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<A NAME="PAGENUM-167"><P>Page 167</P></A>
<TABLE>
<TR><TD>
*/%
</TD><TD>
Multiplication, division, and modulus.
</TD></TR><TR><TD>
+_!
</TD><TD>
Unary plus, unary minus, and logical negation.
</TD></TR><TR><TD>
^
</TD><TD>
Exponentiation (** may also be used, and **=
for the assignment operator).
</TD></TR><TR><TD>
++ __
</TD><TD>
Increment and decrement, both prefix and postfix.
</TD></TR><TR><TD>
$
</TD><TD>
Field reference.
</TD></TR></TABLE>
<P><B>
CONTROL STATEMENTS
</B></P>
<P>The control statements are as follows:
</P>
<!-- CODE //-->
<PRE>
if (condition) statement [ else statement ]
while (condition) statement
do statement while (condition)
for (expr1; expr2; expr3) statement
for (var in array) statementbreak
continue
delete array[index]
delete array
exit [ expression ]
{ statements }
</PRE>
<!-- END CODE //-->
<P><B>
I/O STATEMENTS
</B></P>
<P>The input/output statements are as follows:
</P>
<TABLE>
<TR><TD>
close(filename)
</TD><TD>
Close file (or pipe, see paragraph following this list).
</TD></TR><TR><TD>
getline
</TD><TD>
Set $0 from next input record; set
NF, NR, FNR.
</TD></TR><TR><TD>
getline <file
</TD><TD>
Set $0 from next record of
file; set NF.
</TD></TR><TR><TD>
getline var
</TD><TD>
Set var from next input record; set
NF, FNR.
</TD></TR><TR><TD>
getline var <file
</TD><TD>
Set var from next record of
file.
</TD></TR><TR><TD>
next
</TD><TD>
Stop processing the current input record. The next input record is read and processing
starts over with the first pattern in the awk program. If the end of the input data is reached,
the END block(s), if any, are executed.
</TD></TR><TR><TD>
next file
</TD><TD>
Stop processing the current input file. The next input record read comes from the
next input file. FILENAME is updated, FNR is reset to
1, and processing starts over with the first pattern in the
awk program. If the end of the input data is reached, the
END block(s), if any, are executed.
</TD></TR><TR><TD>
print
</TD><TD>
Prints the current record.
</TD></TR><TR><TD>
print expr-list
</TD><TD>
Prints expressions. Each expression is separated by the value of the
OFS variable. The output record is terminated with the value of the
ORS variable.
</TD></TR><TR><TD>
print expr-list >file
</TD><TD>
Prints expressions on
file. Each expression is separated by the value of the
OFS variable. The output record is terminated with the value of the
ORS variable.
</TD></TR><TR><TD>
printf fmt, expr-list
</TD><TD>
Format and print.
</TD></TR><TR><TD>
printf fmt, expr-list >file
</TD><TD>
Format and print on
file.
</TD></TR><TR><TD>
system(cmd-line)
</TD><TD>
Execute the command
cmd-line, and return the exit status. (This may not be available on
-POSIX systems.)
</TD></TR></TABLE>
<P>Other input/output redirections are also allowed. For
print and printf, >>file appends output to the
file, while | command writes on a pipe. In a similar fashion,
command | getline pipes into getline. The getline command will return
0 on end of file, and _1 on an error.
</P>
<P><B>
THE PRINTF STATEMENT
</B></P>
<P>The awk versions of the printf statement and
sprintf() function accept the following conversion specification formats:
</P>
<TABLE>
%c
<TR><TD>
An ASCII character. If the argument used for
%c is numeric, it is treated as a character and
printed. Otherwise, the argument is assumed to be a string, and the only first character of that string is printed.
</TD></TR></TABLE>
<A NAME="PAGENUM-168"><P>Page 168</P></A>
<TABLE>
<TR><TD>
%d
</TD><TD>
A decimal number (the integer part).
</TD></TR><TR><TD>
%i
</TD><TD>
Just like %d.
</TD></TR><TR><TD>
%e
</TD><TD>
A floating-point number of the form
[_]d.ddddddE[+_]dd.
