Linux Sysadmin
AWK: The Linux Administrators' Wisdom Kit
By Emmett Dulaney
Learning Linux? This introduction to the invaluable AWK text-manipulation tool will be invaluable.
The AWK utility, with its own self-contained
language, is one of the most powerful data processing engines in
existence — not only in Linux, but anywhere. The limits to what can be
done with this programming and data-manipulation language (named for
the last initials of its creators, Alfred Aho, Peter Weinberger, and
Brian Kernighan) are the boundaries of one's own knowledge. It allows
you to create short programs that read input files, sort data, process
it, perform arithmetic on the input, and generate reports, among myriad
other functions.
What Is AWK?
To put it the simplest way possible, AWK is a
programming-language tool used to manipulate text. The language of the
AWK utility resembles the shell-programming language in many areas,
although AWK's syntax is very much its own. When first created, AWK was
designed to work in the text-processing arena, and the language is
based on executing a series of instructions whenever a pattern is
matched in the input data. The utility scans each line of a file,
looking for patterns that match those given on the command line. If a
match is found, it takes the next programming step. If no match is
found, it then proceeds to the next line.
While the operations can get complex, the syntax for the command is always:
awk '{pattern + action}' {filenames}
where pattern
represents what AWK is looking for in the data, and action is a series
of commands executed when a match is found. Curly brackets ({}) are not
always required around your program, but they are used to group a
series of instructions based on a specific pattern.
Understanding Fields
The utility separates each input line into records and fields. A record
is a single line of input, and each record consists of several fields.
The default-field separator is a space or a tab, and the record
separator is a new line. Although both tabs and spaces are perceived as
field separators by default (multiple blank spaces still count as one
delimiter), the delimiter can be changed from white space to any other
character.
To illustrate, look at the following employee-list file saved as emp_names:
46012 DULANEY EVAN MOBILE AL
46013 DURHAM JEFF MOBILE AL
46015 STEEN BILL MOBILE AL
46017 FELDMAN EVAN MOBILE AL
46018 SWIM STEVE UNKNOWN AL
46019 BOGUE ROBERT PHOENIX AR
46021 JUNE MICAH PHOENIX AR
46022 KANE SHERYL UNKNOWN AR
46024 WOOD WILLIAM MUNCIE IN
46026 FERGUS SARAH MUNCIE IN
46027 BUCK SARAH MUNCIE IN
46029 TUTTLE BOB MUNCIE IN
As AWK reads the input, the entire record is assigned to the variable $0. Each field, as split with the field separator, is assigned to the variables $1, $2, $3,
and so on. A line contains essentially an unlimited number of fields,
with each field being accessed by the field number. Thus, the command
awk '{print $1,$2,$3,$4,$5}' names
would result in a printout of
46012 DULANEY EVAN MOBILE AL
46013 DURHAM JEFF MOBILE AL
46015 STEEN BILL MOBILE AL
46017 FELDMAN EVAN MOBILE AL
46018 SWIM STEVE UNKNOWN AL
46019 BOGUE ROBERT PHOENIX AR
46021 JUNE MICAH PHOENIX AR
46022 KANE SHERYL UNKNOWN AR
46024 WOOD WILLIAM MUNCIE IN
46026 FERGUS SARAH MUNCIE IN
46027 BUCK SARAH MUNCIE IN
46029 TUTTLE BOB MUNCIE IN
An important item of noteworthiness is that AWK
interprets the five fields as being separated by white space, but when
it prints the display, there is only one space between each field. By
virtue of the ability to address each field with a unique number, you
can choose to print only certain fields. For example, to print only the
names from each record, select only the second and third fields to
print:
$ awk '{print $2,$3}' emp_names
DULANEY EVAN
DURHAM JEFF
STEEN BILL
