控制流结构
1.if語句
if 條件1
then?
? ? ?命令1
elif 條件2
then?
? ? ?命令2
else
? ? ?命令3
fi
------------------
if 條件
then 命令
fi
eg：
#!/bin/bash
#if test
#this is a comment line
if [ "10" -lt "12" ];then
#yes 10 is less than 12
echo "yes,10 is less than 12"
else
echo "no"
fi
注意：if語句必須以fi終止
? ?"10" 前一個(gè)空格，“12”后也有一個(gè)空格。這個(gè)條件都是通過test命令來指定。條件表達(dá)為test expression或者[expression]
?
條件表達(dá)式中的比較函數(shù)
man test
NAME
? ? ? ?test - check file types andcompare values
SYNOPSIS
? ? ? ?test EXPRESSION
? ? ? ?[ EXPRESSION ]
? ? ? ?[ OPTION
DESCRIPTION
? ? ? ?Exit with the statusdetermined by EXPRESSION.
? ? ? ?--help display this help andexit
? ? ? ?--version
? ? ? ? ? ? ? outputversion information and exit
? ? ? ?EXPRESSION is true or falseand sets exit status. It is one of:
? ? ? ?( EXPRESSION )
? ? ? ? ? ? ?EXPRESSION is true
? ? ? ?! EXPRESSION
? ? ? ? ? ? ?EXPRESSION is false
? ? ? ?EXPRESSION1 -a EXPRESSION2
? ? ? ? ? ? ? bothEXPRESSION1 and EXPRESSION2 are true
? ? ? ?EXPRESSION1 -o EXPRESSION2
? ? ? ? ? ? ? eitherEXPRESSION1 or EXPRESSION2 is true
? ? ? ?[-n] STRING
? ? ? ? ? ? ? thelength of STRING is nonzero
? ? ? ?-z STRING
? ? ? ? ? ? ? thelength of STRING is zero
? ? ? ?STRING1 = STRING2
? ? ? ? ? ? ? thestrings are equal
? ? ? ?STRING1 != STRING2
? ? ? ? ? ? ??the strings are not equal
? ? ? ?INTEGER1 -eq INTEGER2
? ? ? ? ? ? ? INTEGER1is equal to INTEGER2
? ? ? ?INTEGER1 -ge INTEGER2
? ? ? ? ? ? ? INTEGER1is greater than or equal to INTEGER2
? ? ? ?INTEGER1 -gt INTEGER2
? ? ? ? ? ? ? INTEGER1is greater than INTEGER2
? ? ? ?INTEGER1 -le INTEGER2
? ? ? ? ? ? ? INTEGER1is less than or equal to INTEGER2
? ? ? ?INTEGER1 -lt INTEGER2
? ? ? ? ? ? ? INTEGER1is less than INTEGER2
? ? ? ?INTEGER1 -ne INTEGER2
? ? ? ? ? ? ? INTEGER1is not equal to INTEGER2
? ? ? ?FILE1 -ef FILE2
? ? ? ? ? ? ? FILE1and FILE2 have the same device and inode numbers
? ? ? ?FILE1 -nt FILE2
? ? ? ? ? ? ? FILE1 isnewer (modification date) than FILE2
? ? ? ?FILE1 -ot FILE2
? ? ? ? ? ? ? FILE1 isolder than FILE2
? ? ? ?-b FILE
? ? ? ? ? ? ? FILEexists and is block special
? ? ? ?-c FILE
? ? ? ? ? ? ? FILEexists and is character special
? ? ? ?-d FILE
? ? ? ? ? ? ? FILEexists and is a directory
? ? ? ?-e FILE
? ? ? ? ? ? ? FILEexists
? ? ? ?-f FILE
? ? ? ? ? ? ? FILEexists and is a regular file
? ? ? ?-g FILE
? ? ? ? ? ? ? FILEexists and is set-group-ID
? ? ? ?-h FILE
? ? ? ? ? ? ? FILEexists and is a symbolic link (same as -L)
? ? ? ?-G FILE
? ? ? ? ? ? ? FILEexists and is owned by the effective group ID
? ? ? ?-k FILE
? ? ? ? ? ? ? FILEexists and has its sticky bit set
? ? ? ?-L FILE
? ? ? ? ? ? ? FILEexists and is a symbolic link (same as -h)
? ? ? ?-O FILE
? ? ? ? ? ? ? FILEexists and is owned by the effective user ID
? ? ? ?-p FILE
? ? ? ? ? ? ? FILEexists and is a named pipe
? ? ? ?-r FILE
? ? ? ? ? ? ? FILEexists and is readable
? ? ? ?-s FILE
? ? ? ? ? ? ? FILEexists and has a size greater than zero
? ? ? ?-S FILE
? ? ? ? ? ? ? FILEexists and is a socket
? ? ? ?-t [FD]
? ? ? ? ? ? ? filedescriptor FD (stdout by default) is opened on a terminal
? ? ? ?-u FILE
? ? ? ? ? ? ? FILEexists and its set-user-ID bit is set
? ? ? ?-w FILE
? ? ? ? ? ? ? FILEexists and is writable
? ? ? ?-x FILE
? ? ? ? ? ? ?FILEexists and is executable
eg.
#!/bin/bash
#if test
#this is a comment line
echo "Enter your filename:"
read myfile
if [ -e $myfile ]
then
? ?if [ -s $myfile ];then
? ? echo "$myfile exist and size greaterthan zero"
? ?else
? ? echo "$myfile exist but size iszero"
? ?fi
else
echo "file no exist"
fi
[test@szbirdora 1]$ sh iftest.sh?
Enter your filename:
11
11 exist but size is zero
2.case語句
case語句為多選擇語句。
case 值 in
模式1）
? ? 命令1
? ? ;;
模式2)
? ? 命令2
? ? ;;
esac
eg.
#!/bin/bash
#case select
echo -n "enter a number from 1 to 3:"
read ans
case $ans in
1)
echo "you select 1"
;;
2)
echo "you select 2"
;;
3)
echo "you select 3"
;;
*)
echo "`basename $0`:this is not between 1 and3">2
exit;
;;
esac
3.for 循環(huán)
for循環(huán)一般格式：
for 變量名 in 列表 (列表以空格作為分割)
do
? ?命令1
? ?命令2
done
eg：
#!/bin/bash
#forlist1
for loop in 1 2 3 4 5
do
echo $loop
done
4.until循環(huán)
until 條件
do
? ?命令1
? ?命令2
? ?...
done
條件測試發(fā)生在循環(huán)末尾，所以循環(huán)至少可以執(zhí)行一次。
5.
while循環(huán)
while 命令 （可以是一個(gè)命令也可以是多個(gè)，做條件測試）
do
? ? ? 命令1
? ? ? 命令2
? ? ? ...
done
注意：如果從文件中讀入變量<filename要放到done后
6.break和continue控制
break跳出，continue跳過
總結(jié)
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