A tutorial on the operation of Shell script arrays in Linux

Array Assignment: A= (1 2 3 4 5)
A[1]=1

Array length: Echo ${#a [@]}

or echo ${#a [*]}

Read array: Echo ${a[@]}

or Echo ${a[*]}
echo ${a[0]} PS: array subscript starting from 0
Delete array: unset a
Unset A[1]
Array fragmentation: Echo ${a[@]:0:3} displayed as 1,2,3 PS: Intercept the first 3 array values display
Array replacement: Echo ${a[@]/3/100} displayed as 1,2,100,4,5
Array Loop value usage:
For FILE in ${a[@]};d o
Echo ${file};
Done

Display values:

#!/bin/bash
chars= ' ABCDEFGHIJKLMNOPQRSTUVWXYZ '
for ((i=0; i<26; i++)); Todo
array[$i]=${chars: $i: 1}
echo ${array[$i]}
Done

Example Supplements

1. Place a string in an array to get its length

#!/bin/bash
Str= "A B--n D"
Array= ($STR)
length=${#array [@]}
Echo $length

for ((i=0; i< $length; i++))
Todo
echo ${array[$i]}
Done

Execution results:

[Oracle@99bill-as9 array]$ SH length.sh
4
A
B
--n
D

To print a string:

#!/bin/bash
Str= "a b C"
For I in $str
Todo
Echo $i
Done

Or:

#!/bin/bash
Str= "a b C"
Array= ($STR)
For ((i=0;i<${#array [@]};i++))
Todo
echo ${array[$i]}
Done

Execution results:

A
B
C

2. String is split with other characters

#!/bin/bash

Str2= "A#b#c"
A= ($ (echo $str 2 | tr ' # ' | tr-s '))
length=${#a [@]}

for ((i=0; i< $length; i++))
Todo
echo ${a[$i]}
Done
#echo ${a[2]}

Execution results:

A
B
C

3. Other actions for arrays

#!/bin/bash
Str= "A b--n dd"
Array= ($STR)
length=${#array [@]}

The first element of the array is the direct output of #ouput
Echo $array

#Use Subscript Way Access array accesses the elements of an element in a subscript way
Echo ${array[1]}

#Output the array output
Echo ${array[@]}

#Output in the array subscript for 3 the length of the element that is labeled 3 in the output array
Echo ${#array [3]}

#Output in the array subscript 1 to 3 element output array subscript 1 to 3
Echo ${array[@]:1:3}

#Output in the array subscript greater than 2 elements output array lower-than-2 element
Echo ${array[@]:2}

#Output in the array subscript less than 2 elements output array lower than 2 element
Echo ${array[@]::2}

Execution results:

A
B
A b--n DD
2
b--n DD
--n DD
A b

4. Traversal accesses a string (the default is separated by a space and can refer to 2 when the string is separated by another delimiter)

#!/bin/bash
Str= "a--m"
For I in $str
Todo
Echo $i
Done

Execution results:

A
--m

5. How to use Echo to output a string str= "-n". Because-n is an argument to echo, the general method of echo "$str" is not output.
Solutions can include:

echo X$str | Sed ' s/^x//'
Echo-ne "$STR \ n"
Echo-e "$str \n\c"
printf "%s\n" $str (this can also be)

1, from "standard input" read n times string, each input string stored in array

#!/bin/bash
I=0
N=5
While ["$i"-lt $n]; Todo
echo "Please input strings ... ' expr $i + 1 '"
Read array[$i]
b=${array[$i]}
echo "$b"
i= ' expr $i + 1 '
Done
2, put the letters in the string into the array, and output to the "standard output"

#!/bin/bash
chars= ' ABCDEFGHIJKLMNOPQRSTUVWXYZ '
for ((i=0; i<26; i++)); Todo
array[$i]=${chars: $i: 1}
echo ${array[$i]}
Done
What's interesting here is ${chars: $i: 1}, which means to get 1 characters starting from the $i position of the chars string. If you change 1 to 3, you get 3 characters ~ The result is:
Abc
Bcd
...
Vxy
Xyz
YZ//There is not enough string to get the
z//Not enough string to get the
Here are some examples of applying arrays to shell environment variables.

