Awk基本入门[6] Additional Awk Commands 1
1、Pretty Printing Using printf
Syntax:
printf "print format", variable1, variable2, etc.
Special Characters in the printf Format
The following prints "Line 1" and "Line 2" in separate lines using newline:
$ awk 'BEGIN { printf "Line 1\nLine 2\n" }' Line 1 Line 2
The following prints different fields separated by tabs, with 2 tabs after "Field 1":
$ awk 'BEGIN \ { printf "Field 1\t\tField 2\tField 3\tField 4\n" }'
Field 1 Field 2 Field 3 Field 4
The following prints vertical tabs after every field:
$ awk 'BEGIN { printf "Field 1\vField 2\vField 3\vField 4\n" }' Field 1 Field 2 Field 3 Field 4
The following prints a backspace after every field except Field4. This erases the last number in each of the first three fields.
$ awk 'BEGIN \ { printf "Field 1\bField 2\bField 3\bField 4\n" }' Field Field Field Field 4
In the following example, after printing every field, we do a "Carriage Return" and print the next value on top of the current printed value.
$ awk 'BEGIN \ { printf "Field 1\rField 2\rField 3\rField 4\n" }' Field 4
Printf Format Specifiers
The following example shows the basic usage of the format specifiers:
$ cat printf-format.awk BEGIN { printf "s--> %s\n", "String" printf "c--> %c\n", "String" printf "s--> %s\n", 101.23 printf "d--> %d\n", 101.23 printf "e--> %e\n", 101.23 printf "f--> %f\n", 101.23 printf "g--> %g\n", 101.23 printf "o--> %o\n", 0x8 printf "x--> %x\n", 16 printf "percentage--> %%\n", 17 } $ awk -f printf-format.awk s--> String c--> S s--> 101.23 d--> 101 e--> 1.012300e+02 f--> 101.230000 g--> 101.23 o--> 10 x--> 10 percentage--> %
Print with Fixed Column Width (Basic)
To create a fixed column width report, you have to specify a number immediately after the % in the format specifier. This number indicates the minimum number of character to be printed. When the input-string is smaller than the specified number, spaces are added to the left to make it fixed width.
Spaces are added to the left to print “Good” as a 6 character string:
$ awk 'BEGIN { printf "|%6s|\n", "Good" }' | Good|
The whole string is printed here even though you specified 6 character width:
$awk 'BEGIN { printf "|%6s|\n", "Good Boy!" }' |Good Boy!|
Print with Fixed Width (Left Justified)
When the input-string is less than the number of characters specified, and you would like it to be left justified (by adding spaces to the right), use a minus symbol (-) immediately after the % and before the number.
"%-6s" is left justified as shown below:
$ awk 'BEGIN { printf "|%-6s|\n", "Good" }' |Good |
Print with Leading Zeros
For right justified with 0's in front of the number (instead of the space), add a zero (0) before the number. i.e. Instead of "%5s", use "%05s" as the format identifier.
$ awk 'BEGIN { printf "|%05s|\n", "100" }' |00100|
Print Absolute Fixed Width String Value
To print maximum of ONLY 6 characters, add a decimal before the number. i.e. Instead of "%6s", give "%.6s", which will print only 6 characters from the input string, even when the input string is longer than that as shown below.
$ awk 'BEGIN { printf "%.6s\n", "Good Boy!" }' Good B
Dot . Precision
A dot before the number in format identifier indicates the precision.
This example shows how the number "101.23" is printed differently when using using .1 and .4 (using d, e, f, and g format specifier).
$ cat dot.awk BEGIN { print "----Using .1----" printf ".1d--> %.1d\n", 101.23 printf ".1e--> %.1e\n", 101.23 printf ".1f--> %.1f\n", 101.23 printf ".1g--> %.1g\n", 101.23 print "----Using .4----" printf ".4d--> %.4d\n", 101.23 printf ".4e--> %.4e\n", 101.23 printf ".4f--> %.4f\n", 101.23 printf ".4g--> %.4g\n", 101.23 } $ awk -f dot.awk ----Using .1---- .1d--> 101 .1e--> 1.0e+02 .1f--> 101.2 .1g--> 1e+02 ----Using .4---- .4d--> 0101 .4e--> 1.0123e+02 .4f--> 101.2300 .4g--> 101.2
Print Report to File
You can redirect the output of a print statement to a specific output file inside the awk script. In the following example the 1st print statement has "> report.txt", which creates the report.txt file and sends the output of the prints statement to it. All the subsequent
print statements have ">> report.txt", which appends the output to the existing report.txt file.
$ cat printf-width4.awk BEGIN { FS="," printf "%-3s\t%-10s\t%-10s\t%-5s\t%-3s\n", "Num","Description","Type","Price","Qty" > "report.txt" printf "-----------------------------------------------------\ n" >> "report.txt" } { if ($5 > 10) printf "%-3d\t%-10s\t%-10s\t$%-.2f\t%03d\n", $1,$2,$3,$4,$5 >> "report.txt" } $ awk -f printf-width4.awk items.txt $ cat report.txt Num Description Type Price Qty ------------------------------------------------- 103 MP3 Player Audio 104 $270.00 015 Tennis Racket Sports $190.00 020
2、Built-in Numeric Functions
Awk int(n) Function
n is any number with or
with out floating point. If you give a whole number as an argument, this function returns the same number; for a floating point number, it truncates.
Init Function Example:
$ awk 'BEGIN{ print int(3.534); print int(4); print int(-5.223); print int(-5); }'
3
4
-5
-5
The above command produces the following output.
Awk log(n) Function
The log(n) function provides the natural logarithm of given argument n. The number n must be positive, or an error will be thrown.
Awk sqrt(n) Function
sqrt function gives the positive square root for the given integer n.This function also requires a positive number, and it returns nan error if you give the negative number as an argument.
Awk exp(n) Function
The exp(n) function provides e to the power of n.
Awk sin(n) Function
The sin(n) function gives the sine of n, with n in radians.
Awk cos(n) Function
The cos(n) returns the cosine of n, with n in radians.
Awk atan2(m,n) Function
This function gives you the arc-tangent of m/n in radians.
3、Random Number Generator
Awk rand() Function
rand() is used to generate a random number between 0 and 1. It never returns 0 or 1, always a value between 0 and 1. Numbers are random within one awk run, but predictable from run to run.
The following example generates 1000 random numbers between 0 and 100, and shows how often each number was generated.
$ cat rand.awk BEGIN { while(i<1000) { n = int(rand()*100); rnd[n]++; i++; } for(i=0;i<=100;i++) { print i,"Occured", rnd[i], "times"; } } $ awk -f rand.awk 0 Occured 6 times 1 Occured 16 times 2 Occured 12 times 3 Occured 6 times 4 Occured 13 times 5 Occured 13 times 6 Occured 8 times 7 Occured 7 times 8 Occured 16 times 9 Occured 9 times 10 Occured 6 times 11 Occured 9 times 12 Occured 17 times 13 Occured 12 times
From the above output, we can see that the rand() function can generate repeatable numbers very often.
Awk srand(n) Function
srand(n) is used to initialize the random number generation with a given argument n. Whenever program execution starts, awk starts generating its random numbers from n. If no argument were given, awk would use the time of the day to generate the seed.
