1.for 循环命令
domo1 从文本中读取，以空格隔开
#!/bin/bash
# basic for commond
for test in Alabama Ariaon Arkani Califorin
do
echo the text state is $test
done
//
hadoop@master:~/shell_test$ ./test1
the text state is Alabama
the text state is Ariaon
the text state is Arkani
the text state is Califorin
**如果遇到单引号，会把单引号之间的值作为一个单词，因此或者
转义，或者用双引号把有单引号的单词括起来**
demo2
从变量中读取列表
#!/bin/bash
# get word form list
list="Abal fdfd bdfd sfdc ddddd"
list=$list" Connecticut"
for state in $list
do
echo "Have you ever visted $state"
done
//
hadoop@master:~/shell_test$ ./test2
Have you ever visted Abal
Have you ever visted fdfd
Have you ever visted bdfd
Have you ever visted sfdc
Have you ever visted ddddd
Have you ever visted Connecticut
注意：等号左右不能有空格
demo3 从命令行读取值
#!/bin/bash
#read values form a file
file="test1"
for state in `cat $file`
do
echo "Visit beatuful $state"
done
//
hadoop@master:~/shell_test$ ./test3
Visit beatuful #!/bin/bash
Visit beatuful #
Visit beatuful basic
Visit beatuful for
Visit beatuful commond
Visit beatuful for
Visit beatuful test
Visit beatuful in
Visit beatuful Alabama
demo 4
更改变量分割符号
#!/bin/bash
#read values form a file
file="test1"
IFS=$'\n'
for state in `cat $file`
do
echo "Visit beatuful $state"
done
//
hadoop@master:~/shell_test$ ./test4
Visit beatuful #!/bin/bash
Visit beatuful # basic for commond
Visit beatuful for test in Alabama Ariaon Arkani Califorin
Visit beatuful do
Visit beatuful echo the text state is $test
Visit beatuful done
注意：
如果在一个地方用了默认值，其他地方再修改回来，可以这样设置
IFS.OLD=$IFS
IFS=$'\n'
//其他代码
IFS=$IFS.OLD
可以指定多个的
IFS=$'\n:;"'
demo5 用通配符读取目录
#!/bin/bash
#iterating from multiple directories
for file in /home/hadoop/*
do
if [ -d "$file" ]
then
echo "$file is a directory"
elif [ -f "$file" ]
then
echo "$file is a File"
else
echo "$file does'not exist"
fi
done
//
hadoop@master:~/shell_test$ pwd
/home/hadoop/shell_test
hadoop@master:~/shell_test$ vi test5
hadoop@master:~/shell_test$ ./test5
/home/hadoop/apache-flume-1.6.0-bin is a directory
/home/hadoop/apache-flume-1.6.0-bin.tar.gz is a File
/home/hadoop/apache-maven-3.3.3 is a directory
/home/hadoop/eclipse is a directory
/home/hadoop/file1 is a File
/home/hadoop/hadoop-2.7.1 is a directory
...
...
