條件測試
test 命令
一．測試文件
一般形式：
1． test condition
2． [ condition ]
文件狀態 ，例如 test –d name 或者 [ -d name ]
|
-d |
目錄 |
-s |
文件長度大於 0 ，非空 |
|
-f |
正規文件 |
-w |
可寫 |
|
-L |
符號鏈接 |
-u |
文件有 suid 位設置 |
|
-r |
可讀 |
-x |
可執行 |
$ test –d name
$ $?
$ 0
0 表示成功， 1 表示返回錯誤
$? 退出最後狀態命令，用來檢查測試結果；
二．測試時使用的邏輯符號
-a 邏輯與
-o 邏輯或
！邏輯否
例如
$ [ -w name1 –a –w name2 ]
$ $?
$ 0
三．測試字符串
一般形式：
test “string”
test string_operator “string”
test “string” string_operator “string”
[string_operator string ]
[string string_operator string]
string_operator ：
|
= |
兩個字符串相等 |
-z |
空串 |
|
!= |
兩個字符串不相等 |
-n |
非空串 |
四．測試數值
一般形式
“number” mumeric_operator “number”
[ “number” mumeric_operator “number” ]
mumeric_operator :
|
-eq |
數值相等 |
-lt |
第一個數小於第二個 |
|
-ne |
數值不相等 |
-le |
第一個數小於等於第二個 |
|
-gt |
第一個數大於第二個 |
-ge |
第一個數大於等於第二個 |
例如
$ a=130
$ b=120
$ [ “$a” –lt “$b” ]
$ echo $?
$ 1
可以使用邏輯操作符
如：
$ [ “990” –le “995” ] –a [ “123” –ge “124” ]
$ echo $?
$ 1
五． expr 命令測試執行和執行數值輸出
一般用於整數值或者字符串
一般形式
expr argument operator argument
expr 也是手工命令行計數器
$ expr 10 + 10
20
減法 – 除法 / 乘法 /*
1. 增量技術
expr 用於增量計算
$ LOOP=0
$ LOOP=`expr $LOOP + 1`
2. $ value=100
$ expr $value + 10 >/dev/null 2>&1
$ echo $?
0
表示是個數值
$ value=hello
$ expr $value + 10 >/dev/null 2>&1
$ echo $?
3
表示是個非數值符號
3. 模式匹配
字符串匹配操作
$ expr $calue : `/(.*/).txt`
Hdisk.txt
在shell中的應用 循環計數
#!/bin/sh
counter=0
for files in *
do
counter=`expr $counter + 1`
done
echo "There are $counter files in `pwd` we need to process"
整數比較
|
-eq |
等於 |
if [ "$a" -eq "$b" ] |
|
-ne |
不等於 |
if [ "$a" -ne "$b" ] |
|
-gt |
大於 |
if [ "$a" -gt "$b" ] |
|
-ge |
大於等於 |
if [ "$a" -ge "$b" ] |
|
-lt |
小於 |
if [ "$a" -lt "$b" ] |
|
-le |
小於等於 |
if [ "$a" -le "$b" ] |
|
< |
小於(需要雙括號) |
(("$a" < "$b")) |
|
<= |
小於等於(需要雙括號) |
(("$a" <= "$b")) |
|
> 大於 |
(需要雙括號) |
(("$a" > "$b")) |
|
>= |
大於等於(需要雙括號) |
(("$a" >= "$b")) |
字符串比較
|
= |
等於 |
if [ "$a" = "$b" ] |
|
== |
等於 |
if [ "$a" == "$b" ],與=等價 注意:==的功能在[[]]和[]中的行爲是不同的,如下: |
|
[[ $a == z* ]] |
# 如果$a 以"z"開頭(模式匹配)那麼將爲true |
|
[[ $a == "z*" ]] |
# 如果$a 等於z*(字符匹配),那麼結果爲true |
|
[ $a == z* ] |
# File globbing 和word splitting 將會發生 |
|
[ "$a" == "z*" ] |
# 如果$a 等於z*(字符匹配),那麼結果爲true |
|
!= |
不等於 |
if [ "$a" != "$b" ] |
|
< |
小於,在ASCII 字母順序下.如:if [[ "$a" < "$b" ]]if [ "$a" /< "$b" ] |
|
|
注意:在[]結構中"<"需要被轉義. |
|
> |
大於,在ASCII 字母順序下.如:if [[ "$a" > "$b" ]]if [ "$a" /> "$b" ] |
|
|
注意:在[]結構中">"需要被轉義. |
|
-z |
字符串爲"null".就是長度爲0. |
|
-n |
字符串不爲"null" |
For Mathematics, use following operator in Shell Script
|
Mathematical Operator in Shell Script |
Meaning |
Normal Arithmetical/ Mathematical Statements |
But in Shell |
|
|
|
|
|
For test statement with if command |
For [ expr ] statement with if command |
|
-eq |
is equal to |
5 == 6 |
if test 5 -eq 6 |
if [ 5 -eq 6 ] |
|
-ne |
is not equal to |
5 != 6 |
if test 5 -ne 6 |
if [ 5 -ne 6 ] |
|
-lt |
is less than |
5 < 6 |
if test 5 -lt 6 |
if [ 5 -lt 6 ] |
|
-le |
is less than or equal to |
5 <= 6 |
if test 5 -le 6 |
if [ 5 -le 6 ] |
|
-gt |
is greater than |
5 > 6 |
if test 5 -gt 6 |
if [ 5 -gt 6 ] |
|
-ge |
is greater than or equal to |
5 >= 6 |
if test 5 -ge 6 |
if [ 5 -ge 6 ] |
For string Comparisons use
|
Operator |
Meaning |
|
string1 = string2 |
string1 is equal to string2 |
|
string1 != string2 |
string1 is NOT equal to string2 |
|
string1 |
string1 is NOT NULL or not defined |
|
-n string1 |
string1 is NOT NULL and does exist |
|
-z string1 |
string1 is NULL and does exist |
Shell also test for file and directory types
|
Test |
Meaning |
|
-s file |
Non empty file |
|
-f file |
Is File exist or normal file and not a directory |
|
-d dir |
Is Directory exist and not a file |
|
-w file |
Is writeable file |
|
-r file |
Is read-only file |
|
-x file |
Is file is executable |
Logical Operators
Logical operators are used to combine two or more condition at a time
|
Operator |
Meaning |
|
! expression |
Logical NOT |
|
expression1 -a expression2 |
Logical AND |
|
expression1 -o expression2 |
Logical OR |
