Requirement-Driven Linux Shell Programming

• 1. Where can I find the basic Material about Linux Shell Programming?
• 2. How to time a function/program(Get the execution time of a program)?
• 3. How to pass parameters to a function?
• 4. How to calculate float point in Shell?
• 5. How to output nicer to the console, like a table?
• 6. How to print the destined(specific) line of a file?
• 7. How to covert column to row?
• 8. How to output a certain lines of a file?(Say, all but the first line)
• 9. How to list(copy) all the executable files in a directory?
• 10. The short key for adding source block in org mode:
• 11. How to remove the duplicated newlines in a file?
• 12. How to transpose a file(to convert all the colums to rows)?
• 13. How to 向上取整 an floating point number?

I found this tutorial useful,A Beginner‘s Handbook for Linux Shell Scripting. There are many places you can find such materials, and you can take a quick look at it whenever you are in need.

Command Format: time the_program_to_be_tested
Note:the output of "time" command will be the STDERR_FILENO,in my case, I want to redirect the output to a file, so the following command is used:

Suppose the following code section:

1: time_xtar_load()
2: {
3:     time ./xtar_load $1
4: }
5: 
6: for ((i = 0;i < $num_process;i++))
7: do
8:     time_xtar_load $i &
9: done

In this example, a function named time_xtar_load is defined, and the "for" statement will evoke the function many times each with a different parameter, that is, the running value of i.

The default behavior of the shell to the calculation works is limited to integers, the tool "bc" is needed to do more advanced calculations.for example:

1: while read MINUTE SECOND
2: do
3:     total=`echo "$MINUTE * 60 + $SECOND" | bc`
4:     sum=`echo "$total + $sum" | bc`
5: done < ctar_load_sys
6: 
7: avg=`echo "scale=10;$sum / $n" | bc`

In the above code segment, two self-defined variables(MINUTE, SECOND) are read from a file named "ctar_load_sys", they are used to get the total number in seconds, and after the while terminates, the average time is calculated with the last line of code.Note that the "scale=10" is necessary to do the decimal computation.

The "printf" command can do exactly what we can do in C/C++, it has rich formats to choose from. For example:

1: header="\n %-10s %10s %10s\n"
2: format=" %-10s %10.3f %10.3f\n"
3: printf "$header" " " "sum" "avg"
4: printf "$format" 5: real $sum $avg    6: sys  $sum $avg

The above code prints a table on the console as follows:

Use the following command:

Say, I have a file(nofs) which has the following contents:

nofs 30.049 57.857 115.718

and I want to covert it to one row, there are many ways to do it:

1.The awk way:

2.The tr way:

3.The echo:

All of the above methods will output like:

will output the file contents from the second line.

List:

1: find . -executable -type f

Copy:

1: find . -executable -type f | xargs -i cp {} /tmp

I get a file with the following format:

write rewrite read re-read randread randwrite

32149.29 35625.84 37261.05 37575.87 713.54 1606.12

57465.48 62242.62 66024.14 66969.32 1430.75 3365.54

89339.57 96388.80 104037.65 103917.83 2714.76 6479.37

128849.01 132933.47 133952.92 134381.05 5482.03 12207.46

126489.87 128470.04 129826.87 130348.56 10446.49 24424.78

127078.48 128236.06 128642.23 129169.20 19505.88 40367.71

126942.59 125676.09 128773.13 128896.08 32061.20 63187.50

127596.32 128102.95 128516.09 129485.38 51048.20 82756.15

126424.50 127839.95 128780.78 129846.62 72924.07 97219.43

125817.65 127208.07 128134.88 129057.43 92172.60 85037.41

128768.69 129389.45 130342.52 131162.48 107949.98 100109.50

127326.84 128567.19 129666.99 129796.52 117193.84 108822.87

And I just want to remove all the empty lines of the file, the following command can be used:

or

The command will output the following result:

Use the following script:

 1:   transpose_file()
 2: {
 3: 	lines_of_file=`wc -l < "$1"`
 4: 	echo $lines_of_file
 5: 	result_file_name="result"
 6: 	>$result_file_name
 7: 
 8: 	for ((line_index = 1;line_index < $lines_of_file + 1;line_index++))
 9: 	do
10: 		sed -n ${line_index}p "$1" | tr ‘ ‘ ‘\n‘ | awk ‘$1‘ > /tmp/a
11: 		paste $result_file_name /tmp/a > /tmp/b
12: 		cp /tmp/b $result_file_name
13: 	done
14: }

Using the following command: