Shell programming: For Loop

Hell Programming--for in loop

-------in format-------

1. For no $ variable in string
2. Do
3. $ variable
4. Done

A simple string to enumerate through the calendar, with the function of using the in format to cut the string by a space

1. services="8000 3306"
3. For x in $SERVICES
4. Do
5. Iptables-a input-p TCP--dport $x-M state--state New-j ACCEPT
6. Done

-------for variable in values--------------string array to assign values sequentially

1. #!/bin/sh
2. For i in a B C string list A B C
3. The string is separated by a space, without parentheses, without commas, and then looping to assign it to the variable i
4. Variable does not have $
5. Do
6. echo "I is $i"
7. Done

[[Email protected] ~]$ sh Test.shi is an AI is bi is a C-------for in, variables and * are not equivalent-------

1. #!/bin/bash
2. For i in *.h;
3. Do
4. Cat ${i}.h
5. Done

[Email protected] test]$./TIP.SHCAT: *.h.h:no such file or directory $i represents the entire path, not the *.h. h part of the previous correction

1. #!/bin/bash
2. For I in *.h
3. Do
4. Cat $i
5. Done

[Email protected] test]$ echo hahaha >>1.h[[email protected] test]$ echo ha >>2.h [[email protected] test]$. /tip.shhahahaha Example 2:

1. For I in/etc/profile.d/*.sh
2. Do
3. $i
4. Done

$i represents/etc/profile.d/color.sh,/etc/profile.d/alias.sh,/etc/profile.d/default.sh-------for-in pair (command line, function) parameter traversal----- --

1. test ()  
2. { 
3.          local i 
4.         for i  in $* ; do 
5.               echo  "i is  $i"  
6.          done 
7. } 

$* is a string: with "parameter 1 parameter 2 ... "The form holds all parameters $i is the application of the variable i represents [[email protected] ~]$ sh test.sh p1 p2 p3 P4 I am p1i is P2i are P3i is a P4-------for in statement with wildcard * , Batch processing file-------batch change file name [[email protected] testtip]# lsaaa.txt ccc.txt eee.txt ggg.txt hhh.txt jjj.txt lll.txt nnn. Txtbbb.txt ddd.txt fff.txt go.sh iii.txt kkk.txt mmm.txt ooo.txt[[email protected] testtip]# cat go.sh

1. For I in *.txt *.txt is equivalent to an array of strings, looping to I in turn
2. Do
3. MV "$i" "$i. Bak"
4. Done

[[Email protected] testtip]# sh go.sh [[email protected] testtip]# Lsaaa.txt.bak ccc.txt.bak eee.txt.bak ggg.txt.bak H Hh.txt.bak jjj.txt.bak lll.txt.bak nnn.txt.bak bbb.txt.bak ddd.txt.bak fff.txt.bak go.sh iii.txt.bak kkk.txt . bak Mmm.txt.bak Ooo.txt.bak-------for the in statement with "' and $ (), using the" or $ () of a line of multiple lines of defects, is actually a string array-------

1. For I in $ (LS *.txt)
2. Do
3. Echo $i
4. Done

[[Email protected] ~]$ sh test111-tmp.txt111.txt22.txt33.txt or, using for in to overcome the multiple lines of "and $ () a line of defects-------take advantage of the for-in automatic string traversal by space Features, traversal of multiple directories-------

1. list="rootfs usr data data2"
3. For d in $LIST; Do
4. mount/backup/$d
5. Rsync-ax--exclude fstab--delete/$d//backup/$d/
6. umount/backup/$d
7. Done

Linux Shell for loop notation summary ********

1. For ((i=1;i<=10;i++));d o echo $ (expr $i \* 4);d One
2. Common in shell is for I in $ (seq 10)
3. For i in ' ls '
4. For i in ${arr[@]}
5. For i in $*; Do
6. For File in/proc/sys/net/ipv4/conf/*/accept_redirects; Do
7. For I in F1 F2 F3;d o
8. For I in *.txt
9. For I in $ (LS *.txt)