3. Apply the array to the shell environment variable (1)

Array Assignment:
[Root@pps ~]# season= ("srping" "Summer" "Autumn" "Winter")
When you find that the assignment is wrong, you can also immediately correct the new assignment, as Spring above is written as srping.
Re-assignment: (The original value is overridden)
[Root@pps ~]# season= ("Spring" "Summer" "Autumn" "Winter")

Check out the environment variables:
[Root@pps ~]# Set | grep SEASON
season= ([0]= "Spring" [1]= "Summer" [2]= "Autumn" [3]= "Winter")

Display the entire array:
[Root@pps ~]# echo ${season[*]} or echo ${season[@]}
Spring Summer Autumn Winter

To display an array element:
[Root@pps ~]# echo ${season[3]}
Winter

To assign a value to a single array element:
[Root@pps ~]# season[0]= "New_spring"

Look at the array again:
[Root@pps ~]# echo ${season[*]}
New_spring Summer Autumn Winter

Clears the specified single array element:
[Root@pps ~]# unset season[2]

Clear the entire array:
[Root@pps ~]# unset SEASON
4. Apply the array to the shell environment variable (2)
To convert a carriage return in a file to a space using the TR command:

[Root@pps ~]# Cat/etc/shells | TR "\ n" "" ">/tmp/tmp.file

To assign the contents of a file to an array: (before the first return character is encountered)

[Root@pps ~]# read-a SHELLS </tmp/tmp.file

To view array assignments:

[Root@pps ~]# Set | grep "SHELLS"
shells= ([0]= "/bin/sh" [1]= "/bin/bash" [2]=]/sbin/nologin [3]= "/bin/tcsh" [4]= "/bin/csh" [5]= "/bin/ksh"]

This array environment variable can be applied to other shell scripts or applications later.

Extraction of arrays
To start from the tail:

array= ([0]=one [1]=two [2]=three [3]=four]
${ARRAY[@]:1} # Two three four, remove all elements after the first element, then ${array[@]:0} represents all elements
${array[@]:0:2} # One Two
${array[@]:1:2} # Two Three
Sub-string deletion

[Root@localhost dev]# Echo ${array[@]:0}
One two three four
[Root@localhost dev]# Echo ${array[@] #t *e} # Start the shortest match on the left: ' T*e ', which will match to ' thre '
One two E four
[Root@localhost dev]# echo ${array[@]# #t *e} # Start the longest match on the left, which will match to ' three '
[Root@localhost dev]# array= ([0]=one [1]=two [2]=three [3]=four]]
[Root@localhost dev]# Echo ${array[@]%o} # Start the shortest match from the end of the string
One TW three Four
[Root@localhost dev]# Echo ${array[@]%%o} # start the longest match from the end of the string
One TW three Four
Child string Substitution

[Root@localhost dev]# array= ([0]=one [1]=two [2]=three [3]=four]]
The first one to be matched will be deleted.

[Root@localhost dev]# Echo ${array[@]/o/m}
Mne TWM Three Fmur
All matches will be deleted.

[Root@localhost dev]# Echo ${array[@]//o/m}
Mne TWM Three Fmur
No replacement substring is specified, then a matching substring is deleted

[Root@localhost dev]# Echo ${array[@]//o/}
NE tw three fur
Replacement string Front terminal string

[Root@localhost dev]# Echo ${array[@]/#o/k}
Kne two Three Four
Replacement string Rear terminal string

[Root@localhost dev]# Echo ${array[@]/%o/k}
One TWK three Four

All right, here we go. The array operation on the shell command is summed up here, hoping to help you.