[Shell] Shell Learning notes for

There are a lot of uses for the For loop in the shell, and I've been trying to summarize what I saw on the web today about the for loop usage.
Knot, feel very comprehensive, so turn around research and research, hey ...
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 $ (), with the flaw of" or $ () that would be a line of lines, actually combining a string
Array
============-_-==============for num in $ (SEQ 1 100)
10, list= "Rootfs usr data data2″
For d in $LIST; Do
Use the for in statement to automatically traverse the character string by space, traversing multiple directories
11, for I in {1..10}
12, for I in Stringchar {1..10}
13. awk ' Begin{for (i=1; i<=10; i++) Print i} '
Note: The For loop notation in awk is the same as the C language
===============================================================
01.#/bin/bash
02.# Author: Zhou Haihan
03.# date:2010.3.25
04.# Blog.csdn.net/ablo_zhou
05.arr= ("A" "B" "C")
06.echo "Arr is (${arr[@]})"
07.echo "item in array:"
08.for i in ${arr[@]}
09.do
echo "$i"
11.done
12.echo "parameter, \$* represents all parameters entered by the script:"
13.for i in $*; Do
14.echo $i
15.done
16.echo
17.echo ' processing file/proc/sys/net/ipv4/conf/*/accept_redirects: '
18.for File in/proc/sys/net/ipv4/conf/*/accept_redirects; Do
19.echo $File
20.done
21.echo "Specify circular content directly"
22.for i in F1 f2 F3;d o
23.echo $i
24.done
25.echo
26.echo "C syntax for loop:"
27.for ((i=0; i<10; i++)); Do
28.echo $i
29.done
———————————————————————————–
———————-
Shell in for loop usage
Shell syntax Good trouble, a loop to get a while, find a few different ways to achieve output 1-100 can be 3
The number of divisible
1. using (())
#!/bin/bash
Clear
For ((i=1;i<100;i++))
For
Do
if ((i%3==0))
Then
Echo $i
Continue
Fi
Done
2. Use ' SEQ 100 '
#!/bin/bash
Clear
For i in ' SEQ 100 '
Do
if ((i%3==0))
Then
Echo $i
Continue
Fi
Done
3. Using the While
#!/bin/bash
Clear
I=1
while (($i <100))
Do
if (($i%3==0))
Then
Echo $i
Fi
i=$ (($i + 1))
Done
———————————————————————————–
———————
When the shell uses the for loop to make the number increment, it finds a problem, and lists several methods for the shell for Loop:
1.
For i in ' seq 1 1000000 ';d o
Echo $i
Done
Increment with seq 1 10000000, before using this method did not encounter problems, because the previous I was useless to millions
(1000000) because the project needs me this number is far greater than million, found to convert the SEQ value to 1000000 when converted to 1e+06, the root
Can not be used as a number of other operations, or the $i effective, correct access, and then seek other methods to solve, as follows
2.
For ((i=1;i<10000000;i++));d o
Echo $i
Done
3.
I=1
while (($i <10000000));d o
Echo $i
i= ' expr $i + 1 '
Done
Because this method calls expr so the speed will be slower than the 1th, 2nd, but can be slightly improved, the i= ' expr $i + 1 ' change
For i=$ ($i + 1) It is possible to increase the speed slightly, but depends on whether the shell environment supports
4.
For I in {1..10000000;do
Echo $i
Done
In fact, the choice of which method specific or to be supported by the corresponding shell environment, to achieve the desired effect, and then consider the speed of
Problem.

[Shell] Shell Learning notes for