Bash Remove Special Characters from String

Using Parameter Expansion

Use the parameter expansion with regex to remove the special characters from a string in Bash.

In this example, the parameter expansion removes all special characters from the "Hello World! This is a test string." string. We can observe that our input string contained two special characters, the exclamation marks ! and the space character removed in the modified string.

Here’s a breakdown of the ${string//[^[:alnum:]]/""} expression:

• string is the input string we want want to modify.
• // is a pattern substitution operator that replaces all occurrences of a [^[:alnum:]] pattern with an empty string.
• [^[:alnum:]] is a regular expression pattern that matches any character that is not alphanumeric. The ^ symbol inside the square brackets means not, so this pattern matches any character, not in the [:alnum:] character class. The [:alnum:] character class represents all alphanumeric characters (letters and digits).
• "" is an empty string used as the replacement string.

Using sed Command

Use the sed command to remove the special characters from a string in Bash.

This example used the sed command to replace all non-alphanumeric characters with an empty string. The substitution operation(s) is used to replace the pattern [^[:alnum:]] with an empty string. Here, the // indicates that we want to replace the pattern with an empty string globally, and g is a flag that tells sed to perform the substitution operation on all matches in the input string, not just the first match.

Using tr Command

Use the tr command to remove the special characters from a string in Bash.

In the above example, the tr command deleted all characters not alphanumeric from the "My email is [email protected]" string. In other words, it is used to remove all special characters. Here, in the-dc parameter, d means delete and c means character. This -dc parameter tells the tr command to delete all characters that do not match the specified character set [:alnum:] (which matches all alphanumeric characters).

Using awk Command

Use the awk command to remove the special characters from a string in Bash.

In this bash example, the awk command removes the special characters from the "The phone number of the company is :(555) 555-1234" string and replaces all non-alphanumeric characters with an empty string. Here, the gsub function of the awk command is used to replace the pattern [^[:alnum:]] with an empty string "", and 1 is used to print the modified string.

Using grep Command

Use the grep command to remove the special characters from a string in Bash.

The grep command is used in the above example to match all alphanumeric characters in the string. The -o parameter outputs only the matching pattern, and the -E option enables extended regular expressions.

Here, the tr command removes any newline characters from the output of $new_string, effectively printing the output in a single line.

That’s all about bash remove special characters from String.