Linux Shell basic3 dd WC comm chmod ls

Generating files of any size

/dev/zerois A character special device, which infinitely returns the zero byte.

The above command would create a file called Junk.datathat is exactly 1MB in size. Let ' s go

Through the Parameters:ifstands for–inputfile, Ofstands for–outputfile, bsstands for

BYTES for a block, and countstands for the number of blocks of bsspecified to be copied.

DD If=/dev/zero of=junk.data bs=1m count=1

1+0 Records in

1+0 Records out

1048576 bytes (1.0 MB) copied, 0.00263553 s, 398 MB/s

Comm Command Demo:

[email protected] test]$ cat file1.txt file2.txt

1

2

3

4

1

2

4

5

[Email protected] test]$ Comm file1.txt file2.txt

1

2

3

4

5

[Email protected] test]$ Comm file1.txt file2.txt-1

1

2

4

5

[Email protected] test]$ Comm file1.txt file2.txt-2

1

2

3

4

[Email protected] test]$ Comm file1.txt file2.txt-3

3

5

[Email protected] test]$ Comm file1.txt file2.txt-3-1

5

-1 removes first column from output

-2 removes the second column

-3 removes the third column

[email protected] test]$ LL

Total 1052

-rw-rw-r--. 1 Hadoop Hadoop 08:34 all_txt_files.txt

-rw-rw-r--. 1 Hadoop Hadoop 8 Feb 03:29 file1.txt

-rw-rw-r--. 1 Hadoop Hadoop 8 Feb 03:29 file2.txt

-rw-rw-r--. 1 Hadoop hadoop 1048576 Feb 03:20 junk.data

-rw-rw-r--. 1 Hadoop Hadoop 02:06 mul_bank.txt

-rw-rw-r--. 1 Hadoop Hadoop 08:55 num.txt

Drwxrwxr-x. 2 Hadoop hadoop 4096 Feb 03:05 Sub

-rw-rw-r--. 1 Hadoop Hadoop 02:11 test.txt

"-"-if it is a regular file.

"D"-if it is a directory

"C"-for a character device

"B"-for a block device

"L"-if it is a symbolic link

"S"-for a socket

"P"-for a pipe

chmod u=rwx g=rw o=r filename

Here:

U =specifies user Permissions

G =specifies Group permissions

o =specifies Others permissions

chmod a+x filename

A statnd for all.

Read,write,and Execute permissions has a unique octal numbers as follows:

R--=4

-w-=2

--x=1

Touch is a command that can create blank files or modify the timestamp of files if they

Already exist.

Symbolic links is just pointers to other files.

Ln-s targetfilename (directory) link_name

Ln-s Test.txt Test_link.txt

counting number of lines, words, and characters in a file

$ wc-l File # count number of lines as follows:

$ wc-w File #count words number

$ head-10 filename

$ tail-10 filename

Head used to get the first n lines of the file.

Tail is used to get the last n lines of the file.

Linux Shell basic3 dd WC comm chmod ls