The for-in statement is used in combination with "' and $ (), and the defect that uses the" or $ () to line up a row is actually a string array ============-_-==============for num in $ (SEQ 1 100)

1. list="rootfs usr data data2"
2. For d in $LIST; Do
3. Use the for in statement to automatically traverse the character string by space, traversing multiple directories
4. For i in {1..10}
5. For I in Stringchar {1..10}
6. awk ' Begin{for (i=1; I<=10; i++) Print i} '

Note: The For loop notation in awk is the same as the C language ===============================================================

2. #/bin/bash
4. # Author: Zhou Haihan
6. # date:2010.3.25
8. # Blog.csdn.net/ablo_zhou
12. Arr= ("A" "B" "C")
14. echo "Arr is (${arr[@]})"
16. echo "Item in array:"
18. For i in ${arr[@]}
20. Do
22. echo "$i"
24. Done
26. echo "parameter, \$* represents all parameters entered by the script:"
28. For i in $*; Do
30. Echo $i
32. Done
34. Echo
36. echo ' Processing file/proc/sys/net/ipv4/conf/*/accept_redirects: '
38. For File in/proc/sys/net/ipv4/conf/*/accept_redirects; Do
40. Echo $File
42. Done
44. echo "Specify looping content directly"
46. For I in F1 F2 F3;d o
48. Echo $i
50. Done
52. Echo
54. echo "C syntax for loop:"
56. For (( i=0; I<i++);
58. Echo $i
60. Done

---------------------------------------------------------------------------------------------------------shell for loop usage sh ell syntax good trouble, a loop has been a while, found a few different ways to achieve output 1-100 can be divisible by 3 of the number 1. (())

1. #!/bin/bash
2. Clear
3. For ((i=1;i<100;i++ )
4. For
5. Do
6. if ((i%3==0))
7. Then
8. Echo $i
9. Continue
10. Fi
11. Done

2. Use ' SEQ 100 '

1. #!/bin/bash
2. Clear
4. For i in ' SEQ 100 '
5. Do
6. if ((i%3==0))
7. Then
8. Echo $i
9. Continue
10. Fi
11. Done

3. Using the While

1. #!/bin/bash
2. Clear
4. i=1
5. while (($i<))
6. Do
7. if (($i%3==0))
8. Then
9. Echo $i
10. Fi
11. i=$ (($i + 1))
12. Done

--------------------------------------------------------------------------------------------------------the shell uses the for loop to increment the number. , there are several ways to list the shell for loop: 1.

1. For i in ' seq 1 1000000 ';d o
3. Echo $i
5. Done

With seq 1 10000000 increment, before using this method did not encounter problems, because the previous I was useless to million (1000000), because the project needs me this number is far greater than million, found that the SEQ value to 1000000 when converted to 1e+06, Can not be used as the number of other operations, or the $i valid, correct access, and then seek other methods to solve, as follows 2.

1. For ((i=1;i<10000000;i++);d o
3. Echo $i
5. Done

3.

1. i=1
3. while ($i<10000000);d o
5. Echo $i
7. i= ' expr $i + 1 '
9. Done

Because this method calls expr so the speed will be slower than the 1th, 2nd, but can be slightly improved, the i= ' expr $i + 1 ' to i=$ (($i + 1)) can be slightly increased speed, but depends on the corresponding shell environment support 4.

1. For I in {1..10000000;do
3. Echo $i
5. Done

In fact, the choice of which method specific or to be supported by the corresponding shell environment, to achieve the desired results, and then consider the problem of speed. [Email protected] mnt]# ll-rw-r--r--1 root root 0 Mar 14:24 test.20130326-rw-r--r--1 root root 0 Mar 2 8 14:24 test.20130327-rw-r--r--1 root root 0 Mar 14:24 test.20130328-rw-r--r--1 root root 0 Mar 28 14:2 4 test.20130329

1. #!/bin/bash
2. d= ' Date +%y%m%d '
3. For A in ' ls | grep $D '
4. Do
5. echo "$A"

[Email protected] mnt]#/aa.sh Test.20130328done

Shell programming: For Loop