and print it on the screen ( stdout ) with echo comman...
echo '$Variable' # 当你赋值 (assign) 、导出 (export),或者以其他方式使用变量时,变量名前不加 $。 # 如果要使用变量的值, 则要加 $。 # 注意: ' (单引号) 不会展开变量(即会屏蔽掉变量)。 # 在变量内部进行字符串代换 echo ${Variable/Some/A} ...
Variable assignments and builtin commands that affect the shell's environment do not remain in effect after the command completes. The return status is the exit status of list. { list; } list is executed in the current shell environment. The list must be terminated with a newline or semi...