Bash – Check if string contains only alphanumeric

To check if string contains only alphanumeric in Bash scripting, you can use regular expression ^[a-zA-Z0-9]+$. In this expression ^ matches starting of the string, [a-zA-Z0-9]+ matches one or more lowercase or uppercase alphabets or numeric digits, and $ matches end of the string.

Examples

In the following script, we take a string in str which contains only alphanumeric characters. We shall programmatically check if string str contains only alphanumeric characters using regular expression.

example.sh

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#!/bin/bash
 
str="Apple123"

if [[ $str =~ ^[a-zA-Z0-9]+$ ]]; then
  echo "String contains only alphanumeric."
else
  echo "String does not contain only alphanumeric."
fi

Output

sh-3.2# ./example.sh 
String contains only alphanumeric.

Now let us take a value in the string str such that it not only contains alphanumeric characters, but also some spaces and special characters.

example.sh

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#!/bin/bash
 
str="Apple@12 3"

if [[ $str =~ ^[a-zA-Z0-9]+$ ]]; then
  echo "String contains only alphanumeric."
else
  echo "String does not contain only alphanumeric."
fi

Output

sh-3.2# ./example.sh 
String does not contain only alphanumeric.

References

Bash If Else

Conclusion

In this Bash Tutorial, we learned how to check if string contains only alphanumeric characters using regular expression.