注意：
还可以合并多个for目录
for file in /home/hadoop/* /home/chenhang/*
C语言风格的for循环
#!/bin/bash
#multiple variable for c
for (( a=1, b=10; a <=10; a++,b-- ))
do
echo "$a - $b"
done
//hadoop@master:~/shell_test$ ./test6
1 - 10
2 - 9
3 - 8
4 - 7
5 - 6
6 - 5
7 - 4
8 - 3
9 - 2
10 - 1
2.while 循环 util 命令和while命令相反
#!/bin/bash
#while demo test
var1=10
while echo $var1
[ $var1 -ge 0 ]
do
echo "this is inside the loop"
var1=$[ $var1 -1 ]
done
//
hadoop@master:~/shell_test/while$ ./test1
10
this is inside the loop
9
this is inside the loop
8
this is inside the loop
7
this is inside the loop
6
this is inside the loop
5
this is inside the loop
4
this is inside the loop
3
this is inside the loop
2
this is inside the loop
1
this is inside the loop
0
this is inside the loop
-1
demo2
循环嵌套处理文件数据例子
#!/bin/bash
# circle change fiel content
IFS.OLD=$IFS
IFS=$'\n'
for entry in `cat /etc/passwd`
do
echo "values in $entry"
IFS=:
for value in $entry
do
echo " $value"
done
done
//
hadoop@master:~/shell_test/while$ ./test2
./test2: 行 4: IFS.OLD=: 未找到命令
values in root:x:0:0:root:/root:/bin/bash
root
x
0
0
root
/root
/bin/bash
values in daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
daemon
x
1
1
daemon
/usr/sbin
/usr/sbin/nologin
demo3
控制循环语句 break 和continue
break 2 是跳出2层，默认为1
#!/bin/bash
#skip outer loop
for (( a = 1; a<4; a++ ))
do
echo "OUter loop : $a"
for (( b= 1; b <100; b++))
do
if [ $b -gt 4 ]
then
break 2
fi
echo " INner loop $b"
done
done
//
hadoop@master:~/shell_test/while$ ./test3
OUter loop : 1
INner loop 1
INner loop 2
INner loop 3
INner loop 4
demo 4
处理for循环的输出，重定向到文件或者程序
#!/bin/bash
#piping a loop to another file
for (( a = 1; a<10 ; a++ ))
do
echo "number is $a"
done > text.txt
echo "the commond is finished"
//hadoop@master:~/shell_test/while$ cat text.txt
number is 1
number is 2
number is 3
number is 4
number is 5
number is 6
number is 7
number is 8
number is 9
重定向到程序
#!/bin/bash
#piping a loop to annoter command
for state in "northr annia" Connjre jfdl9 Alabama Tennes
do
echo "$state is the next palce to go "
done | sort
echo "this completes our travels"
//
hadoop@master:~/shell_test/while$ ./test5
Alabama is the next palce to go
Connjre is the next palce to go
jfdl9 is the next palce to go
northr annia is the next palce to go
Tennes is the next palce to go
this completes our travels
跟新
1.遍历多个值，可以set -- $planet 分割
#!/bin/bash
echo "$@"
for planet in "mercury 36" "venus 67"
do
set -- $planet
echo "$1 $2,000,000 miles form sun"
done
exit 0
一个遍历文件的demo
#!/bin/bash
# fileinfo.sh
FILES="/usr/sbin/accept
/usr/sbin/pwck
/usr/sbin/chroot
/usr/bin/fakefile
/sbin/badblocks
/sbin/ypbind" # List of files you are curious about.
# Threw in a dummy file, /usr/bin/fakefile.
echo
for file in $FILES
do
if [ ! -e "$file" ] # Check if file exists.
then
echo "$file does not exist."; echo
continue # On to next.
fi
ls -l $file | awk '{ print $8 " file size: " $5 }' # Print 2 fields.
whatis `basename $file` # File info.
# Note that the whatis database needs to have been set up for this to work.
# To do this, as root run /usr/bin/makewhatis.
echo
done
exit 0
当遍历文件时候可以用？和*
#!/bin/bash
filename="*txt"
for file in $filename
do
echo "Contents of $file"
echo "---"
cat "$file"
echo
done
没有in的for 默认 $@
#!/bin/bash
for a
do
echo -n "$a "
done
# The 'in list' missing, therefore the loop operates on '$@'
#+ (command-line argument list, including whitespace).
echo
exit 0
列出系统的用户名字
#!/bin/bash
#userlist.sh
PASSWORD_FILE=/etc/passwd
n=1 # User number
for name in $(awk 'BEGIN{FS=":"}{print $1}' < "$PASSWORD_FILE" )
# Field separator = : ^^^^^^
# Print first field ^^^^^^^^
# Get input from password file /etc/passwd ^^^^^^^^^^^^^^^^^
do
echo "USER #$n = $name"
let "n += 1"
done
# USER #1 = root
# USER #2 = bin
# USER #3 = daemon
# ...
# USER #33 = bozo
