Tenth Line

Tenth Line - Problem

Shell Easy

Given a text file file.txt, write a shell command or script to print just the 10th line of the file.

Note: If the file has fewer than 10 lines, the output should be empty (nothing printed).

Input & Output

Example 1 — File with 15 lines

$ Input: file.txt contains 15 lines, line 10 is "tenth line content"

› Output: tenth line content

💡 Note: The file has more than 10 lines, so we successfully extract and print the 10th line

Example 2 — File with exactly 10 lines

$ Input: file.txt contains exactly 10 lines, line 10 is "last line"

› Output: last line

💡 Note: The file has exactly 10 lines, so line 10 exists and is printed

Example 3 — File with fewer than 10 lines

$ Input: file.txt contains only 5 lines

› Output:

💡 Note: The file has fewer than 10 lines, so there's no 10th line to print (empty output)

Constraints

The file may contain 0 to any number of lines
Each line can be up to 1000 characters
If file doesn't exist or has fewer than 10 lines, output should be empty

Visualization

Tap to expand

Asked in

U Unix Systems 30 D DevOps 25

The key insight is to use Unix text processing tools like sed, awk, or head/tail combinations to extract specific lines. Best approach is sed -n '10p' for direct line access. Time: O(n), Space: O(1)

Common Approaches

✓ AWK Line Processing

⏱️ Time: O(n) Space: O(1)

Use AWK's built-in NR (Number of Records) variable to track line numbers and print only when NR equals 10. AWK processes files line by line efficiently.

Head and Tail Combination

⏱️ Time: O(n) Space: O(1)

First extract the first 10 lines using head, then pipe to tail to get only the last line from those 10 lines. This gives us exactly the 10th line.

Sed Command

⏱️ Time: O(n) Space: O(1)

Use sed with line addressing to print only the 10th line. The '10p' command tells sed to print line 10, while '-n' suppresses default output.

AWK Line Processing — Algorithm Steps

Step 1: AWK reads each line and tracks line number in NR
Step 2: When NR==10, print the line and exit

Visualization

Tap to expand

Step-by-Step Walkthrough

AWK NR

Built-in line counter tracks current line

NR==10

Condition matches only line 10

Output the matching line

Code -

solution.c — C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char* solution(char* filename) {
    // Remove quotes if present
    if (filename[0] == '"') {
        filename++;
        int len = strlen(filename);
        if (filename[len-1] == '"') {
            filename[len-1] = '\0';
        }
    }
    
    char command[512];
    snprintf(command, sizeof(command), "awk 'NR==10' %s", filename);
    
    FILE* pipe = popen(command, "r");
    if (pipe == NULL) {
        return "";
    }
    
    static char result[1000];
    if (fgets(result, sizeof(result), pipe) != NULL) {
        // Remove trailing newline
        int len = strlen(result);
        if (len > 0 && result[len-1] == '\n') {
            result[len-1] = '\0';
        }
        pclose(pipe);
        return result;
    }
    
    pclose(pipe);
    return "";
}

int main() {
    char filename[256];
    if (fgets(filename, sizeof(filename), stdin)) {
        // Remove newline
        filename[strcspn(filename, "\n")] = 0;
        
        char* result = solution(filename);
        if (strlen(result) > 0) {
            printf("%s\n", result);
        } else {
            printf("\n");
        }
    }
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(n)

AWK reads through file until line 10 is found

✓ Linear Growth

Space Complexity

O(1)

AWK processes one line at a time without storing previous lines

✓ Linear Space

31.2K Views

Medium Frequency

~5 min Avg. Time

890 Likes

Ln 1, Col 1

Smart Actions

💡 Explanation

AI Ready

💡 Suggestion Tab to accept Esc to dismiss

// Output will appear here after running code

Code Editor Closed

Click the red button to reopen

Input & Output

Constraints

Visualization

Related Problems

Common Approaches

AWK Line Processing — Algorithm Steps

Visualization

Code -

Time & Space Complexity

Select Compiler