| Commands | Result |
|---|---|
| pwd | Print working directory |
| cd | change directory |
| ls | list directory contents |
| Shortcut | Result |
|---|---|
| cd | change the working directory to your home directory |
| cd - | change the working directory to previous working directory |
| cd ~user_name | change the working directory to the home directory of user_name |
| Commands | Result |
|---|---|
| ls | list directory contnet |
| file | Determine file type |
| less | View file contentre |
| Option | Long Option | Description |
|---|---|---|
| -a | --all | List all files those with name that begins with a period, which are normally hidden |
| -A | --almost-all | Like -a option above except it does not list '.' and '..' |
| -d | --directory | Use this option in conjunction with _l option to see detail about the directory rather than its content |
| -F | --classify | This option will append an indicator character to the end of each listed name. |
| -h | --human-readable | In long format listings, display file sizes in human readable format rather than in bytes. |
| -l | display results in long format | |
| -r | --reverse | Display the result in reverse order |
| -S | Sort results by file size | |
| -t | Sort by modification time |
| Command | Result |
|---|---|
| cp | Copy files and directories |
| mv | Move/rename file and directories |
| mkdir | Create directories |
| rm | Remove files and directories |
| ln | Create hard and symlink |
| Option | Description |
|---|---|
| -a, --archive | Copy the files and directories and all their attributes |
| -i, --interactive | Before overwriting an existing file, prompt the user |
| -r, --recursive | Recursively copy directories and their content |
| -u, --update | When copying files from one directory to another only copy files that are newer |
| -v, --verbose | Display informative message as the copy is performed |
| Option | Description |
|---|---|
| -i, --interactive | Before overwriting an existing file, prompt the user |
| -u, --update | When moving files from one directory to another only move files that are newer |
| -v, --verbose | Display informative message as the move is performed |
| Option | Description |
|---|---|
| -i, --interactive | Before deleting an existing file, prompt the user |
| -r, --recursive | Recursively delete directories and their content |
| -f, --force | Ignore nonexistent files and do not prompt |
| -v, --verbose | Display informative message as the deletion is performed |
| Wildcard | Meaning |
|---|---|
| * | Matches any character |
| ? | Matches any single character |
| [characters] | Matches any character that is a member of the set character |
| [!characters] | Matches any character that is not a member of the set character |
| [[:class:]] | Matches any character that is a member of the specified class |
| Character Class | Meaning |
|---|---|
| [:alnum:] | Matches any alphanumeric character |
| [:alpha:] | Matches any alphabetic character |
| [:digit:] | Matches any numeral |
| [:lower:] | Matches any lowercase letter |
| [:upper:] | Matches any uppercase letter |
| Pattern | Matches |
|---|---|
| * | All files |
| g* | All files beginning with 'g' |
| b*.txt | Any file beginning with 'b' followed by any character and ending with '.txt' |
| Data??? | All file beginning with 'Data' followed by exactly three character |
| [abc]* | Any file beginning with either 'a' or 'b' or 'c' |
| BACKUP.[0-9][0-9][0-9] | Any file beginning with 'BACKUP.' followed by three numerals |
| [[:upper:]]* | Any file beginning with an uppercase letter |
| [![:digit:]]* | Any file not beginning with a numeral |
| *[[:lower]123] | Any file ending with a lowercase letter or the numerals 1, 2, or 3 |
| Command | Meaning |
|---|---|
| type | Indicate how a command name is intepreted |
| which | Display which executable program will be executed |
| help | Get help for shell builtin |
| man | Display a command's manual page |
| apropos | Display a list of appropriate commands |
| info | Display a command's info entry |
| whatis | Display a very brief description of a command |
| alias | Create an alias for a command |
- An executable program
- A command built into the shell itself
- A shell function
- An alias
[me@linuxbox ~]$ type type
type is a shell builtin
[me@linuxbox ~]$ type ls
ls is aliased to `ls --color=tty'
[me@linuxbox ~]$ type cp
cp is /bin/cp
Sometimes there is more than one version of executable program installed on a system, to know version of program is executing which commands comes in.
[me@linuxbox ~]$ which ls
/bin/ls
Many commands program support a --help option that display a description of the command's supported syntax and option.
