if 語句包括 字串測試，檔案測試，數字測試
基本的語法為
if test command
then
elsefi或
if [ command ]
then
else
fitest的用法等價於[ ]
例如：if test "hello" = "hello" 與 if [ "hello" = "hello" ] 等價
注意：[ 與 "hello" 與 = 與 "hello" 與 ] 之間存在 空格
1, 下面舉上乙個字串測試的小例子
#字串比較
#!/bin/bash
if [ "hello" = "hello" ]
then
echo "hello" == "hellohello"
else
echo "hello" != "hello"
fiif [ "hell0" = "hell0" ]
then
echo "hell0" == "hello"
else
echo "hell0" != "hello"
fi-z 代表字串為空
-n 代表字串大於0
# shell_if_file 檔案測試
#!/bin/bash
#判斷是否有可執行許可權
if [ -x ./file_test ]
then
echo "is -x"
else
echo "isn't -x"
fi#判斷是否為普通檔案
if [ -f ./file_test ]
then
echo "is general"
else
echo "isn't general"
fi其中：-x 是判斷是否有可執行許可權， -f 是判斷是否為普通檔案
3, 下面為數字測試的小例子， -eq代表相等, -ne代表不等, -lt 代表小於, -le 代表小於等於, -gt 代表大於, -ge 代表大於等於
# shell_if_number 數字比較
#!/bin/bash
echo "please input number1:"
read number1
echo "please input number2"
read number2
#判斷相等
if test "$number1" -eq "$number2"
then
echo "number1 == number2"
else
echo "number1 != number2"
fiecho "please input number1:"
read number1
echo "please input number2"
read number2
#判斷不等
if test "$number1" -ne "$number2"
then
echo "number1 != number2"
else
echo "number1 == number2"
fiecho "please input number1:"
read number1
echo "please input number2"
read number2
#小於if test "$number1" -lt "$number2"
then
echo "number1 < number2"
else
echo "number1 isn't < number2"
fiecho "please input number1:"
read number1
echo "please input number2"
read number2
#小於等於
if test "$number1" -le "$number2"
then
echo "number1 <= number2"
else
echo "number1 isn't <= number2"
fiecho "please input number1:"
read number1
echo "please input number2"
read number2
#大於if test "$number1" -gt "$number2"
then
echo "number1 > number2"
else
echo "number1 isn't > number2"
fiecho "please input number1:"
read number1
echo "please input number2"
read number2
#大於等於
if test "$number1" -ge "$number2"
then
echo "number1 >= number2"
else
echo "number1 isn't >= number2"
fi
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