To find last day of any month & year using unix command

How to keep track of your Unix/Linux command execution and its output

By using "script" command, you can keep track of Executed Commands and its output.

Definition: The script command will keep a transcript(written record) of everything you say to the computer and everything that the computer responds to you.

Syntax: script [capturefilename]

*) To start the script command
eg: vjsujay$ script cmdlog

Note: cmdlog will be created in the current dir and also if you are not specifying the filename means, it will create a default filename 'typescript'

*) To stop capturing or script command,
eg: vjsujay$ exit

Different ways of running a Shell Script

1. Executing the Shell Script file as a command in the Shell Prompt
vjsujay@linuxdemon$sample.sh

2. Executing the Shell Script file using specified Shell
vjsujay@linuxdemon$bash sample.sh

3. Executing the Shell Script file in the current Shell
vjsujay@linuxdemon$source sample.sh
or
vjsujay@linuxdemon$. sample.sh

4. Executing the Shell Script file using exec command
vjsujay@linuxdemon$ exec sample.sh

Copying longfilenames without retyping

$ ls -l thisismytestfile
-rw-r--r-- 1 Ajay None 13 Apr 17 03:22 thisismytestfile

Ajay@intel ~
$ cp thisismytestfile{,.bk}

Ajay@intel ~
$ ls -l thisismytest*
-rw-r--r-- 1 Ajay None 13 Apr 17 03:22 thisismytestfile
-rw-r--r-- 1 Ajay None 13 Apr 17 03:26 thisismytestfile.bk

How to Truncate a file in Unix/Linux

:>filename

If the filename already exists,the file will be truncated to ZERO byte file else a new file with ZERO byte will be created.

Example:

[vjsujay@phenix vjsujay]$ ls -l jsk
-rw-r----- 1 vjsujay free 46 Jun 25 20:14 jsk

[vjsujay@phenix vjsujay]$ : > jsk

[vjsujay@phenix vjsujay]$ ls -l jsk
-rw-r----- 1 vjsujay free 0 Jun 25 20:15 jsk

One more example with 3 different methods:

volcano@volcano-laptop:~/test/trunc$ ls -ltr
total 12
-rw-r--r-- 1 volcano volcano 14 2011-02-23 11:56 rado
-rw-r--r-- 1 volcano volcano 14 2011-02-23 11:57 radoo
-rw-r--r-- 1 volcano volcano 14 2011-02-23 11:57 radooo
volcano@volcano-laptop:~/test/trunc$ > rado
volcano@volcano-laptop:~/test/trunc$ :>radoo
volcano@volcano-laptop:~/test/trunc$ true > radooo
volcano@volcano-laptop:~/test/trunc$ ls -ltr
total 0
-rw-r--r-- 1 volcano volcano 0 2011-02-23 11:57 rado
-rw-r--r-- 1 volcano volcano 0 2011-02-23 11:57 radoo
-rw-r--r-- 1 volcano volcano 0 2011-02-23 11:57 radooo

Commenting Multiple lines in a shell script

By using anonymous here document, we can comment multiple lines in a shell script for debugging purposes.

eg:

: << COMMENT
echo "Not in the Scope of debugging/execution"
a=5
b=3
let c=a+b
echo $c
COMMENT

The statements in between the anonymous here document will not be executed.

Length of a string in Linux

The command syntax is ${#string}

Example:
linuxdemon$lindem="linux demon"
linuxdemon$echo ${#lindem}
11

Explanation:
1.Assigning the string linux demon to the variable lindem.
2.Determining and printing the length of the string.

FTP Automation using Shell script

I am going to give the code in shell script for ftp automation.

ftp -n servername/serverIP << FTP_AUTO
user giveusername givepassword

Any ftp command you can give here

bye
FTP_AUTO

Explanation:
1. -n is used to restrict the ftp from attempting auto login.
2. << here document concept applied here and hence the tag is FTP_AUTO
3. user is the ftp command
4. You can give any ftp command after the user command to do your job.
5.End the here document with the same tag FTP_AUTO

How to mount WIN partition in Linux?

Temporary Mounting: After the reboot of your system, you need to again execute the mount command to mount the win partition in Linux.

1.You need to create mount point(directory) for each win partition(drives) inside the /mnt directory.
eg: mkdir /mnt/winc (You can give any name instead of winc)

2. By using the mount command, we can now mount the windows partition
eg: mount -t vfat /dev/hda1 /mnt/winc (In linux, first partition is called as hda1)

3. Now get inside the /mnt/winc directory and check the files.You will be able to see your files from C drive.
eg: cd /mnt/winc

Permanent Mounting: To do the permanent mounting, you need to follow these steps below.

1.Create mount points (mkdir /mnt/winc)

2.Edit the /etc/fstab file using any text editor like vi and insert the mount point and file system details at the end of the file with the proper spacing as previous lines.
eg: /dev/hda1 /mnt/winc vfat

3. After the reboot of your system, you will be able to access all C drive files.

How to rename group of files?

I am giving a simple shell script, for renaming a group of files in the current directory.In the script, i have renamed all .jsk files to .txt files.

for filename in *.jsk
do
mv $filename `basename $filename jsk`txt
done

Explanation:
1.In the for statement, i am finding out all the .jsk extension files.
2.In the mv statement, i am using basename command to strip the jsk extension.