In this part,I will show you how to do some arithmetic calculation in Bash.
1.COMMAND:
expr
DESCRIPTION:
Print the value of EXPRESSION to standard output.
SYNOPSIS:
expr EXPRESSION
Example:
root@piniheaven:~# expr 1 + 1
2
root@piniheaven:~# expr 2 - 1
1
root@piniheaven:~# expr 4 / 2
2
root@piniheaven:~# expr 2 \* 2 #Tip: when you want to do some multiplication,you should use backslash
4
2.COMMAND:
let
DESCRIPTION:
carry out arithmetic operations on variables.
Example:
root@piniheaven:~# let " val=(1+1)*2" # will compute 2 times 2 and assign the result to the variable "val".
root@piniheaven:~# echo $val #print variable val
4
2014年3月19日星期三
Linux Commands for Beginners lesson 18 -- Finding Files
In this part, I demonstrate how to find files.
1.COMMAND:
find
DESCRIPTION:
search for files in a directory hierarchy
SYNOPSIS:
find <path> <fileName>
OPTION:
-mtime n File's data was last modified n*24 hours ago.
-name Base of file name
Example:
If you remember the file's name,you can specify a path to find it out.
root@piniheaven:~# find /root/ -name find.txt
/root/tutorial/find.txt
Even you can't remember what the exactly file name is,you still can find it out.
root@piniheaven:~# find /root/ -name fin*
/root/tutorial/find.txt
Find out files that was last modified 24 hours ago.
root@piniheaven:~# find /root/tutorial/ -mtime -1
/root/tutorial/
/root/tutorial/.find.txt.swp
/root/tutorial/poem.txt
/root/tutorial/find.txt
1.COMMAND:
find
DESCRIPTION:
search for files in a directory hierarchy
SYNOPSIS:
find <path> <fileName>
OPTION:
-mtime n File's data was last modified n*24 hours ago.
-name Base of file name
Example:
If you remember the file's name,you can specify a path to find it out.
root@piniheaven:~# find /root/ -name find.txt
/root/tutorial/find.txt
Even you can't remember what the exactly file name is,you still can find it out.
root@piniheaven:~# find /root/ -name fin*
/root/tutorial/find.txt
Find out files that was last modified 24 hours ago.
root@piniheaven:~# find /root/tutorial/ -mtime -1
/root/tutorial/
/root/tutorial/.find.txt.swp
/root/tutorial/poem.txt
/root/tutorial/find.txt
Linux Commands for Beginners lesson 17 -- Head and Tail Command
In this part, I go over both the head and tail commands.
1.COMMAND:
head
DESCRIPTION:
Print the first 10 lines of FILE to standard output.
SYNOPSIS:
head [OPTION]... [FILE]...
OPTION:
-n, --lines
print the first n lines instead of the first 10;
2.COMMAND:
tail
DESCRIPTION:
Print the last 10 lines of FILE to standard output.
SYNOPSIS:
tail [OPTION]... [FILE]...
OPTION:
-n, --lines output the last K lines, instead of the last 10;
Examples:
root@piniheaven:~/tutorial# ls
poem.txt
root@piniheaven:~/tutorial# head poem.txt # Print the first 10 lines of poem.txt to standard output.
nt you to know
one thing.
You know how this is:
if I look
at the crystal moon, at the red branch
of the slow autumn at my window,
if I touch
near the fire
the impalpable ash
root@piniheaven:~/tutorial# head -4 poem.txt # Print the first 4 lines of poem.txt to standard output.
nt you to know
one thing.
