Bash Check if string contains only numeric

To check if string contains only numeric digits in Bash scripting, you can use regular expression ^[0-9]+$. In this expression ^ matches starting of the string, [0-9]+ matches one or more digits, and $ matches end of the string.

Examples

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

example.sh

#!/bin/bash
 
str="123454321"

if [[ $str =~ ^[0-9]+$ ]]; then
  echo "String contains only numeric digits."
else
  echo "String does not contain only numeric digits."
fi

Output

sh-3.2# ./example.sh 
String contains only numeric digits.

Now let us take a value in the string str such that it not only contains digits, but also some alphabets.

example.sh

#!/bin/bash
 
str="123454321ABC"

if [[ $str =~ ^[0-9]+$ ]]; then
  echo "String contains only numeric digits."
else
  echo "String does not contain only numeric digits."
fi

Output

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

References

Bash If Else

Conclusion

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