Valid Phone Numbers

EASY

Description

Given a text file file.txt that contains a list of phone numbers (one per line), write a one-liner bash script to print all valid phone numbers.

You may assume that a valid phone number must appear in one of the following two formats: (xxx) xxx-xxxx or xxx-xxx-xxxx. (x means a digit)

You may also assume each line in the text file must not contain leading or trailing white spaces.

Example:

Assume that file.txt has the following content:

987-123-4567
123 456 7890
(123) 456-7890

Your script should output the following valid phone numbers:

987-123-4567
(123) 456-7890

Approaches

Checkout 4 different approaches to solve Valid Phone Numbers. Click on different approaches to view the approach and algorithm in detail.

Pure Bash `while` loop

This approach uses a while loop in bash to read the file line by line. For each line, it uses the [[ ... =~ ... ]] conditional expression to test if the line matches the required regular expression for a valid phone number. If it matches, the line is printed to standard output.

Algorithm

1. Start a while loop to read file.txt line by line into a variable line.
1. For each line, use the [[ ... =~ ... ]] operator to perform a regex match.
1. The regex checks for two patterns separated by | (OR): $[0-9]{3}$ [0-9]{3}-[0-9]{4} or [0-9]{3}-[0-9]{3}-[0-9]{4}.
1. The entire pattern is anchored with ^ and $ to ensure the whole line matches.
1. If the line matches the regex, print the line.
1. Continue until all lines are processed.

The script reads file.txt line by line using while read -r line. The -r option prevents backslash interpretation. Inside the loop, an if statement checks the line against a regular expression. The regex ^($[0-9]{3}$ [0-9]{3}-[0-9]{4}|[0-9]{3}-[0-9]{3}-[0-9]{4})$ is used to validate the two possible phone number formats. The ^ and $ anchors ensure that the entire line must match one of the formats. If the condition is true, echo "$line" prints the valid phone number. This can be written as a one-liner using the && operator.

while read -r line; do [[ "$line" =~ ^(\([0-9]{3}\) [0-9]{3}-[0-9]{4}|[0-9]{3}-[0-9]{3}-[0-9]{4})$ ]] && echo "$line"; done < file.txt

Complexity Analysis

Time Complexity: O(N * L)Space Complexity: O(L)

Pros and Cons

Pros:

No external utilities are needed; it's a pure bash solution.

Cons:

Significantly slower than using dedicated text-processing tools like grep, sed, or awk, especially for large files.
The one-liner syntax can be less readable.

Video Solution

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