You know how this is:
root@piniheaven:~/tutorial# tail poem.txt # Print the last 10 lines of poem.txt to standard output.
you feel that you are destined for me
with implacable sweetness,
if each day a flower
climbs up to your lips to seek me,
ah my love, ah my own,
in me all that fire is repeated,
in me nothing is extinguished or forgotten,
my love feeds on your love, beloved,
and as long as you live it will be in your arms
without leaving mine
root@piniheaven:~/tutorial# tail -3 poem.txt # Print the last 3 lines of poem.txt to standard output.
my love feeds on your love, beloved,
and as long as you live it will be in your arms
without leaving mine
1.COMMAND:
head
DESCRIPTION:
Print the first 10 lines of FILE to standard output.
SYNOPSIS:
head [OPTION]... [FILE]...
OPTION:
-n, --lines
print the first n lines instead of the first 10;
2.COMMAND:
tail
DESCRIPTION:
Print the last 10 lines of FILE to standard output.
SYNOPSIS:
tail [OPTION]... [FILE]...
OPTION:
-n, --lines output the last K lines, instead of the last 10;
Examples:
root@piniheaven:~/tutorial# ls
poem.txt
root@piniheaven:~/tutorial# head poem.txt # Print the first 10 lines of poem.txt to standard output.
nt you to know
one thing.
You know how this is:
if I look
at the crystal moon, at the red branch
of the slow autumn at my window,
if I touch
near the fire
the impalpable ash
root@piniheaven:~/tutorial# head -4 poem.txt # Print the first 4 lines of poem.txt to standard output.
nt you to know
one thing.
You know how this is:
root@piniheaven:~/tutorial# tail poem.txt # Print the last 10 lines of poem.txt to standard output.
you feel that you are destined for me
with implacable sweetness,
if each day a flower
climbs up to your lips to seek me,
ah my love, ah my own,
in me all that fire is repeated,
in me nothing is extinguished or forgotten,
my love feeds on your love, beloved,
and as long as you live it will be in your arms
without leaving mine
root@piniheaven:~/tutorial# tail -3 poem.txt # Print the last 3 lines of poem.txt to standard output.
my love feeds on your love, beloved,
and as long as you live it will be in your arms
without leaving mine
Linux Commands for Beginners lesson 16 -- The Watch Command
In this part, I talk about the watch command.
DESCRIPTION :
execute a program periodically, showing output fullscreen
SYNOPSIS :
watch [option] <command>
OPTION :
-n : By default, the program is run every 2 seconds; use -n to specify a different interval.
command: any linux command you want to type
Example :
[piniheaven@localhost ~]$ watch -n 10 free -m #Every 10.0s free -mwill be executed automatically
Every 10.0s: free -m Tue Sep 3 17:48:56 2013
total used free shared buffers cached
Mem: 5690 1388 4301 0 82 620
-/+ buffers/cache: 685 5004
Swap: 0 0 0
1.COMMAND :
watchDESCRIPTION :
execute a program periodically, showing output fullscreen
SYNOPSIS :
watch [option] <command>
OPTION :
-n : By default, the program is run every 2 seconds; use -n to specify a different interval.
command: any linux command you want to type
Example :
[piniheaven@localhost ~]$ watch -n 10 free -m #Every 10.0s free -mwill be executed automatically
Every 10.0s: free -m Tue Sep 3 17:48:56 2013
total used free shared buffers cached
Mem: 5690 1388 4301 0 82 620
-/+ buffers/cache: 685 5004
Swap: 0 0 0
Linux Commands for Beginners lesson 15 -- du,df,free commands
In this part, I talk about viewing system resources.
1.COMMAND :
df
DESCRIPTON :
report file system disk space usage
SYNOPSIS :
df [OPTION]... [FILE]...
OPTION :
-h, --human-readable
Example :
[piniheaven@localhost ~]$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 15G 5.4G 9.0G 38% /
tmpfs 2.8G 884K 2.8G 1% /dev/shm
2.COMMAND :
du
DESCRIPTION :
estimate file space
SYNOPSIS :
du [OPTION]... [FILE]...
