Shell string variable

1 Introduce

character string （String） It is a combination of a series of characters . The string is Shell One of the most commonly used data types in programming （ Besides numbers and strings , There are no other types ）

2 Three formats of string

1 Single quotation mark method
2 Double quotation marks , recommend
3 No quotation marks

vim string.sh

#!/bin/bash
name1='james'
name2="kobe"
name3=paul

echo "name1: ${name1}"
echo "name2: ${name2}"
echo "name3: ${name3}"

3 The three formats of strings differ

1 Use single quotes ’' String
Any character will be output as it is , Using variables in concatenated strings is invalid .

2 By double quotation marks " " Surrounded string
It contains variables , Then the variable will be parsed to get the value , Instead of outputting it as it is .

3 A string that is not surrounded by quotation marks

Variables in strings that are not surrounded by quotation marks are also parsed , This point and double quotation marks " " The surrounding string is the same .
No spaces in the string , Otherwise, the string after the space will be parsed as other commands .

demo:

vim string.sh

#!/bin/bash
name="kobe"


echo ' Print with single quotation marks  name: ${name}'
echo " Use double quotation marks to print  name: ${name}"
echo   Do not use quotation marks for printing name:${
    name}

4 Get string length

4.1 grammar

${# String variable name }

4.2 meaning

Get string length

#!/bin/bash
name="kobe"


echo ' Print with single quotation marks  name: ${name}'
echo " Use double quotation marks to print  name: ${name}"
echo   Do not use quotation marks for printing name:${
    name}


echo " String length is : ${#name}"

4.3 result

5 String splicing

5.1 Splicing method

1 Unsigned splicing
2 Double quotation mark splicing

5.2 demo

#!/bin/bash
hello="hello"
world="world"
hello_world=${
    hello}${
    world}
echo " Unsigned splicing : ${hello_world}"

hello_world1="${hello}${world}"
echo " Double quotation mark splicing ：${hello_world}"

6 String interception

6.1 grammar

Format	explain
${ Variable name :start:length}	from string To the left of the string start Character start , Intercept to the right length Characters .start from 0 Start
${ Variable name :start}	from string To the left of the string start Characters begin to intercept , Until the last .
${ Variable name :0-start:length}	from string To the right of the string start Character start , Intercept to the right length Characters .start from 1 Start , Represents the first character on the right
${ Variable name :0-start}	from string To the right of the string start Characters begin to intercept , Until the last .
${ Variable name #*chars}	from string The first occurrence to the left of the string *chars The position begins , Intercept *chars All characters on the right .
${ Variable name ##*chars}	from string The last occurrence to the left of the string *chars The position begins , Intercept *chars All characters on the right .
${ Variable name %chars*}	from string The first occurrence to the right of the string chars* The position begins , Intercept chars* All the characters on the left .
${ Variable name %%chars*}	from string The last occurrence to the right of the string chars* The position begins , Intercept chars* All the characters on the left

6.2 demo

 character string "hello world"

 From the left 0 Start , Intercept to the left 2 Characters 
 From the left 5 Start , Intercept all characters to the left 
 From the right 5 Start , Intercept to the right 2 Characters 
 Intercept the first character on the left l All characters on the right 
 Intercept the last character on the left l All characters on the right 
 Intercept the first character on the right l All the characters on the left 
 Intercept the last character on the right l All the characters on the left 

#!/bin/bash
string="hello world"

echo " String is : ${string}"


str1="${string:0:2}"
echo " From the left 0 Start , Intercept to the left 2 Characters : ${str1}"

str2="${string:5}"
echo " From the left 5 Start , Intercept all characters to the left : ${str2}"

str3="${string:0-5:2}"
echo " From the right 5 Start , Intercept to the right 2 Characters : ${str3}"

str4="${string#*l}"
echo " Intercept the first character on the left l All characters on the right : ${str4}"

str5="${string##*l}"
echo " Intercept the last character on the left l All characters on the right : ${str5}"

str6="${string%l*}"
echo " Intercept the first character on the right l All the characters on the left : ${str6}"

str7="${string%%l*}"
echo " Intercept the last character on the right l All the characters on the left : ${str7}"