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C program to print given number of lines of a file (like head command in Linux)

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mahmoud2506

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2022-05-04

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C program to print given number of lines of a file (like head command in Linux)

This program will print the given number of lines of a file, just like Head command in Linux. Head command displays only the given number of lines of a given file name. Same as head command in this program you have to supply file name then number of lines.
The syntax of executing this program
./program-name file-name N
Here N is the number of lines, if available lines in the file are less than N, program will display all lines of the file.

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mahmoud2506

2022-05-04

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C program to print given number of lines of a file

linux head command implementation

//c program to print given number of lines from beginning of a file
//file name and number of lines must be supply as command line argument
 
#include <stdio.h>
 
int main(int argc, char * argv[])
{
    FILE    *   fp;             // file pointer
    char    *   line = NULL;
    int         len  = 0;
 
    int cnt = 0;    
 
    if( argc < 3)
    {
        printf("Insufficient Arguments!!!\n");
        printf("Please use "program-name file-name N" format.\n");
        return -1;
    }
 
    // open file
    fp = fopen(argv[1],"r");
 
    // checking for file is exist or not
    if( fp == NULL )
    {
        printf("\n%s file can not be opened !!!\n",argv[1]);
        return 1;   
    }
 
    // read lines from file one by one
    while (getline(&line, &len, fp) != -1)
    {
        cnt++;
        if ( cnt > atoi(argv[2]) )
            break;
 
        printf("%s",line); fflush(stdout);
    }
     
    // close file
    fclose(fp);
 
    return 0;
}

Output

First Run:
Terminal command : ./prg1 file1.txt
Insufficient Arguments!!!
Please use "program-name file-name N" format.

Second Run:
Terminal command : ./prg1 file1.txt 5
this is line 1.
this is line 2.
this is line 3.
this is line 4.
this is line 5.

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