Tenth Line - Practice Coding Problems

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

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Understanding the Visualization

Input File

Text file with multiple lines, need line 10

Process

Use shell commands to locate 10th line

Output

Print only the 10th line content

Key Takeaway

🎯 Key Insight: Use Unix line addressing tools to directly access specific line numbers without reading/storing entire file content

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

Approach	Time	Space	Notes
✓ Sed Command	O(n)	O(1)	Use sed to directly extract the 10th line with address notation
AWK Line Processing	O(n)	O(1)	Use AWK with line number variable to print only the 10th line
Head and Tail Combination	O(n)	O(1)	Use head to get first 10 lines, then tail to get the last one

Sed Command — Algorithm Steps

Step 1: Use sed -n '10p' to select line 10
Step 2: Print only that specific line

Visualization

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Step-by-Step Walkthrough

Sed -n

Suppress default output

10p

Print only line 10

Result

Output the 10th line directly

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), "sed -n '10p' %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)

Sed reads through the file until it reaches line 10

✓ Linear Growth

Space Complexity

O(1)

Sed processes the file line by line without storing content

✓ Linear Space

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Smart Actions

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Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Sed Command — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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