1.if语句
if 条件1
then
命令1
elif 条件2
then
命令2
else
命令3
fi
------------------
if 条件
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语句必须以fi终止
"10" 前一个空格，“12”后也有一个空格。这个条件都是通过test命令来指定。条件表达为test expression或者[expression]
条件表达式中的比较函数
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语句
case语句为多选择语句。
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 循环
for循环一般格式：
for 变量名 in 列表 (列表以空格作为分割)
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循环
until 条件
do
命令1
命令2
...
done
条件测试发生在循环末尾，所以循环至少可以执行一次。
5.
while循环
while 命令 （可以是一个命令也可以是多个，做条件测试）
do
命令1
命令2
...
done
注意：如果从文件中读入变量<filename要放到done后
6.break和continue控制
break跳出，continue跳过
相关资源：linux shell 控制流结构