</TD></TR><TR><TD>
%f
</TD><TD>
A floating-point number of the form
[_]ddd.dddddd.
</TD></TR><TR><TD>
%g
</TD><TD>
Use e or f conversion, whichever is shorter, with nonsignificant zeros suppressed.
</TD></TR><TR><TD>
%o
</TD><TD>
An unsigned octal number (again, an integer).
</TD></TR><TR><TD>
%s
</TD><TD>
A character string.
</TD></TR><TR><TD>
%x
</TD><TD>
An unsigned hexadecimal number (an integer).
</TD></TR><TR><TD>
%X
</TD><TD>
Like %x, but using ABCDEF instead of abcdef.
</TD></TR><TR><TD>
%%
</TD><TD>
A single % character; no argument is converted.
</TD></TR></TABLE>
<P>There are optional, additional parameters that may lie between the
% and the control letter:
</P>
<TABLE>
<TR><TD>
_
</TD><TD>
The expression should be left-justified within its field.
</TD></TR><TR><TD>
width
</TD><TD>
The field should be padded to this width. If the number has a leading zero, then the field will be
padded with zeros. Otherwise, it is padded with blanks. This applies even to the nonnumeric output formats.
</TD></TR><TR><TD>
.prec
</TD><TD>
A number indicating the maximum width of strings or digits to the right of the decimal point.
</TD></TR></TABLE>
<P>The dynamic width and prec capabilities of the C
printf() routines are supported. A * in place of either the
width or prec specifications will cause their values to be taken from the argument list to
printf or sprintf().
</P>
<P><B>
SPECIAL FILEMANES
</B></P>
<P>When doing I/O redirection from either print or
printf into a file, or via getline from a file,
gawk recognizes certain special filenames internally. These filenames allow access to open file descriptors inherited from
gawk's parent process (usually the shell). Other special filenames provide access information about the running
gawk process. The filenames are
</P>
<TABLE>
<TR><TD>
/dev/pid
</TD><TD>
Reading this file returns the process ID of the current process, in decimal, terminated with a newline.
</TD></TR><TR><TD>
/dev/ppid
</TD><TD>
Reading this file returns the parent process ID of the current process, in decimal, terminated with
a newline.
</TD></TR><TR><TD>
/dev/pgrpid
</TD><TD>
Reading this file returns the process group ID of the current process, in decimal, terminated with
a newline.
</TD></TR><TR><TD>
/dev/user
</TD><TD>
Reading this file returns a single record terminated with a newline. The fields are separated with blanks.
$1 is the value of the getuid(2) system call, $2 is the value of the
geteuid(2) system call, $3 is the value of the
getgid(2) system call, and $4 is the value of the
getegid( 2) system call. If there are any additional
fields, they are the group IDs returned by
getgroups(2). Multiple groups may not be supported on all systems.
</TD></TR><TR><TD>
/dev/stdin
</TD><TD>
The standard input.
</TD></TR><TR><TD>
/dev/stdout
</TD><TD>
The standard output.
</TD></TR><TR><TD>
/dev/stderr
</TD><TD>
The standard error output.
</TD></TR><TR><TD>
/dev/fd/n
</TD><TD>
The file associated with the open file descriptor
n.
</TD></TR></TABLE>
<P>These are particularly useful for error messages. For example, you could use
</P>
<!-- CODE SNIP //-->
<PRE>
print "You blew it!" > "/dev/stderr"
</PRE>
<!-- END CODE SNIP //-->
<P>whereas you would otherwise have to use
</P>
<!-- CODE SNIP //-->
<PRE>
print "You blew it!" j "cat 1>&2"
</PRE>
<!-- END CODE SNIP //-->
<P>These filenames may also be used on the command line to name data files.
</P>
<P><B>
NUMERIC FUNCTIONS
</B></P>
<P>awk has the following predefined arithmetic functions:
</P>
<TABLE>
<TR><TD>
atan2(y, x)
</TD><TD>
Returns the arctangent of y/x in radians.
</TD></TR><TR><TD>
cos(expr)
</TD><TD>
Returns the cosine in radians.
</TD></TR></TABLE>
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