FELDMAN EVAN
SWIM STEVE
BOGUE ROBERT
JUNE MICAH
KANE SHERYL
WOOD WILLIAM
FERGUS SARAH
BUCK SARAH
TUTTLE BOB
$
You can also specify that the fields print in
any order, regardless of how they exist in the record. Thus, to show
only the name fields, and reverse them so the first name is shown, then
the last:
$ awk '{print $3,$2}' emp_names
EVAN DULANEY
JEFF DURHAM
BILL STEEN
EVAN FELDMAN
STEVE SWIM
ROBERT BOGUE
MICAH JUNE
SHERYL KANE
WILLIAM WOOD
SARAH FERGUS
SARAH BUCK
BOB TUTTLE
$
Working with Patterns
You can select the action to take place only on
certain records, and not on all records, by including a pattern that
must be matched. The simplest form of pattern matching is that of a
search, wherein the item to be matched is included in slashes (/pattern/). For example, to perform the earlier action only on those employees who live in Alabama:
$ awk '/AL/ {print $3,$2}' emp_names
EVAN DULANEY
JEFF DURHAM
BILL STEEN
EVAN FELDMAN
STEVE SWIM
$
If you do not specify what fields to print, the entire matching entry will print:
$ awk '/AL/' emp_names
46012 DULANEY EVAN MOBILE AL
46013 DURHAM JEFF MOBILE AL
46015 STEEN BILL MOBILE AL
46017 FELDMAN EVAN MOBILE AL
46018 SWIM STEVE UNKNOWN AL
$
Multiple commands for the same set of data can be separated with a semicolon (;). For example, to print names on one line and city and state on another:
$ awk '/AL/ {print $3,$2 ; print $4,$5}' emp_names
EVAN DULANEY
MOBILE AL
JEFF DURHAM
MOBILE AL
BILL STEEN
MOBILE AL
EVAN FELDMAN
MOBILE AL
STEVE SWIM
UNKNOWN AL
$
If the semicolon were not used (print $3,$2,$4,$5),
all would appear on the same line. On the other hand, if the two print
statements were given separately, an altogether different result would
occur:
$ awk '/AL/ {print $3,$2} {print $4,$5}' emp_names
EVAN DULANEY
MOBILE AL
JEFF DURHAM
MOBILE AL
BILL STEEN
MOBILE AL
EVAN FELDMAN
MOBILE AL
STEVE SWIM
UNKNOWN AL
PHOENIX AR
PHOENIX AR
UNKNOWN AR
MUNCIE IN
MUNCIE IN
MUNCIE IN
MUNCIE IN
$
Fields three and two are given only when AL
is found in the listing. Fields four and five, however, are
unconditional and always print. Only the commands within the first set
of curly braces are active for the command (/AL/) immediately preceding.
The result is altogether cumbersome to read and
can use cleaning up a bit. First, insert a space and comma between city
and state. Next, leave a blank line after each two-line display:
$ awk '/AL/ {print $3,$2 ; print $4", "$5"\n"}' emp_names
EVAN DULANEY
MOBILE, AL
JEFF DURHAM
MOBILE, AL
BILL STEEN
MOBILE, AL
EVAN FELDMAN
MOBILE, AL
STEVE SWIM
UNKNOWN, AL
$
Between the fourth and fifth fields, a comma and
a space are added (between the quotation marks), and after the fifth
field, a new line character (\n) is printed. All the special characters that can be used with the echo command can be also be used with AWK print statements, including:
- \n (new line)
- \t (tab)
- \b (backspace)
- \f (formfeed)
- \r (carriage return)
Thus, to read all five fields, which were originally separated by tabs, and print them with tabs as well, you could program
$ awk '{print $1"\t"$2"\t"$3"\t"$4"\t"$5}' emp_names
46012 DULANEY EVAN MOBILE AL
46013 DURHAM JEFF MOBILE AL
46015 STEEN BILL MOBILE AL
46017 FELDMAN EVAN MOBILE AL
46018 SWIM STEVE UNKNOWN AL
46019 BOGUE ROBERT PHOENIX AR
46021 JUNE MICAH PHOENIX AR
46022 KANE SHERYL UNKNOWN AR
46024 WOOD WILLIAM MUNCIE IN
46026 FERGUS SARAH MUNCIE IN
46027 BUCK SARAH MUNCIE IN
46029 TUTTLE BOB MUNCIE IN
$
You can search for more than one pattern match
at a time by placing the multiple criteria in consecutive order and
separating them with a pipe (|) symbol:
$ awk '/AL|IN/' emp_names
46012 DULANEY EVAN MOBILE AL
46013 DURHAM JEFF MOBILE AL
46015 STEEN BILL MOBILE AL
46017 FELDMAN EVAN MOBILE AL
46018 SWIM STEVE UNKNOWN AL
46024 WOOD WILLIAM MUNCIE IN
