基本傳參

基本應(yīng)用如下：

[test@localhost ~]$ cat var1_test.sh 
#!/bin/bash
echo 參數(shù)0:$0
echo 參數(shù)1:$1
echo 參數(shù)2:$2
echo 參數(shù)3:$3
[test@localhost ~]$ sh var1_test.sh 1 2 3
參數(shù)0:var1_test.sh
參數(shù)1:1
參數(shù)2:2
參數(shù)3:3
[test@localhost ~]$

shell中參數(shù)處理相關(guān)說明：

$*與$@區(qū)別

• 相同點(diǎn)：都是引用所有變量
• 不同點(diǎn)：只有在雙引號(hào)中提現(xiàn)出來。假設(shè)在腳本運(yùn)行時(shí)寫了三個(gè)參數(shù)1嗦随、2列荔、3，則"*"等價(jià)于"1 2 3"（傳遞了一個(gè)參數(shù)）枚尼，而"@"等價(jià)于"1" "2" "3"（傳遞了三個(gè)參數(shù)）

[test@localhost ~]$ cat var2_test.sh 
#!/bin/bash
echo "-------\$*----------"
for i in "$*"
do
    echo $i
done

echo "--------\$@---------"
for i in "$@"
do
    echo $i
done
[test@localhost ~]$ chmod +x var2_test.sh 
[test@localhost ~]$ ./var2_test.sh 1 2 3 4
-------$*----------
1 2 3 4
--------$@---------
1
2
3
4
[test@localhost ~]$

默認(rèn)參數(shù)（變量默認(rèn)值）

-變量為null
取默認(rèn)值

• 變量為null時(shí)贴浙，輸出默認(rèn)值
  ${var-defaultval}

[test@localhost ~]$ unset var
[test@localhost ~]$ echo ${var}

[test@localhost ~]$ echo ${var-test}
test
[test@localhost ~]$ echo ${var}

[test@localhost ~]$ var=""
[test@localhost ~]$ echo ${var-test}

[test@localhost ~]$ echo ${var}

[test@localhost ~]$

=變量為null時(shí)，同時(shí)改變變量值

[test@localhost ~]$ unset var1
[test@localhost ~]$ echo ${var1}

[test@localhost ~]$ echo ${var1=test}
test
[test@localhost ~]$ echo ${var1}
test
[test@localhost ~]$ var1=""
[test@localhost ~]$ echo ${var1}

[test@localhost ~]$ echo ${var1=test}

[test@localhost ~]$ echo ${var1}

[test@localhost ~]$ 

:-變量為null或空字符串署恍，取默認(rèn)值
${var:-defaultval}

[test@localhost ~]$ unset var2
[test@localhost ~]$ echo ${var2}

[test@localhost ~]$ echo ${var2:-test}    #驗(yàn)證變量為null
test
[test@localhost ~]$ echo ${var2}

[test@localhost ~]$ var2=""
[test@localhost ~]$ echo ${var2}

[test@localhost ~]$ echo ${var2:-test}    #驗(yàn)證變量為空字符串
test
[test@localhost ~]$ echo ${var2}

[test@localhost ~]$

:=變量為null或空字符串崎溃，同時(shí)改變變量值
${var:=defaultval}

[test@localhost ~]$ unset var3
[test@localhost ~]$ echo ${var3}

[test@localhost ~]$ echo ${var3:=test}   #驗(yàn)證變量為null
test
[test@localhost ~]$ echo ${var3}
test
[test@localhost ~]$ var3=""
[test@localhost ~]$ echo ${var3}

[test@localhost ~]$ echo ${var3:=test}   #驗(yàn)證變量為空字符串
test
[test@localhost ~]$ echo ${var3}
test
[test@localhost ~]$ 

:?變量為null或空字符串報(bào)錯(cuò)并退出

[test@localhost ~]$ unset var4
[test@localhost ~]$ echo ${var4}

[test@localhost ~]$ echo ${var4:?error}
-bash: var4: error
[test@localhost ~]$ echo ${var4}

[test@localhost ~]$ var4=""
[test@localhost ~]$ echo ${var4}

[test@localhost ~]$ echo ${var4:?error}
-bash: var4: error
[test@localhost ~]$ echo ${var4}

[test@localhost ~]$ 

:+變量不為空時(shí)使用默認(rèn)值
與:-相反

[test@localhost ~]$ var5="test"
[test@localhost ~]$ echo ${var5:+defaultest}
defaultest
[test@localhost ~]$ echo ${var5}
test
[test@localhost ~]$

參考文獻(xiàn)：https://www.linuxidc.com/Linux/2018-11/155618.htm

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