OPTION :
-s, --summarize
display only a total for each argument
-h, --human-readable print sizes in human readable format (e.g., 1K 234M 2G)
Example :
[piniheaven@localhost ~]$ ls
Desktop Documents Music Public SolftWare tutorial
distribute-0.6.49 Downloads Pictures Python-2.7.3 Templates Videos
[piniheaven@localhost ~]$ du -sh Videos
254MVideos
3.COMMAND :
free
DESCRIPTION :
Display amount of free and used memory in the system
SYNOPSIS :
free [-m]
OPTION :
-m switch displays it in megabytmegabytes.
Example :
[piniheaven@localhost ~]$ free-m
total used free shared buffers cached
Mem: 5690 1736 3953 0 74 615
-/+ buffers/cache: 1046 4644
Swap: 0 0 0
Explanation:
Actual Used Physical Memory (Memory Used by Apps) :1046 MB
Actual Free Physical Memory (Memory Available For Apps) :4644 MB
1.COMMAND :
df
DESCRIPTON :
report file system disk space usage
SYNOPSIS :
df [OPTION]... [FILE]...
OPTION :
-h, --human-readable
Example :
[piniheaven@localhost ~]$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 15G 5.4G 9.0G 38% /
tmpfs 2.8G 884K 2.8G 1% /dev/shm
2.COMMAND :
du
DESCRIPTION :
estimate file space
SYNOPSIS :
du [OPTION]... [FILE]...
OPTION :
-s, --summarize
display only a total for each argument
-h, --human-readable print sizes in human readable format (e.g., 1K 234M 2G)
Example :
[piniheaven@localhost ~]$ ls
Desktop Documents Music Public SolftWare tutorial
distribute-0.6.49 Downloads Pictures Python-2.7.3 Templates Videos
[piniheaven@localhost ~]$ du -sh Videos
254MVideos
3.COMMAND :
free
DESCRIPTION :
Display amount of free and used memory in the system
SYNOPSIS :
free [-m]
OPTION :
-m switch displays it in megabytmegabytes.
Example :
[piniheaven@localhost ~]$ free-m
total used free shared buffers cached
Mem: 5690 1736 3953 0 74 615
-/+ buffers/cache: 1046 4644
Swap: 0 0 0
Explanation:
Actual Used Physical Memory (Memory Used by Apps) :1046 MB
Actual Free Physical Memory (Memory Available For Apps) :4644 MB
If you want to know more about what is the difference between buffer and cache memory,you can click following link.
Linux Commands for Beginners lesson 14 -- the grep command
In this part,I wil show you the basis of Regular Expressions and the grep command
1.Command:
grep
DESCRIPTION:
print lines matching a pattern
SYNOPSIS:
grep [OPTIONS] PATTERN [FILE...]
OPTION:
-n, --line-number print line number with output lines
Regular expressions made up of anchors,character sets,modifiers
Anchors:specify the position
^ :at the beginnig of a line
$ :at the end of a line
Tips:If ^ is not placed at the beginning ,or $ at the end,the two won't act as anchors anymore
character sets:what is seached
Example:
root@piniheaven:~/tutorial# ls
A Girl.txt
root@piniheaven:~/tutorial# cat -n A\ Girl.txt
1 the tree has entered my hands
2 the sap has ascended my arms
3 the tree has grown in my breast-
4 downward
5 the branches grow out of me, like arms
6
7 tree you are
8 moss you are
9 you are violets with wind above them
10 a child - so high - you are
11 and all this is folly to the world
print lines contain words "tree"
root@piniheaven:~/tutorial# grep 'tree' A\ Girl.txt
the tree has entered my hands
the tree has grown in my breast-
tree you are
print lines contain word "tree" and print which line they are in
root@piniheaven:~/tutorial# grep -n 'tree' A\ Girl.txt
1:the tree has entered my hands
3:the tree has grown in my breast-
7:tree you are
print lines start with word "tree" and print which line they are in