[me@linuxbox ~]$ man program_name
Section | Contents 1 | User commands 2 | Programming interface for kernal system calls 3 | Programming interface to the C library 4 | Special files such as device nodes and driver 5 | File formats 6 | Games and amusements such as screensaver 7 | Miscellaneous 8 | System administration commands
Sometime we need to look at specific section of man page
[me@linuxbox ~]$ man section program_name
[me@linuxbox ~]$ apropos passwd
chgpasswd (8) - update group passwords in batch mode
chpasswd (8) - update passwords in batch mode
fgetpwent_r (3) - get passwd file entry reentrantly
getpwent_r (3) - get passwd file entry reentrantly
gpasswd (1) - administer /etc/group and /etc/gshadow
grub-mkpasswd-pbkdf2 (1) - generate hashed password for GRUB
pam_localuser (8) - require users to be listed in /etc/passwd
passwd (1) - change user password
passwd (1ssl) - compute password hashes
passwd (5) - the password file
passwd2des (3) - RFS password encryption
update-passwd (8) - safely update /etc/passwd, /etc/shadow and /etc/group
Note: the man command with -k option perform the exact same function as apropos
[me@linuxbox ~]$ whatis ls
ls (1) - list directory contents
Alternative to man page. Info page are hyperlinked much like web page. A hyperlink can be identified by its leading asterisk and is activated by placing a cursor on it and hit enter key.
To invoke info type "info" followed optionally by the name of the program. Below is a table of commands used to control the reader while displaying an info page.
Command | Action ? | Display command help PgUp or Backspace | Display previous page PgDn or Space | Display next page n | Next - Display next node p | Previous - Display previous node u | Up - Display the parent node of the currently displayed node, usually a menu Enter | Follow the hyperlink at the cursor location q | Quit
Many software package installed on your system have documentation files residing in the /usr/share/doc directory. Most of these are stored in plain text format and can be viewed with less. Some of the files are HTML format and can be viewed in browser. We may encounter some .gz files these are compressed files and can be view with zless
alias name='string'
[me@linuxbox ~]$ alias foo='cd /usr; ls; cd -'
[me@linuxbox ~]$ alias
alias l.='ls -d .* --color=tty'
alias ll='ls -l --color=tty'
alias ls='ls --color=tty'
to unalias a command
unalias name
| Commands | Result |
|---|---|
| cat | Concatenate files |
| sort | Sort lines of text |
| uniq | Report or omit repeated lines |
| grep | Print lines matching a pattern |
| wc | Print newline, word and byte count for each files |
| head | Output the first part of file |
| tail | Output the last part of file |
| tee | Read from standard input and write to standard output and files |
[me@linuxbox ~]$ ls -l /usr/bin > ls-output.txt
when you do the above way the file is overwritten means that any content in file will replace with new output of program, for appending use >> instead of >
[me@linuxbox ~]$ ls -l /usr/bin >> ls-output.txt
Standard error we must refer to its file descriptor. While we have referred to the first three of these file streams as standard input, output and error, the shell references them internally as file descriptors 0, 1 and 2, respectively
Since standard error is the same as file descriptor number 2, we can redirect standard error with this notation:
[me@linuxbox ~]$ ls -l /bin/usr 2> ls-error.txt
[me@linuxbox ~]$ ls -l /bin/usr > ls-output.txt 2>&1
Recent versions of bash provide a second, more streamlined method for performing this combined redirection:
[me@linuxbox ~]$ ls -l /bin/usr &> ls-output.txt
Sometimes “silence is golden,” and we don't want output from a command, we just want to throw it away. This applies particularly to error and status messages. The system provides a way to do this by redirecting output to a special file called “/dev/null”. This file is a system device called a bit bucket which accepts input and does nothing with it. To suppress error messages from a command, we do this:
[me@linuxbox ~]$ ls -l /bin/usr 2> /dev/null
If cat is not given any arguments, it reads from standard input and since standard input is, by default, attached to the keyboard, it's waiting for us to type something! Try adding the following text and pressing Enter:
[me@linuxbox ~]$ cat > lazy_dog.txt
The quick brown fox jumped over the lazy dog.
Using the “<” redirection operator, we change the source of standard input from the keyboard to the file lazy_dog.txt. We see that the result is the same as passing a single filename argument. This is not particularly useful compared to passing a filename argument, but it serves to demonstrate using a file as a source of standard input. Other commands make better use of standard input, as we shall soon see.
[me@linuxbox ~]$ cat < lazy_dog.txt
The quick brown fox jumped over the lazy dog.
command1 | command2
[me@linuxbox ~]$ ls /bin /usr/bin | sort | less
[me@linuxbox ~]$ ls /bin /usr/bin | sort | uniq | less
if you want to see duplicate instead use -d option
[me@linuxbox ~]$ ls /bin /usr/bin | sort | uniq -d | less
[me@linuxbox ~]$ wc ls-output.txt
7902 64566 503634 ls-output.txt
In this case it print three number: lines, words, bytes contained in ls-output.txt. The -l option can be used to output only lines
[me@linuxbox ~]$ ls /bin /usr/bin | sort | uniq | wc -l
2728
grep is one of the powerful program. it use to find text pattern within files.
grep pattern [file...]
