September 2012 | Linux Blog

Perl Script: Convert any given string To-Lower or To-Upper case

Below is simple perl script which converts any given string to Upper or to-Lower case ...
Here, we have used the perl Escape Sequence ( \U \L \E)

\U -- Convert all following letters to Uppercase
\L -- Convert all following letters to Lowercase
\E -- Ends the effect of \L, \U or \Q

Feel free to copy and use this code ...

Source: cat case-conversion.pl
#!/usr/bin/perl

print "Enter the string: ";
$var = <STDIN>;

print "To uppercase: \U${var}\E \n";
print "To lowercase: \L${var}\E \n";

Output: perl case-conversion.pl
Enter the string: LinuxPoison
To uppercase: LINUXPOISON
To lowercase: linuxpoison

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Bash Script: Script to check internet connection

Below is simple bash script to test the Internet connection using wget utility.
Feel free to copy and use this script

Source: cat internet_connection.sh
#!/bin/bash

HOST=$1
WGET="/usr/bin/wget"

$WGET -q --tries=10 --timeout=5 $HOST
RESULT=$?

if [[ $RESULT -eq 0 ]]; then
echo "Connection made successfully to $HOST"
else
echo "Fail to make connection to $HOST"
fi

Output:
./internet_connection.sh http://yahoo.com
Connection made successfully to http://yahoo.com

./internet_connection.sh http://yahosssss.com
Fail to make connection to http://yahosssss.com

Bash Script: Commenting out the block of code using here document

Many times it required to comment out the huge block of code for debugging purpose and it is very annoying to put the "#" tag before each and every line of this code

Below shell script shows how to comment out the block of code using here document (: <<'COMMENT')

Source: cat comment_block.sh
#!/bin/bash

echo "statement before comment."
: <<'COMMENT'
echo "This is inside the comment block and will not get printed"
a=0
b=20
echo $((b/a))
echo "No error"
COMMENT

echo "This is after the comment block."
exit

Output: ./comment_block.sh
statement before comment.
This is after the comment block.

Bash Script: Transfer files through FTP from within script

Below shell script demonstrate the usage of FTP operation from within the bash script, feel free to copy and use this script:

Source: cat autoftp.sh
#!/bin/bash

if [ $# -ne 1 ]; then
echo "Please provide the file path for ftp operation."
exit
fi

USERNAME=linuxpoison
PASSWORD=password
FILENAME="$1"
FTP_SERVER=ftp.foo.com
echo "Starting the ftp operation ...."

ftp -n $FTP_SERVER <<Done-ftp
user $USERNAME $PASSWORD
binary
put "$FILENAME"
bye
Done-ftp

echo "Done with the transfer of file: $FILENAME"
exit

Output: ./autoftp.sh log.tar.gz
Starting the ftp operation ....
Done with the transfer of file: log.tar.gz

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Bash Script: Convert File from DOS to UNIX format

Common problem! If you need to exchange text files between DOS/Windows and Linux, be aware of the "end of line" problem. Under DOS, each line of text ends with CR/LF (Carriage return/Line feed), with LF under Linux. If you edit a DOS text file under Linux, each line will likely end with a strange--looking `M' character;

Below is simple shell script which converts the files in DOS format to Unix format
Feel free to copy and use this code

Source: cat dos_unix.sh
#!/bin/bash

if [ $# -ne 1 ]; then
        echo "Please provide the path of a valid DOS file"
        exit
fi

if [ ! -f "$1" ]; then
        echo "Cannot access file: $1"
        echo "Don't play, provide the vaild file."
        exit
fi

DOSFILE=$1
UNIXFILE=output.unix
CR='\015'

tr -d $CR < $DOSFILE > $UNIXFILE

echo "Done with the conversion"
echo "New output file is: $UNIXFILE"
exit

Bash Script: Get the Information about the caller of the function (backtrace)

Caller Returns the context of any active subroutine call (a shell function or a script executed with the . or source builtins). caller displays the line number and source filename of the current subroutine call. If a non-negative integer is supplied as expr, caller displays the line number, subroutine name, and source file corresponding to that position in the current execution call stack. This extra information may be used, for example, to print a stack trace.

Below is simple bash script which demonstrate the usage of caller ...
feel free to copy and use this code

Source: cat caller.sh
#!/bin/bash

foo() {
        caller 0
        echo "In function: foo"
}

echo "Outside of the function"

goo() {
        echo "In function: goo"
        foo
}

goo

Output: ./caller.sh
Outside of the function
In function: goo
13 goo ./caller.sh
In function: foo

Bash Script: Write debugging information to /var/log/messages

logger is a shell command interface to the syslog system log module, it appends a user-generated message to the system log (/var/log/messages). You do not have to be root to invoke logger.

Below is the simple bash script to log the debugging information to /var/log/message
Feel free to copy and use the below code

Source: cat logger.sh
#!/bin/bash

echo -n "Enter your username: "
read username

logger -i "Username $username started the script"

echo -n "Enter your Password: "
read password

# This is just an sample for comparing the password
if [ "$password" = "linuxpoison" ]; then
        echo "welcome $username"
        logger -i "Authentication successful for $username."
else
        echo "your Username or password does not match"
        logger -i "Authentication failed for $username."
fi

Bash Script: Set the timeout for reading the user input

If TMOUT set to a value greater than zero, TMOUT is treated as the default timeout for the read builtin. The select command terminates if input does not arrive after TMOUT seconds when input is coming from a terminal.

In an interactive shell, the value is interpreted as the number of seconds to wait for input after issuing the primary prompt. Bash terminates after waiting for that number of seconds if input does not arrive.

Below is the bash script which explains the above concept ...
Feel free to copy and use this script

Source: cat timeout.sh
#!/bin/bash

TMOUT=5
echo -n "Enter you username: "
read username

if [[ -z $username ]]; then
        # No username provide
        username="Not Set"
        echo "Timeout, Run this script again and set your valid username..."
fi

Output: ./timeout.sh
Enter you username: Timeout, Run this script again and set your valid username...

Bash Script: Running part of the script in restricted mode

If Bash is started with the name rbash, or the --restricted or -r option is supplied at invocation, the shell becomes restricted. A restricted shell is used to set up an environment more controlled than the standard shell. A restricted shell behaves identically to bash with the exception that the following are disallowed or not performed:

* Changing directories with the cd built-in.
* Setting or unsetting the values of the SHELL, PATH, ENV, or BASH_ENV variables.
* Specifying command names containing slashes.
* Specifying a filename containing a slash as an argument to the . built-in command.
* Specifying a filename containing a slash as an argument to the -p option to the hash built-in command.
* Importing function definitions from the shell environment at startup.
* Parsing the value of SHELLOPTS from the shell environment at startup.
* Redirecting output using the ‘>’, ‘>|’, ‘<>’, ‘>&’, ‘&>’, and ‘>>’ redirection operators.
* Using the exec built-in to replace the shell with another command.
* Adding or deleting built-in commands with the -f and -d options to the enable built-in.
* Using the enable built-in command to enable disabled shell built-ins.
* Specifying the -p option to the command built-in.

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