Question

1). Please explain the commands head, tail, cat, tac, strings. And also run these commands in the Linux machine. (Use your own Id’s)

Answer 1

1) head : It is a command used to print first N lines from a file to terminal server (Output window).

eg. Fruits.txt

Orange

Mango

Guava

Banana

WaterMelon

Papaya

Cherry

Strawberry

Apple

MuskMelon

head -5 Fruits.txt : This command prints first 5 lines of the file Fruits.txt.

Output :

Orange

Mango

Guava

Banana

WaterMelon

eg2. head Fruits.txt : By default head command prints first 10 lines of the file.So the output will be first 10 lines of the file Fruits.txt.

2) tail : It is a command used to print last N lines from a file to terminal server (Output window).

eg. tail -5 Fruits.txt : This command prints last 5 lines of the file Fruits.txt.

Output :

Papaya

Cherry

Strawberry

Apple

MuskMelon

eg2. tail Fruits.txt : By default head command prints last 10 lines of the file.So the output will be last 10 lines of the file Fruits.txt.

3) cat : It opens the file and prints it on standard output.

a) cat Fruits.txt : This command displays content of file.

Output :
Orange

Mango

Guava

Banana

WaterMelon

Papaya

Cherry

Strawberry

Apple

MuskMelon

b) cat File1.txt File2.txt > File3.txt : This command concatenates content of 2 files and store it in output file File3.txt

File1.txt
Hello

File2.txt
World

File3.txt
Hello
World

4) tac : It concatenates and prints content of file just like cat but in reverse order (ie. last line first) on standard output
eg:

File1.txt

Sam
Paul
Harry

tac File1.txt

OUTPUT :

Harry
Paul
Sam

5) strings : It is used to view all the printable strings/characters from the binary file (non text files).
eg. Let us create a simple c program
$ cat welcome.c
# include <stdio.h>

main()
{
char a[]="strings program";
printf("Welcome to Sample program\n");
system("ls");
printf("%s",a);
}

Create an object file for this c file
$ cc -o welcome welcome.c

$ strings welcome
Output:
/lib64/ld-linux-x86-64.so.2
__gmon_start__
libc.so.6
puts
printf
system
__libc_start_main
GLIBC_2.2.5
l$ L
t$(L
|$0H
Welcome to sample program
strings program