Linux Shell script BASICS (7)

Linux Shell script basics if you only look at the previous theoretical section, although there are some examples, but it is not systematic enough, here we will show you a specific example of Linux Shell script programming, to help you learn and improve the basics of Linux Shell.

Part 1 instances

Now let's discuss the general steps for writing a script. Any excellent script should have help and input parameters. And write a pseudo script (Framework. Sh) that contains the framework structure required by most scripts, which is a very good idea. At this time, when writing a new script, we only need to execute the Copy command:

CP framework. Sh myscript

Then insert your own function.

Let's look at another example:

Binary to decimal conversion

The script b2d converts the binary number (such as 1101) to the corresponding decimal number. This is also an example of a mathematical operation using the expr command:

#! /Bin/sh

# VIM: Set Sw = 4 ts = 4 et:

Help ()

{

Cat <

B2H -- convert binary to decimal

Usage: B2H [-H] binarynum

Options:-H help text

Example: B2H 111010

Will return 58

Help

Exit 0

}

Error ()

{

# Print an error and exit

Echo "$1"

Exit 1

}

Lastchar ()

{

# Return the last character of a string in $ rval

If [-z "$1"]; then

# Empty string

Rval = ""

Return

Fi

# WC puts some space behind the output this is why we need sed:

Numofchar = 'echo-n "$1" | WC-c | SED's // g''

# Now cut out the last char

Rval = 'echo-n "$1" | cut-B $ numofchar'

}

Chop ()

{

# Remove the last character in string and return it in $ rval

If [-z "$1"]; then

# Empty string

Rval = ""

Return

Fi

# WC puts some space behind the output this is why we need sed:

Numofchar = 'echo-n "$1" | WC-c | SED's // g''

If ["$ numofchar" = "1"]; then

# Only One char in string

Rval = ""

Return

Fi

Numofcharminus1 = 'expr $ numofchar "-" 1'

# Now cut all but the last CHAR:

Rval = 'echo-n "$1" | cut-B 0-$ {numofcharminus1 }'

}

While [-n "$1"]; do

Case $1 in

-H) Help; shift 1; # function help is called

--) Shift; break; # End of options

-*) Error "error: no such option $1.-H for help ";;

*) Break ;;

Esac

Done

# The main program

Sum = 0

Weight = 1

# One Arg must be given:

[-Z "$1"] & Help

Binnum = "$1"

Binnumorig = "$1"

While [-n "$ binnum"]; do

Lastchar "$ binnum"

If ["$ rval" = "1"]; then

Sum = 'expr "$ weight" "+" "$ sum "'

Fi

# Remove the last position in $ binnum

Chop "$ binnum"

Binnum = "$ rval"

Weight = 'expr "$ weight" "*" 2'

Done

Echo "binary $ binnumorig is decimal $ sum"

TheAlgorithmIt uses decimal and binary values (, 16,...). For example, binary "10" can be converted to decimal:

0*1 + 1*2 = 2

To obtain a single binary number, we use the lastchar function. This function uses WC-C to calculate the number of characters, and then uses the cut command to retrieve the last character. The Chop function removes the last character.

This Linux Shell script instance helps us complete the conversion. Next time we will give an example of a file loop Program .