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The shell handles strings

Popularity：242 ℃/2025-04-08 16:34:02

concept

Strings are the most commonly used and useful data types in shell programming (except numbers and strings, there are no other types that are easy to use). Strings can be in single quotes, double quotes, or without quotes.

Single quotes declare string

  • Any character in single quotes will be output as it is, and variables in single quotes strings are invalid;
  • Single quotes cannot appear in single quotes (not after using escape characters for single quotes), but they can appear in pairs and be used as string splicing.

Double quotes declare string

  • There can be variables in double quotes
  • Escape characters can appear in double quotes

Example:

#The difference between single quotes and double quotes using variables
 root@master:~$ name='huangSir'
 root@master:~$ echo '$name'
 $name
 root@master:~$ echo "$name"
 huangSir

 #Nested single quotes in single quotes
 root@master:~$ echo ''hello world''
 hello world
 #Nested single quotes in double quotes
 root@master:~$ echo "'hello world'"
 'hello world'

 #The difference between single quotes and double quotes using escaped characters
 root@master:~$ echo '\"hello world\"'
 \"hello world\"
 root@master:~$ echo "\"hello world\""
 "hello world"

Various operations of strings

In Shell scripts, strings are common data types, and strings can be processed in many ways, including splicing, intercepting, substitution, comparison and other operations.

String stitching

String stitching can be directly spliced ​​without any special characters in the middle

root@master:~$ str1="hello"
root@master:~$ str2="world"
root@master:~$ str3="$str1 $str2"
root@master:~$ echo $str3
hello world
root@master:~$ str3="${str1} like  ${str2}"
root@master:~$ echo $str3
hello like world

Get the string length${#str}

Statistics character length (how many characters are there in a variable)

#Spaces are also considered characters
 root@master:~$ str="I Like Shell"
 root@master:~$ echo ${#str}
 12

Intercept string${str:index:index} 

root@master:~$ str="hello world"
 # Start with the index subscript of 5, intercept backwards, discard the index subscript of 5
 root@master:~$ echo ${str:5}
 world
 # Start with the index subscript of 2 and intercept 5 characters backwards
 root@master:~$ echo ${str:2:5}
 llo w
 # Start with the index subscript of 2 and intercept the 6th character to the last
 root@master:~$ echo ${str:2:-6}
 llo
 Starting from the index subscript of 2, the 7th character to the end is intercepted
 root@master:~$ echo ${str:2:-7}
 ll

String replacement

${str/newStr/oldStr}
WillnewStrReplace witholdStr, only replace the first one encounteredoldStr

root@master:~$ str="hello world"
root@master:~$ echo ${str/l/o}
heolo world

${str//newStr/oldStr}
WillnewStrReplace witholdStr, replace alloldStr

root@master:~$ str="hello world"
root@master:~$ echo ${str//l/o}
heooo worod

String case conversion

Requires a version of bash4+

Caps conversion:${str^^}

root@master:~$ str="hello world"
root@master:~$ echo ${str^^}
HELLO WORLD

Lowercase conversion:${str,,}

root@master:~$ str="HELLO WORLD"
root@master:~$ echo ${str,,}
hello world

Split string into array

root@master:~$ str="apple:banana:orange"
 #According to:Split
 root@master:~$ IFS=':' read -ra arr <<< "$str"
 root@master:~$ echo ${arr[0]}
 apple
 root@master:~$ echo ${arr[1]}
 banana

Remove prefix or suffix

  • ${str#word}: Start deleting from the left side of the variable and delete according to the shortest match
  • ${str##word}: Start deleting from the left side of the variable and delete according to the longest match
  • ${str%word}: Start deleting from the right side of the variable and delete according to the shortest match
  • ${str%%word}: Start deleting from the right side of the variable and delete according to the longest match
    Example:
root@master:~$ str=""
root@master:~$ echo ${str#*.}

root@master:~$ echo ${str##*.}
gz
root@master:~$ echo ${str%.*}

root@master:~$ echo ${str%%.*}
file

Determine whether substrings are included

if [[ $str == *World* ]]; then
   echo "Includes World"
 fi
 # or use regular expressions
 if [[ $str =~ .*World.* ]]; then
   echo "Match Successfully"
 fi

Determine whether the string is empty

[[ -z "$str" ]]: Return to true for empty
[[ -n "$str" ]]: Non-empty returns to true

root@master:~$ name=
root@master:~$ [[ -z "$name" ]] && echo true || echo false
true
root@master:~$ [[ -n "$name" ]] && echo true || echo false
false

Determine whether two strings are equal

[[ $str1 == $str2 ]]: Equal judgment
[[ $str1 != $str2 ]]: Unable to judge

root@master:~$ [[ "hello" == "hello" ]] && echo true || echo false
true
root@master:~$ [[ "hello" != "hello" ]] && echo true || echo false
false
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