Part Three Shell Programming 3 (Shell Script 2)

7. If you judge some special usage
If [-Z $a] This indicates what happens when the value of variable A is empty
If Grep-q ' 123 ' 1.txt; Then what happens if the 1.txt contains a ' 123 ' row
if [!-e file]; Then what happens when the file doesn't exist?
if (($a <1)); Then ... Equivalent to if [$a-lt 1]; Then ... Symbols such as <,>,==,!=,>=,<= cannot be used in []

if [! $a-gt 0];then ... Represents no more than 0

If [-Z $n 1] is empty
If [-n $n 1] is not empty
if [!-Z $n 1]

8. Case judgment in the shell
Format: Case variable name in
value1)
Command
;;
value2)
Command
;;
*)
Commond
;;
Esac

Find more !
Vim case.sh
!#/bin/bash
n1= ' echo $ |sed ' s/[0-9]//g '
if [-Z $n 1]; Then
m=$[$1%2]
Case $m in
1)
echo "The number is odd"
;;
0)
echo "The number is even"
;;
*)
echo " is Other"
;;
Esac
Else
echo "The character you input not a number"
fi

SH case.sh 6 represents the first parameter

9. Loops in shell scripts
For loop syntax structure: The for variable name in condition; Do ... done
While loop syntax structure: while condition; Do ... done dead loop used: denotes
Break directly ends this layer loop (jumps out of the entire loop); Continue ignores the code under continue (jump out of this loop) and proceed directly to the next loop
Exit directly out of the shell

Sequence
SEQ 1 [Step] 10 default is 1
Seq 1 10
Seq 10-1 1
Seq 10-2 1
Seq 1 2 10

Seq-w 1 100 width same ============
001
002
...
100
===============
Vim for.sh
!#/bin/bash
For i in ' SEQ 1 10 '
Do
Echo $i
Done

==========
Vim for.sh
!#/bin/bash
For file in ' ls '
Do
Ls-ld $file
Done

=========
Vim for.sh
!#/bin/bash
Sum=0
For n in ' seq 1 100 '
Do
sum=$[$sum + $n]
Done
Echo $sum

==========while dead Loop
Vim while.sh
!#/bin/bash
n1=1 here can be any value
While [!-Z $n 1]
Do
read-p "Input a number:" N
n1= ' echo $n |sed ' s/[0-9]//g '
Done
echo "The number is $n."
===========
Vim break.sh
!#/bin/bash
For I in 1 2 3 4 5
Do
Echo $i
if [$i-eq 3]
Then
Break
fi
Echo $i
Done

functions in the shell
The function is to organize a piece of code into a small unit, and give the small unit a name, when the code is used to call the name of the small unit directly.
format: function F_name () {
Command
}
the function has to be on the front
You can export global variables in a function
===============
function MySum () {
Sum=$[$1+$2]
Echo $sum
}
s= ' mysum 1 2 '
Echo $s
===============
function MySum () {
Sum=$[$1+$2]
return $sum
}
mysum 1 2
echo $?
=============
function MySum () {
sum=$[$1+$2] If the sum is preceded by a local, it takes effect inside the function

}
MySum 1
Echo $sum
===========

One. Shell Exercises
Write a shell script that calculates the 1-100 and;
Write the shell script, ask to enter a number, and then calculate from 1 to the input number and, if the input number is less than 1, then re-enter until the correct number is entered;

vim sum.sh
!#/bin/bash
Span style= "font-size:15px;" >if_nu () {
n1= ' echo $1|sed ' s/[0-9]//g ' '
If [-Z $n 1]
then
if [$1-GT 1]; then return 1; else return 0;fi
else
return 0
fi
}

Read-p "Input a number:" N
If_nu $n
N2= ' echo $? '
If [$n 2-eq 1]
Then
Sum=0
For i in ' seq 1 $n '
Do
sum=$[$sum + $i]
Done
Echo $sum
Else
echo "The character you input is not number"
Fi

Write shell scripts to copy all directories under the/root/directory (only one level) to the/tmp/directory;
Find/root-maxdepth 1-type D Search the root of the first level directory
===========
For D in ' ls/root/'; do if [-D $d]; Then Cp-r $d/tmp/;fi; Done

For D in ' find/root-maxdepth 1-type d '; do if [-D $d]; Then Cp-r $d/tmp/;fi; Done

Write shell scripts, batch build user user_00, user_01, ... user_100 and all users belong to the Users group;

For i in ' seq-w 0 99 '; Do useradd-g users user_$i; Done

Write a shell script that intercepts the first column in the line containing the keyword ' abc ' in the file Test.log (assuming the delimiter is ":"), then sorts the intercepted numbers (assuming the first column is a number), and then prints out the columns with more than 10 repetitions;

Awk-f: '/abc/{print '} ' test.log |sort |uniq-c |sort-n |awk ' $1>10 '

Part Three Shell Programming 3 (Shell Script 2)