The patterns that grep can match can be very complex, you can use regular expression also here
[me@linuxbox ~]$ ls /bin /usr/bin | sort | uniq | grep zip
bunzip2
bzip2
gunzip
gzip
unzip
zip
zipcloak
zipgrep
zipinfo
zipnote
zipsplit
There are couple of handy options for grep: -i which causes grep to ignore case when performing the search, -v which print lines that dont match the pattern
Sometime you don't want the full output from a command. You may only want the first few lines or the last few lines. The head command prints the first ten lines of a file and the tail command prints the last ten lines. By default, both commands print ten lines of text, but this can be adjusted with the “-n” option:
[me@linuxbox ~]$ head -n 5 ls-output.txt
total 343496
-rwxr-xr-x 1 root root 31316 2007-12-05 08:58 [
-rwxr-xr-x 1 root root 8240 2007-12-09 13:39 411toppm
-rwxr-xr-x 1 root root 111276 2007-11-26 14:27 a2p
-rwxr-xr-x 1 root root 25368 2006-10-06 20:16 a52dec
[me@linuxbox ~]$ tail -n 5 ls-output.txt
-rwxr-xr-x 1 root root 5234 2007-06-27 10:56 znew
-rwxr-xr-x 1 root root 691 2005-09-10 04:21 zonetab2pot.py
-rw-r--r-- 1 root root 930 2007-11-01 12:23 zonetab2pot.pyc
-rw-r--r-- 1 root root 930 2007-11-01 12:23 zonetab2pot.pyo
lrwxrwxrwx 1 root root 6 2016-01-31 05:22 zsoelim -> soelim
These can be used with pipelines as well:
[me@linuxbox ~]$ ls /usr/bin | tail -n 5
tail has an option which allows you to view files in real-time. This is useful for watching the progress of log files as they are being written. In the following example, we will look at the messages file in /var/log (or the /var/log/syslog file if messages is missing). Superuser privileges are required to do this on some Linux distributions, since the /var/log/messages file may contain security information:
[me@linuxbox ~]$ tail -f /var/log/messages
Feb 8 13:40:05 twin4 dhclient: DHCPACK from 192.168.1.1
Feb 8 13:40:05 twin4 dhclient: bound to 192.168.1.4 -- renewal in
1652 seconds.
Feb 8 13:55:32 twin4 mountd[3953]: /var/NFSv4/musicbox exported to
both 192.168.1.0/24 and twin7.localdomain in
192.168.1.0/24,twin7.localdomain
...
In keeping with our plumbing metaphor, Linux provides a command called tee which creates a “tee” fitting on our pipe. The tee program reads standard input and copies it to both standard output (allowing the data to continue down the pipeline) and to one or more files. This is useful for capturing a pipeline's contents at an intermediate stage of processing. Here we repeat one of our earlier examples, this time including tee to capture the 64 Pipelines entire directory listing to the file ls.txt before grep filters the pipeline's contents:
[me@linuxbox ~]$ ls /usr/bin | tee ls.txt | grep zip
bunzip2
bzip2
gunzip
gzip
unzip
zip
zipcloak
zipgrep
zipinfo
zipnote
zipsplit
When I am asked to explain the difference between Windows and Linux, I often use a toy analogy. Windows is like a Game Boy. You go to the store and buy one all shiny new in the box. You take it home, turn it on and play with it. Pretty graphics, cute sounds. After a while though, you get tired of the game that came with it so you go back to the store and buy another one. This cycle repeats over and over. Finally, you go back to the store and say to the person behind the counter, “I want a game that does this!” only to be told that no such game exists because there is no “market demand” for it. Then you say, “But I only need to change this one thing!” The person behind the counter says you can't change it. The games are all sealed up in their cartridges. You discover that your toy is limited to the games that others have decided that you need and no more. Linux, on the other hand, is like the world's largest Erector Set. You open it up and it's just a huge collection of parts. A lot of steel struts, screws, nuts, gears, pulleys, motors, and a few suggestions on what to build. So you start to play with it. You build one of the suggestions and then another. After a while you discover that you have your own ideas of what to make. You don't ever have to go back to the store, as you already have everything you need. The Erector Set takes on the shape of your imagination. It does what you want. Your choice of toys is, of course, a personal thing, so which toy would you find more satisfying?
| Command | Result |
|---|---|
| echo | Display a line of text |
Each time we type a command and press the enter key, bash performs several processes upon the text before it carries out our command. We have seen a couple of cases of how a simple character sequence, for example “*”, can have a lot of meaning to the shell. The process that makes this happen is called expansion. With expansion, we enter something and it is expanded into something else before the shell acts upon it. To demonstrate what we mean by this, let's take a look at the echo command. echo is a shell builtin that performs a very simple task. It prints out its text arguments on standard output:
[me@linuxbox ~]$ echo this is a test
this is a testThat's pretty straightforward. Any argument passed to echo gets displayed. Let's try another example:
[me@linuxbox ~]$ echo *
Desktop Documents ls-output.txt Music Pictures Public Templates
Videos