string


Remove all non digit characters from String

The following Java snippet removes all non-digit characters from a String.
Non-digit characters are any characters that are not in the following set [0, 1, 2, 3, 4 ,5 ,6 ,7 ,8, 9].

myString.replaceAll("\\D", "");

For a summary of regular-expression constructs and information on the character classes supported by Java pattern visit the following link.

The \\D pattern that we used in our code is a predefined character class for non-digit characters. It is equivalent to [^0-9]that negates the predefined character class for digit characters [0-9].


Java: remove leading character (or any prefix) from String only if it matches

The following snippet allows you to check if a String in Java starts with a specific character (or a specific prefix) that you are looking for and remove it.
To keep the number of lines small, we used the Java ?: ternary operator, which defines a conditional expression in a compact way.
Then, to quickly check if the first character(s) is the one we are looking for before removing it we used the String.startsWith().
To compute the number of characters to remove we used the String.length() on the needle.
Finally, to strip the leading character(s) we used String.substring() whenever the prefix matched.

final String needle = "//";
final int needleSize = needle.length();
String haystack = "";
haystack = haystack.startsWith(needle) ? haystack.substring(needleSize) : haystack;
System.out.print(haystack);

haystack = "apple";
haystack = haystack.startsWith(needle) ? haystack.substring(needleSize) : haystack;
System.out.println(haystack);

haystack = "//banana";
haystack = haystack.startsWith(needle) ? haystack.substring(needleSize) : haystack;
System.out.println(haystack);

The above code will result in the following:

apple
banana

 

Bonus: to remove all the instances of a character anywhere in a string:

final String needle = "a";
final int needleSize = needle.length();
String haystack = "banana";
haystack = haystack.replace(needle,"");
System.out.println(haystack);

The above code will result in the following:

bnn

Bonus: to remove the first instance of a character anywhere in a string:

final String needle = "a";
final int needleSize = needle.length();
String haystack = "banana";
haystack = haystack.replaceFirst(needle,"");
System.out.println(haystack);

The above code will result in the following:

bnana

JavaSript: Remove all non printable and all non ASCII characters from text

According to the ASCII character encoding, there are 95 printable characters in total.
Those characters are in the range [0x20 to 0x7E] ([32 to 126] in decimal) and they represent letters, digits, punctuation marks, and a few miscellaneous symbols.
Character 0x20 (or 32 in decimal) is the space character ' ' and
character 0x7E (or 126 in decimal) is the tilde character '~'.
Source: https://en.wikipedia.org/wiki/ASCII#Printable_characters

Since all the printable characters of ASCII are conveniently in one continuous range, we used the following to filter all other characters out of our string in JavaScript.

printable_ASCII_only_string = input_string.replace(/[^ -~]+/g, "");

What the above code does is that it passes the input string through a regular expression which will match all characters out of the printable range and replace them with nothing (hence, delete them).
In case you do not like writing your regular expression with the space character to it, you can re-write the above regular expression using the hex values of the two characters as follows:

printable_ASCII_only_string = input_string.replace(/[^\x20-\x7E]+/g, "");


How to: remove prefix and suffix from a variable in bash 1

string="/scripts/log/mount_hello_kitty.log";
prefix="/scripts/log/mount_";
string=${string#$prefix}; #Remove prefix
suffix=".log";
string=${string%$suffix}; #Remove suffix
echo $string; #Prints "hello_kitty"

In the above example we have as input the variable string that contains following /scripts/log/mount_hello_kitty.log.

We want to remove from that variable the prefix, which is /scripts/log/mount_ and the suffix, which is .log.

The above code will replace in place the input that is contained in the variable string and remove the prefix and suffix we defined in the respective variables.

string=${string#$prefix} returns a copy of string after the prefix was removed from the beginning of the variable.

string=${string%$suffix} returns a copy of string after the suffix was removed from the end of the variable.


Remove the last character from a bash variable

The following method, removes the last character from a bash variable by using a regular expression that matches any character.

VAR=${VAR%?};

The functionality ${string%substring} deletes shortest match of $substring from the back of $string.
The question mark ? matches zero or one of the previous regular expression. It is generally used for matching single characters.
So by using ? as our $substring we instruct bash to match any character at the end of the variable and remove it.

Example

$ VAR="Banana";
$ VAR=${VAR%?};
$ echo $VAR;
Banan


Remove the first character from a bash variable

The following method, removes the first character from a bash variable by using a regular expression that matches any character.

VAR=${VAR#?};

The functionality ${string#substring} deletes shortest match of $substring from the front of $string.
The question mark ? matches zero or one of the previous regular expression. It is generally used for matching single characters.
So by using ? as our $substring we instruct bash to match any character at the beginning of the variable and remove it.

Example

$ VAR="Banana";
$ VAR=${VAR#?};
$ echo $VAR;
anana