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Linux command--view file contents

cat: display file content from the first line;

tac: display from the last line, you can see that tac and cat are in reverse alphabetic order; Br>

nl: output line number when displayed;

more: one page to display the contents of the file;

less similar to more, but it can page forward;

head: just look at the first few lines;

tail: just look at the last few lines;

od: binary way to read the file;

Command Details

cat –n filename # Output line number when displayed, same as nl

cat is a shorthand for Concatenate (continuous), the main function is to have a file The content is continuously displayed on the screen.

tac (reverse display) is opposite to the display direction of Cat

nl (adding line number when displaying) It is a one-time display of data to the screen with cat, tac, etc. Page turning

Linux commands--modifying file time and creating new files

Three time states of files

Modification time(mtime) modification time

status time (ctime) status time

access time (atime) access time

The time to view with the ls -l command is mtime

touch -a only modify access Time

touch –c only modify the time without creating a file

touch –m only modify mtime

The usual use of the touch command is:

Create an empty file

to modify a file date to the current date (mtime and atime)

the default file permissions

If the user establishes When the file is used, there is no executable (x) permission by default, that is, only two permissions of rw (-rw-rw-rw 666)

If the user establishes the "directory", because x is possible or not Enter this directory, This default permissions are open to all, namely 777 (drwxrwxrwx)

umask specified is & ldquo; the default values need to lose privileges & rdquo ;. Since r, w, and x are 4, 2, and 1, respectively, that is, when the write permission is to be removed, 2 is entered, and when the read permission is removed, 4 is entered. Because umask is 022, user does not remove the attribute, but the attributes of group and others are removed by 2 (that is, the attribute of w)

When the user creates a file: -rw- R--r--

When creating a directory: drwxr-xr-x

How to modify umask, if you want to change to 002

Use umask command 002 to

hidden file attribute

chattr (hidden attribute setting file)

parameters used

chattr & ndash; a : After setting, this file can only add data, not delete data

chattr –i : it can make a file "cannot be deleted, renamed, set connection, can not be written or added Data”.

lsattr (hidden attribute display file)

lsattr & ndash; a: the hidden file property page is displayed.

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