How to check if a string contains a substring in Bash script programming

In this tutorial, the Bash script checks if the string contains a substring.

There are multiple ways to check if a string contains a substring.

Check substring exists in a string using the comparison operator

string variable is defined with text
using if statements, compare string with substring using comparison operator(==) and wildcard(*)
finally, print the string if the string contains

mainstring='Welcome to w3schools'
if [[ $mainstring == *"w3schools"* ]]; then
  echo "w3schools exists in main string"
fi

=~ operator used for searching substring for a given string.

used if block in a batch script.

Here is an example code

mainstring='Welcome to w3schools'
if [[ $mainstring =~ "w3schools" ]]; then
  echo "w3schools exists in main string"
fi

grep command searches for a given string and is piped to the main string to compare it.

mainstring='Welcome to w3schools'

if echo "$mainstring" | grep -q "w3schools"; then
  echo "w3schools exists in main string"
fi