Example
General programming step
Now let's discuss the general steps to write a script. Any excellent script should have help and input parameters. And write a fake script (framework.sh), which contains the framework structure that most scripts need, is a very good idea. At this time, we only need to execute the copy command when writing a new script:
CP Framework.sh Myscript
Then insert your own function.
Let us look at two examples:
Binary to decimal conversion
The script B2D converts the binary number (such as 1101) into the corresponding decimal number. This is also an example of mathematical operation with an expr command:
#! / bin / sh
# vim: set sw = 4 TS = 4 et:
Help ()
{
Cat << Help
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 $ RAL
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 $ RALAL
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 ;;
Esacdone
# 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"
#
The algorithm used by this script is to use decimal and binary value (1, 2, 4, 8, 16, ..), such as binary "10" can be converted into Ten-based:
0 * 1 1 * 2 = 2
In order to get a single binary number, we use the lastchar function. This function uses the WC-C calculating the number of characters and then uses the CUT command to take out a character. The function of the CHOP function is to remove the last character.
File cycle program
Perhaps you want to save all sent messages to one of the people in a file, but after a few months, this file may become great to make the accesses for the file slow down. The following script RotateFile can solve this problem. This script can rename the mail save file (assuming to Outmail) is Outmail.1, and it has become Outmail.2, etc. for Outmail.1, etc. ...
#! / bin / sh
# vim: set sw = 4 TS = 4 et:
Ver = "0.1"
Help ()
{
Cat << Help
RotateFile - Rotate the file name
USAGE: ROTATEFILE [-H] FileName
Options: -h Help Text
Example: RotateFile Out
This Will E.G Rename Out.2 to out.3, out to out.2, out to out.1
AND CREATE AN EMPTY OUT-FILE
THE MAX NUMBER IS 10
Version $ VER
Help
EXIT 0
}
Error ()
{
Echo "$ 1"
EXIT 1
}
While [-n "$ 1"]; do
Case $ 1 in
-H) HELP; Shift 1 ;;
-) BREAK ;;
- *) Echo "Error: No Such Option $ 1. -h for help"; exit 1 ;;
*) BREAK ;;
ESAC
DONE
# input check:
IF [-z "$ 1"]; then
Error "error: you must specify a file, use -h for help"
Fi
FILEN = "$ 1"
# Rename Any .1, .2 etc file:
For N in 9 8 7 6 5 4 3 2 1; DoiF [-f "$ filen. $ n"]; then
P = `EXPR $ N 1`
Echo "MV $ Filen. $ n $ filen. $ p"
MV $ Filen. $ N $ filen. $ p
Fi
DONE
# Rename The Original File:
IF [-f "$ filen"]; then
Echo "MV $ Filen $ Filen.1"
MV $ Filen $ Filen.1
Fi
Echo Touch $ Filen
Touch $ Filen
How is this script work? After the user provides a file name, we will perform a cycle of 9 to 1. The file 9 is named 10, and the file 8 is renamed 9 and so on. After the loop is complete, we name the original file to file 1 to establish a empty file with the same name as the original file.
debugging
The easiest debug command is of course using an echo command. You can print any variable values using Echo in any place where you doubt. This is also the cause of 80% of the time to debug the procedure. The advantage of the shell program does not need to recompile, and insert an echo command does not need much time.
The shell also has a real debug mode. If there is an error in the script "STRANGEScript", you can debug this:
SH -X StrangeScript
This will execute the script and display the value of all variables.
There is still a mode that doesn't need to perform scripts just check the syntax. It can be used like this:
sh -n your_script
This will return all syntax errors.
We hope that you can start writing your own shell script, I hope you have fun.