46026 FERGUS SARAH MUNCIE IN
46027 BUCK SARAH MUNCIE IN
46029 TUTTLE BOB MUNCIE IN
$
This finds every match for Alabama and Indiana
residents. A problem occurs, however, when you try to find the people
who live in Arizona:
$ awk '/AR/' emp_names
46019 BOGUE ROBERT PHOENIX AR
46021 JUNE MICAH PHOENIX AR
46022 KANE SHERYL UNKNOWN AR
46026 FERGUS SARAH MUNCIE IN
46027 BUCK SARAH MUNCIE IN
$
Employees 46026 and 46027 do not live in
Arizona; however, their first names contain the character sequence
being searched for. The important thing to remember is that when
pattern matching in AWK, as in grep, sed,
or most other Linux/Unix commands, look for a match anywhere in the
record (line) unless told to do otherwise. To solve this problem, it is
necessary to tie the search to a particular field. This goal is
accomplished by means of a tilde (˜) and a specification to a specific
field, as the following example illustrates:
$ awk '$5 ˜ /AR/' emp_names
46019 BOGUE ROBERT PHOENIX AR
46021 JUNE MICAH PHOENIX AR
46022 KANE SHERYL UNKNOWN AR
$
The opposite of the tilde (signifying a match)
is a tilde preceded by an exclamation mark (!˜). These characters tell
the program to find all lines matching the search sequence, providing
the sequence does not appear in the specified field:
$ awk '$5 !˜ /AR/' names
46012 DULANEY EVAN MOBILE AL
46013 DURHAM JEFF MOBILE AL
46015 STEEN BILL MOBILE AL
46017 FELDMAN EVAN MOBILE AL
46018 SWIM STEVE UNKNOWN AL
46024 WOOD WILLIAM MUNCIE IN
46026 FERGUS SARAH MUNCIE IN
46027 BUCK SARAH MUNCIE IN
46029 TUTTLE BOB MUNCIE IN
$
In this case, it displayed all lines that do not
have AR in the fifth field including the two Sarah's entries that do
have AR, but in the third field instead of the fifth one.
Braces and Field Separators
The bracket characters play an important part in
the AWK commands. The actions that appear between them spell out what
will take place and when it will take place. When only one set of
brackets is used:
{print $3,$2}
all the actions between occur at the same time. When more than one set of brackets is used:
{print $3}{print $2}
the first sequence of commands is carried out
until completion, then the second sequence kicks in. Notice the
difference between the two listings that follow:
$ awk '{print $3,$2}' names
EVAN DULANEY
JEFF DURHAM
BILL STEEN
EVAN FELDMAN
STEVE SWIM
ROBERT BOGUE
MICAH JUNE
SHERYL KANE
WILLIAM WOOD
SARAH FERGUS
SARAH BUCK
BOB TUTTLE
$
$ awk '{print $3}{print $2}' names
EVAN
DULANEY
JEFF
DURHAM
BILL
STEEN
EVAN
FELDMAN
STEVE
SWIM
ROBERT
BOGUE
MICAH
JUNE
SHERYL
KANE
WILLIAM
WOOD
SARAH
FERGUS
SARAH
BUCK
BOB
TUTTLE
$
To reiterate the findings with multiple sets of
brackets, the commands within the first set are carried out until
completion; processing then moves to the second set. If there were a
third set, it would go to that set on completion of the second set, and
so on. In the generated printout, there are two separate print
commands, so the first one is carried out, followed by the second,
causing the display for each entry to appear on two lines instead of
one.
The field separator differentiating one field
from another need not always be white space; it can be any discernible
character. To illustrate, assume the emp_names file separated the fields with colons instead of tabs:
$ cat emp_names
46012:DULANEY:EVAN:MOBILE:AL
46013:DURHAM:JEFF:MOBILE:AL
46015:STEEN:BILL:MOBILE:AL
46017:FELDMAN:EVAN:MOBILE:AL
46018:SWIM:STEVE:UNKNOWN:AL
46019:BOGUE:ROBERT:PHOENIX:AR
46021:JUNE:MICAH:PHOENIX:AR
46022:KANE:SHERYL:UNKNOWN:AR
46024:WOOD:WILLIAM:MUNCIE:IN
46026:FERGUS:SARAH:MUNCIE:IN
46027:BUCK:SARAH:MUNCIE:IN
46029:TUTTLE:BOB:MUNCIE:IN
$
If you attempted to print the last name by specifying that you wanted the second field with
$ awk '{print $2}' emp_names
you would end up with twelve blank lines.
