Tutorial

一旦为Shell变量分配了值,便会创建它们。变量可以包含数字,字符或字符串。变量名区分大小写,可以由字母和下划线“ _”组成。 值分配使用“ =”符号完成。请注意,初始化变量时,=符号的两侧均不允许有空格。

PRICE_PER_APPLE=5
MyFirstLetters=ABC
greeting='Hello        world!'

引用变量

反斜杠“ \”用于转义特殊字符的含义

PRICE_PER_APPLE=5
echo "The price of an Apple today is: \$HK $PRICE_PER_APPLE"

使用$ {}封装变量名可避免歧义

MyFirstLetters=ABC
echo "The first 10 letters in the alphabet are: ${MyFirstLetters}DEFGHIJ"

用“”封装变量名将保留所有空格值

greeting='Hello        world!'
echo $greeting" now with spaces: $greeting"

可以使用命令输出的值来分配变量。这称为替代。可以通过用``(称为反引号)或$()封装命令来完成替换

FILELIST=`ls`
FileWithTimeStamp=/tmp/my-dir/file_$(/bin/date +%Y-%m-%d).txt

请注意,脚本运行时,它将在$()括号内运行命令并捕获其输出。

Exercise

本练习的目标是使用命令替换来创建字符串,整数和复杂变量。该字符串应命名为BIRTHDATE,并且应包含文本“ 2000年1月1日”。该整数应命名为Presents,并应包含数字10。复杂变量应命名为BIRTHDAY,并且应包含与变量BIRTHDATE中的日期匹配的日期的星期几,例如星期六。请注意,“ date”命令可用于将日期格式转换为其他日期格式。例如,要将日期值$ date1转换为date1的星期几,请使用:

date -d "$date1" +%A

Tutorial Code

#!/bin/bash
# Change this code
BIRTHDATE=
Presents=
BIRTHDAY=


# Testing code - do not change it

if [ "$BIRTHDATE" == "Jan 1, 2000" ] ; then
    echo "BIRTHDATE is correct, it is $BIRTHDATE"
else
    echo "BIRTHDATE is incorrect - please retry"
fi
if [ $Presents == 10 ] ; then
    echo "I have received $Presents presents"
else
    echo "Presents is incorrect - please retry"
fi
if [ "$BIRTHDAY" == "Saturday" ] ; then
    echo "I was born on a $BIRTHDAY"
else
    echo "BIRTHDAY is incorrect - please retry"
fi

Expected Output

BIRTHDATE is correct, it is Jan 1, 2000
I have received 10 presents
I was born on a Saturday

Solution

#!/bin/bash
# Change this code
BIRTHDATE="Jan 1, 2000"
Presents=10
BIRTHDAY=`date -d "$BIRTHDATE" +%A`


# Testing code - do not change it

if [ "$BIRTHDATE" == "Jan 1, 2000" ] ; then
    echo "BIRTHDATE is correct, it is $BIRTHDATE"
else
    echo "BIRTHDATE is incorrect - please retry"
fi
if [ $Presents == 10 ] ; then
    echo "I have received $Presents presents"
else
    echo "Presents is incorrect - please retry"
fi
if [ "$BIRTHDAY" == "Saturday" ] ; then
    echo "I was born on a $BIRTHDAY"
else
    echo "BIRTHDAY is incorrect - please retry"
fi