1.for 循環命令
domo1 從文本中讀取，以空格隔開
#!/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
**如果遇到單引號，會把單引號之間的值作為一個單詞，因此或者
轉義，或者用雙引號把有單引號的單詞括起來**
demo2
從變量中讀取列表
#!/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：等號左右不能有空格
demo3 從命令行讀取值
#!/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
更改變量分割符號
#!/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 $test
Visit beatuful done
注意：
如果在一個地方用了默認值，其他地方再修改回來，可以這樣設置
IFS.OLD=$IFS
IFS=$'\n'
//其他代碼
IFS=$IFS.OLD
可以指定多個的
IFS=$'\n:;"'
demo5 用通配符讀取目錄
#!/bin/bash
#iterating from multiple directories
for file in /home/hadoop/*
do
if [ -d "$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：
還可以合并多個for目錄
for file in /home/hadoop/* /home/chenhang/*
C語言風格的for循環
#!/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 循環 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
循環嵌套處理文件數據例子
#!/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
控制循環語句 break 和continue
break 2 是跳出2層，默認為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
處理for循環的輸出，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.遍歷多個值，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
一個遍歷文件的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
當遍歷文件時候可以用？和*
#!/bin/bash
filename="*txt"
for file in $filename
do
echo "Contents of $file"
echo "---"
cat "$file"
echo
done
沒有in的for 默認 $@
#!/bin/bash
for a
do
echo -n "$a "
done
# The 'in list' missing, therefore the loop operates on '$@'
#+ (command-line argument list, including whitespace).
echo
exit 0
列出系統的用戶名字
#!/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
