Linux shell Script Learning Note one

First, file comparison operators
-e filename true if filename exists [-e/var/log/syslog]
-D filename True if filename is a directory [-d/tmp/mydir]
-F filename True if filename is a regular file [-f/usr/bin/grep]
-L filename True if filename is a symbolic link [-l/usr/bin/grep]
-R filename True if filename is readable [-r/var/log/syslog]
-W filename if filename is writable, true [-w/var/mytmp.txt]
-X filename is true if filename is executable [-l/usr/bin/grep]
Filename1-nt filename2 If filename1 is newer than filename2, then true [/tmp/install/etc/services-nt/etc/services]
Filename1-ot filename2 If filename1 is older than filename2, then true [/boot/bzimage-ot Arch/i386/boot/bzimage]
String comparison operators (note the use of quotation marks, which is a good way to prevent whitespace from disturbing the code)
-Z String True if string length is zero [-Z ' $myvar ']
-N String if string length is nonzero, true [-n ' $myvar ']
string1= string2 If string1 is the same as string2, then true ["$myvar" = "One of the three"]
string1!= string2 If string1 differs from string2, true ["$myvar"! = "one, three"]
Arithmetic comparison operators
Num1-eq num2 equals [3-eq $mynum]
Num1-ne num2 Not equal to [3-ne $mynum]
Num1-lt num2 less than [3-lt $mynum]
Num1-le num2 less than or equal to [3-le $mynum]
NUM1-GT num2 greater than [3-GT $mynum]
Num1-ge num2 greater than or equal to [3-ge $mynum]

second, the use of arrays
1.How do I declare an array variable?
array[0]= "Zero" array[1]= "one" array[2]= "one"
OR
Declare-a Array
OR
Array= (Zero one)
OR
Array= "Zero One"
OR
array= ([0]= "Zero" [1]= "one" [2]= ")

2. How do I traverse an array? For ((i=0;i<${#array [@]};i++)] do echo ${array[i]}; Done OR for I in ${array[@]};d o echo $i;d one; 3.

Gets the length of the array

echo ${#array [@]} OR echo ${#array [*]}

4. Deleting an array element

Unset Array[0]

5. Deleting an array

unset array

6. Tiles like Python

Echo ${array[@]:0:2}

Echo ${array[@]:2}

Third, Linux shell check process pid

#
# Check the PID of such program
#
Checkpid () {
If [-z] ' PS x | grep $ | Grep-v grep | Grep-v | awk ' {print '} ' "]; Then
echo "the program cant run well."
Fi
}

Brief description:

PS Reporting Program status.

PS x shows all the programs, not the terminal to distinguish.

The first parameter of the function, such as: Checkpid test, then: $ = test,$0 = Checkpid Test.

Grep finds the strings in the file that match the criteria.

PS x | grep displays the status of the program that contains the keyword ' $ '.

PS x | grep $ | Grep-v grep | Grep-v to remove the influence of its own command

awk ' {print '} ' extracts the packet and formats the display of the command execution

Such as:

PS x | grep Test | Grep-v grep | Grep-v "Checkpid test"

After execution appears as:

12040 pts/1 Ss 0:00 test

So

PS x | grep Test | Grep-v grep | Grep-v "Checkpid Test" | awk ' {print '} '

is displayed as:

12040

That is the PID of the process.

Linux shell Script Learning Note one