Because there are no spaces in the file, there are no discernible
fields beyond the first one. To solve the problem, AWK must be told
that a character other than white space is the delimiter, and there are
two methods by which to inform AWK of the new field separator: Use the
command-line parameter -F, or
specify the variable FS within the program. Both strategies work
equally well, with one exception, as illustrated by the following
example:
$ awk '{FS=":"}{print $2}' emp_names
DURHAM
STEEN
FELDMAN
SWIM
BOGUE
JUNE
KANE
WOOD
FERGUS
BUCK
TUTTLE
$
$ awk -F: '{print $2}' emp_names
DULANEY
DURHAM
STEEN
FELDMAN
SWIM
BOGUE
JUNE
KANE
WOOD
FERGUS
BUCK
TUTTLE
$
In the first command, a blank line is
incorrectly returned for the very first record, while all the others
work as they should. It is not until the second record is read that the
field separator is recognized and properly acted on. This shortcoming
can be corrected by using a BEGIN statement (more on that later). The -F works much like a BEGIN and is able to correctly read the first record and act on it as it should.
As I mentioned at the start of this article, the
default display/output field separator is a blank space. This feature
can be changed within the program by using the Output Field Separator (OFS) variable. For example, to read the file (separated by colons) and display it with dashes, the command would be
$ awk -F":" '{OFS="-"}{print $1,$2,$3,$4,$5}' emp_names
46012-DULANEY-EVAN-MOBILE-AL
46013-DURHAM-JEFF-MOBILE-AL
46015-STEEN-BILL-MOBILE-AL
46017-FELDMAN-EVAN-MOBILE-AL
46018-SWIM-STEVE-UNKNOWN-AL
46019-BOGUE-ROBERT-PHOENIX-AZ
46021-JUNE-MICAH-PHOENIX-AZ
46022-KANE-SHERYL-UNKNOWN-AR
46024-WOOD-WILLIAM-MUNCIE-IN
46026-FERGUS-SARAH-MUNCIE-IN
46027-BUCK-SARAH-MUNCIE-IN
46029-TUTTLE-BOB-MUNCIE-IN
$
FS and OFS,
(input) Field Separator and Output Field Separator, are but a couple of
the variables that can be used within the AWK utility. For example, to
number each line as it is printed, use the NR variable in the following manner:
$ awk -F":" '{print NR,$1,$2,$3}' emp_names
1 46012 DULANEY EVAN
2 46013 DURHAM JEFF
3 46015 STEEN BILL
4 46017 FELDMAN EVAN
5 46018 SWIM STEVE
6 46019 BOGUE ROBERT
7 46021 JUNE MICAH
8 46022 KANE SHERYL
9 46024 WOOD WILLIAM
10 46026 FERGUS SARAH
11 46027 BUCK SARAH
12 46029 TUTTLE BOB
$
To find all lines with employee numbers between 46012 and 46015:
$ awk -F":" '/4601[2-5]/' emp_names
46012 DULANEY EVAN MOBILE AL
46013 DURHAM JEFF MOBILE AL
46015 STEEN BILL MOBILE AL
$
Adding Text
Text may be added to the display in the same
manner as control sequences or other characters are. For example, to
change the delimiter from spaces to colons, the command could be
awk '{print $1":"$2":"$3":"$4":"$5}' emp_names > new_emp_names
In this case, the character (:), enclosed in quotation marks ("/"),
is added between each of the fields. This value within the quotation
marks can be anything. For example, to create a database-like display
of the employees living in Alabama:
$ awk '$5 ~ /AL/ {print "NAME: "$2", "$3"\nCITY-STATE:
"$4", "$5"\n"}' emp_names
NAME: DULANEY, EVAN
CITY-STATE: MOBILE, AL
NAME: DURHAM, JEFF
CITY-STATE: MOBILE, AL
NAME: STEEN, BILL
CITY-STATE: MOBILE, AL
NAME: FELDMAN, EVAN
CITY-STATE: MOBILE, AL
NAME: SWIM, STEVE
CITY-STATE: UNKNOWN, AL
$
Math Operations
In addition to the textual possibilities AWK
provides, it also offers a full range of arithmetic operators,