root@piniheaven:~/tutorial# grep -n ^'tree' A\ Girl.txt
7:tree you are
print lines contain word "are" and print which line they are in
root@piniheaven:~/tutorial# grep -n 'are' A\ Girl.txt
7:tree you are
8:moss you are
9:you are violets with wind above them
10:a child - so high - you are
print lines end with word "are" and print which line they are in
root@piniheaven:~/tutorial# grep -n 'are'$ A\ Girl.txt
7:tree you are
8:moss you are
10:a child - so high - you are
Matching Character Sets
--"abc" finds lines with "abc" in them
--match any character with "."(dot)
--specify a range with []
[123] - lines that contain 1,2 or 3
[0-9] - lines that contain at least a number
[A-Za-z0-9] - lines that contain at leas a letters or a numbers
Example:
Find words start with letter 'm' and follow with a any character
root@piniheaven:~/tutorial# grep -n 'm.' A\ Girl.txt
1:the tree has entered my hands
2:the sap has ascended my arms
3:the tree has grown in my breast-
5:the branches grow out of me, like arms
8:moss you are
Find words start with letter 'a' or 'b'
root@piniheaven:~/tutorial# grep -n ^'[ad]' A\ Girl.txt
4:downward
10:a child - so high - you are
11:and all this is folly to the world
print lines start with a letter range from 'a' to 'm'
root@piniheaven:~/tutorial# grep -n ^'[a-m]' A\ Girl.txt
4:downward
8:moss you are
10:a child - so high - you are
11:and all this is folly to the world
Tips:
If you want to search for "[" or "]",you should use backslash "\"
Example:
[\]] - search lines with "]" in them
modifiers:specify how many times the previous charater set is repeated
* - matches zero or more copies of the chars
[]\{1,4\} - lines that have between 1 to 4 mathes
\<word\> - searches for a specific and separate word
Example:
root@piniheaven:~/tutorial# ls
A Girl.txt essay.txt
root@piniheaven:~/tutorial# cat -n essay.txt
1 a
2 aa
3 aaa
4 aaaa
5 aaaaa
6 aaaaaa
7
8 abc
9 abbc
10 abcc
print lines contain word that mach [b-c][b-c]
root@piniheaven:~/tutorial# grep -n '[b-c]\{2,3\}' essay.txt
8:abc
9:abbc
10:abcc
If you want to just search specify word,following command failed to work.
root@piniheaven:~/tutorial# grep -n 'aa' essay.txt
2:aa
3:aaa
4:aaaa
5:aaaaa
6:aaaaaa
therefore,you can type command like this
root@piniheaven:~/tutorial# grep -n '\<aa\>' essay.txt
2:aa
1.Command:
grep
DESCRIPTION:
print lines matching a pattern
SYNOPSIS:
grep [OPTIONS] PATTERN [FILE...]
OPTION:
-n, --line-number print line number with output lines
Regular expressions made up of anchors,character sets,modifiers
Anchors:specify the position
^ :at the beginnig of a line
$ :at the end of a line
Tips:If ^ is not placed at the beginning ,or $ at the end,the two won't act as anchors anymore
character sets:what is seached
Example:
root@piniheaven:~/tutorial# ls
A Girl.txt
root@piniheaven:~/tutorial# cat -n A\ Girl.txt
1 the tree has entered my hands
2 the sap has ascended my arms
3 the tree has grown in my breast-
4 downward
5 the branches grow out of me, like arms
6
7 tree you are
8 moss you are
9 you are violets with wind above them
10 a child - so high - you are
11 and all this is folly to the world
print lines contain words "tree"
root@piniheaven:~/tutorial# grep 'tree' A\ Girl.txt
the tree has entered my hands
the tree has grown in my breast-
tree you are
print lines contain word "tree" and print which line they are in
root@piniheaven:~/tutorial# grep -n 'tree' A\ Girl.txt
1:the tree has entered my hands