including the following:
+ adds numbers together
- subtracts
* multiplies
/ divides
^ performs exponential mathematics
% gives the modulo
++ adds one to the value of a variable
+= assigns the result of an addition operation to a variable
— subtracts one from a variable
-= assigns the result of a subtraction operation to a variable
*= assigns the result of multiplication
/= assigns the result of division
%= assigns the result of a modulo operation
For example, assume the following file exists on your machine detailing the inventory in a hardware store:
$ cat inventory
hammers 5 7.99
drills 2 29.99
punches 7 3.59
drifts 2 4.09
bits 55 1.19
saws 123 14.99
nails 800 .19
screws 80 .29
brads 100 .24
$
The first order of business is to compute the
value of each item's inventory by multiplying the value of the second
field (quantity) by the value of the third field (price):
$ awk '{print $1,"QTY: "$2,"PRICE: "$3,"TOTAL: "$2*$3}' inventory
hammers QTY: 5 PRICE: 7.99 TOTAL: 39.95
drills QTY: 2 PRICE: 29.99 TOTAL: 59.98
punches QTY: 7 PRICE: 3.59 TOTAL: 25.13
drifts QTY: 2 PRICE: 4.09 TOTAL: 8.18
bits QTY: 55 PRICE: 1.19 TOTAL: 65.45
saws QTY: 123 PRICE: 14.99 TOTAL: 1843.77
nails QTY: 800 PRICE: .19 TOTAL: 152
screws QTY: 80 PRICE: .29 TOTAL: 23.2
brads QTY: 100 PRICE: .24 TOTAL: 24
$
If the lines themselves are unimportant, and you
want only to determine exactly how many items are in the store, you can
assign a generic variable to increment by the number of items in each
record:
$ awk '{x=x+$2} {print x}' inventory
5
7
14
16
71
194
994
1074
1174
$
According to this data, 1,174 items are in the
store. The first time through, the variable x had no value, so it took
the value of the first line's second field. The next time through, it
retained the value of the first line and added the value from the
second line, and so on, until it arrived at a cumulative total.
The same process can be applied to determining the total value of the inventory on hand:
$ awk '{x=x+($2*$3)} {print x}' inventory
39.95
99.93
125.06
133.24
198.69
2042.46
2194.46
2217.66
2241.66
$
Thus, the value of the 1,174 items is $2,241.66.
Although this procedure is good for getting a total, it does not look
at all pretty, and it would need sanitizing for an actual report.
Sprucing up the display a bit can be easily accomplished with a few
additions:
$ awk '{x=x+($2*$3)}{print $1,"QTY: "$2,"PRICE: "$3,"TOTAL: "$2*$3,"BAL: "x}' inventory
hammers QTY: 5 PRICE: 7.99 TOTAL: 39.95 BAL: 39.95
drills QTY: 2 PRICE: 29.99 TOTAL: 59.98 BAL: 99.93
punches QTY: 7 PRICE: 3.59 TOTAL: 25.13 BAL: 125.06
drifts QTY: 2 PRICE: 4.09 TOTAL: 8.18 BAL: 133.24
bits QTY: 55 PRICE: 1.19 TOTAL: 65.45 BAL: 198.69
saws QTY: 123 PRICE: 14.99 TOTAL: 1843.77 BAL: 2042.46
nails QTY: 800 PRICE: .19 TOTAL: 152 BAL: 2194.46
screws QTY: 80 PRICE: .29 TOTAL: 23.2 BAL: 2217.66
brads QTY: 100 PRICE: .24 TOTAL: 24 BAL: 2241.66
$
This procedure gives a listing of each record
while assigning a total value to the inventory and keeping a running
balance of the store's inventory.
BEGIN and END
Actions can be specified to take place prior to the actual start of processing or after it has been completed with BEGIN and END statements respectively. BEGIN statements are most commonly used to establish variables or display a header. END statements, on the other hand, can be used to continue processing after the program has finished.
In an earlier example, a complete value of the inventory was generated with the routine
awk '{x=x+($2*$3)} {print x}' inventory
This routine provided a display for each line in
the file as the running total accumulated. There was no other way to
specify it, and not having it print at each line would have resulted in
it never printing. With an END statement, however, this problem can be circumvented:
$ awk '{x=x+($2*$3)} END {print "Total Value of Inventory: "x}' inventory
Total Value of Inventory: 2241.66
$
The variable x
is defined, and it processes for each line; however, no display is
generated until all processing has completed. While it's useful as a
standalone routine, it an also be put with the earlier listing to add
even more information and a more complete report:
$ awk '{x=x+($2*$3)} {print $1,"QTY: "$2,"PRICE:
"$3,"TOTAL: "$2*$3} END {print "Total Value of Inventory: " x}' inventory
hammers QTY: 5 PRICE: 7.99 TOTAL: 39.95
drills QTY: 2 PRICE: 29.99 TOTAL: 59.98
punches QTY: 7 PRICE: 3.59 TOTAL: 25.13
drifts QTY: 2 PRICE: 4.09 TOTAL: 8.18
bits QTY: 55 PRICE: 1.19 TOTAL: 65.45
saws QTY: 123 PRICE: 14.99 TOTAL: 1843.77
nails QTY: 800 PRICE: .19 TOTAL: 152
screws QTY: 80 PRICE: .29 TOTAL: 23.2
brads QTY: 100 PRICE: .24 TOTAL: 24
Total Value of Inventory: 2241.66
$
The BEGIN command words in the same fashion as END,
but it establishes items that need to be done before anything else is
accomplished. The most common purpose of this procedure is to create
headers for reports. The syntax for this routine would resemble
$ awk 'BEGIN {print "ITEM QUANTITY PRICE TOTAL"}'
Input, Output, and Source Files
The AWK tool can read its input from a file, as
was done in all examples up to this point, or it can take input from
the output of another command. For example:
$ sort emp_names | awk '{print $3,$2}'
The input of the awk command is the output from the sort operation. In addition to sort, any other Linux command can be used — for example, grep. This procedure allows you to perform other operations on the file before pulling out selected fields.
Like the shell, AWK uses the output-redirection operators > and >> to put its output into a file rather than to standard output. The symbols react like their counterparts in the shell, so > creates the file if it doesn't exist, and >> appends to the existing file. Examine the following example:
$ awk '{print NR, $1 ) > "/tmp/filez" }' emp_names
$ cat /tmp/filez
1 46012
2 46013
3 46015
4 46017
5 46018
6 46019
7 46021
8 46022
9 46024
10 46026
11 46027
12 46029
$
Examining the syntax of the statement, you can
see that the output redirection is done after the print statement is
complete. You must enclose the file name in quotes, or else it is
simply an uninitialized AWK variable, and the combination of
instructions generates an error from AWK. (If you use the redirection
symbols improperly, AWK gets confused about whether the symbol means
"redirection" or is a relation operator.)
Output into pipes in AWK also resembles the way
the same action would be accomplished in a shell. To send the output of
a print command into a pipe, follow the print command with a pipe
symbol and the name of the command, as in the following:
$ awk '{ print $2 | "sort" }' emp_names
BOGUE
BUCK
DULANEY
DURHAM
FELDMAN
FERGUS
JUNE
KANE
STEEN
SWIM
TUTTLE
WOOD
$
As was the case with output redirection, you
must enclose the command in quotes, and the name of the pipe is the
name of the command being executed.
Commands used by AWK can come from two
locations. First, they can be specified on the command line, as
illustrated. Second, they can come from a source file. If such is the
case, AWK is alerted to this occurrence by means of the -f option. To illustrate:
$ cat awklist
{print $3,$2}
{print $4,$5,"\n"}
$
$ awk -f awklist emp_names
EVAN DULANEY
MOBILE AL
JEFF DURHAM
MOBILE AL
BILL STEEN
MOBILE AL
EVAN FELDMAN
MOBILE AL
STEVE SWIM
UNKNOWN AL
ROBERT BOGUE
PHOENIX AR
MICAH JUNE
PHOENIX AR
SHERYL KANE
UNKNOWN AR
WILLIAM WOOD
MUNCIE IN
SARAH FERGUS
MUNCIE IN
SARAH BUCK
MUNCIE IN
BOB TUTTLE
MUNCIE IN
$
Notice that the apostrophes are not used
anywhere within the source file or when calling it at the command line.
They are only for use in differentiating the commands on the command
line from file names.
If simple output cannot handle the intricate detail you want in your programs, try the more complex output available with the printf command, the syntax for which is
printf( format, value, value ...)
This syntax is like that of the printf
command in the C language, and the specifications for the format are
the same. You define the format by inserting a specification that
defines how the value is to be printed. The format specification
consists of a % followed by a letter. Like the print command, printf does not have to be enclosed in parentheses, but using them is considered good practice.
The following table lists the various specifications available for the printf command.
Specification | Description |
%c | Prints a single ASCII character |
%d | Prints a decimal number |
%e | Prints a scientific notation representation of numbers |
%f | Prints a floating-point representation |
%g | Prints %e or %f; whichever is shorter |
%o | Prints an unsigned octal number |
%s | Prints an ASCII string |
%x | Prints an unsigned hexadecimal number |
%% | Prints a percent sign; no conversion is performed |
|