3:the tree has grown in my breast-
7:tree you are
print lines start with word "tree" and print which line they are in
root@piniheaven:~/tutorial# grep -n ^'tree' A\ Girl.txt
7:tree you are
print lines contain word "are" and print which line they are in
root@piniheaven:~/tutorial# grep -n 'are' A\ Girl.txt
7:tree you are
8:moss you are
9:you are violets with wind above them
10:a child - so high - you are
print lines end with word "are" and print which line they are in
root@piniheaven:~/tutorial# grep -n 'are'$ A\ Girl.txt
7:tree you are
8:moss you are
10:a child - so high - you are
Matching Character Sets
--"abc" finds lines with "abc" in them
--match any character with "."(dot)
--specify a range with []
[123] - lines that contain 1,2 or 3
[0-9] - lines that contain at least a number
[A-Za-z0-9] - lines that contain at leas a letters or a numbers
Example:
Find words start with letter 'm' and follow with a any character
root@piniheaven:~/tutorial# grep -n 'm.' A\ Girl.txt
1:the tree has entered my hands
2:the sap has ascended my arms
3:the tree has grown in my breast-
5:the branches grow out of me, like arms
8:moss you are
Find words start with letter 'a' or 'b'
root@piniheaven:~/tutorial# grep -n ^'[ad]' A\ Girl.txt
4:downward
10:a child - so high - you are
11:and all this is folly to the world
print lines start with a letter range from 'a' to 'm'
root@piniheaven:~/tutorial# grep -n ^'[a-m]' A\ Girl.txt
4:downward
8:moss you are
10:a child - so high - you are
11:and all this is folly to the world
Tips:
If you want to search for "[" or "]",you should use backslash "\"
Example:
[\]] - search lines with "]" in them
modifiers:specify how many times the previous charater set is repeated
* - matches zero or more copies of the chars
[]\{1,4\} - lines that have between 1 to 4 mathes
\<word\> - searches for a specific and separate word
Example:
root@piniheaven:~/tutorial# ls
A Girl.txt essay.txt
root@piniheaven:~/tutorial# cat -n essay.txt
1 a
2 aa
3 aaa
4 aaaa
5 aaaaa
6 aaaaaa
7
8 abc
9 abbc
10 abcc
print lines contain word that mach [b-c][b-c]
root@piniheaven:~/tutorial# grep -n '[b-c]\{2,3\}' essay.txt
8:abc
9:abbc
10:abcc
If you want to just search specify word,following command failed to work.
root@piniheaven:~/tutorial# grep -n 'aa' essay.txt
2:aa
3:aaa
4:aaaa
5:aaaaa
6:aaaaaa
therefore,you can type command like this
root@piniheaven:~/tutorial# grep -n '\<aa\>' essay.txt
2:aa
Linux Commands for Beginners lesson 13-- which and whatis commands
In this tutorial, I talk about the which and whatis commands.
1.COMMAND:
which
DESCRIPTION:
locate a command
SYNOPSIS
which commandName
Example:
piniheaven@fish:~$ which ls
/bin/ls
piniheaven@fish:~$ which nano
/usr/bin/nano
2.COMMAND:
whatis
DESCRIPTION:
display manual page descriptions
SYNOPSIS
whatis commandName
Example:
piniheaven@fish:~$ whatis firefox
firefox (1) - a free and open source web browser from Mozilla
piniheaven@fish:~$ whatis ls
ls (1) - list directory contents
1.COMMAND:
which
DESCRIPTION:
locate a command
SYNOPSIS
which commandName
Example:
piniheaven@fish:~$ which ls
/bin/ls
piniheaven@fish:~$ which nano
/usr/bin/nano
2.COMMAND:
whatis
DESCRIPTION:
display manual page descriptions
SYNOPSIS
whatis commandName
Example:
piniheaven@fish:~$ whatis firefox
firefox (1) - a free and open source web browser from Mozilla
piniheaven@fish:~$ whatis ls
ls (1) - list directory contents
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