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13.8. Alphabetical Summary of Commands

The following alphabetical list of statements and functions includes all that are available in gawk in Linux.

atan2

atan2(y,x)

Return the arctangent of y/x in radians.

break

break

Exit from a while or for loop.

close

close(filename-expr)

close(command-expr)

Close a file read by a getline command or a pipe; takes as an argument the same expression that opened the pipe or file.

continue

continue

Begin next iteration of while or for loop without reaching the bottom.

cos

cos(x)

Return the cosine of x, an angle in radians.

delete

delete array[element]

delete array

Delete element of array. If no element is specified, all elements are deleted.

do

do

body

while(expr)

Looping statement. Execute statements in body, then evaluate expr. If expr is true, execute body again.

exit

exit

Do not execute remaining instruction, and read no new input. END procedures will be executed.

exp

exp(arg)

Return the natural exponent of arg (the inverse of log).

fflush

fflush(filename)

Flushes output to filename; default is the standard output.

for

for(i=lower ; i<=upper ; i++)

command

While the value of variable i is in the range between lower and upper, do command. A series of commands must be put within braces. <= or any relational operator can be used; ++ or -- can be used to increment or decrement the variable.

for

for(item in array)

command

For each item in an associative array, do command. Multiple commands must be put inside braces. Refer to each element of the array as array[item]. Elements of gawk arrays are stored in an order that enables access of any element in essentially equivalent time. This order may appear to be indiscriminate; if the output is desired in sorted order, you must pipe it through the sort command.

function

function name(parameter-list) {

statements

}

Create name as a user-defined function consisting of gawk statements that apply to the specified list of parameters.

gensub

gensub(r,s,n,t)

Substitute s for the nth match of regular expression r in the string t. Leave t unchanged, but return new string as the result. If n is "g" or "G" change all matches. If t is not supplied, it defaults to $0.

getline

getline [varhairsp;] [<file]

command | getline [var]

The first form reads input from file or the next file on the command line, and the second form reads the output of command. Both forms read one line at a time, and each time the statement is executed it gets the next line of input. The line of input is assigned to $0 and is parsed into fields, setting NF, NR, and FNR. If var is specified, the result is assigned to var, and neither $0 nor NF is changed. Thus, if the result is assigned to a variable, the current line does not change. getline is actually a function, and it returns 1 if it reads a record successfully, 0 at EOF, and -1 if for some reason it is otherwise unsuccessful.

gsub

gsub(r,s,t)

Globally substitute s for each match of the regular expression r in the string t. Return the number of substitutions. If t is not supplied, it defaults to $0.

if

if (condition)

command1

[else

command2]

If condition is true, do command1; otherwise, do command2. Condition can be an expression using any of the relational operators <, <=, ==, !=, >=, or >, as well as the pattern-matching operator ~. A series of commands must be put within braces.

Example

The following lines determine whether the first word in each line starts with A, uppercase or lowercase:

if ($1 ~ /[Aa]*/)
    ...Begins with A or a
index

index(substr,str)

Return the position of a substring in a string. Returns 0 if substr is not contained in str.

int

int(arg)

Return the integer part of arg.

length

length(arg)

Return the length of arg. If arg is not supplied, $0 is assumed.

log

log(arg)

Return the natural logarithm of arg (the inverse of exp).

match

match(s,r)

Return position in s where regular expression r first matches or 0 if no occurrences are found. Sets the value of RSTART and RLENGTH.

next

next

Read next input line and start new cycle through pattern/procedures statements.

nextfile

nextfile

Skip to the next file on the gawk command line and start new cycle through pattern/procedures statements.

print

print [args] [destination]

Print args on output. Literal strings must be quoted. Fields are printed in the order they are listed. If separated by commas in the argument list, they are separated in the output by the character specified by OFS. If separated by spaces, they are concatenated in the output. destination is a shell redirection or pipe expression (e.g., > file) that redirects the default output.

printf

printf [format [, expressions]]

Formatted print statement. Expressions or variables can be formatted according to instructions in the format argument. The number of expressions must correspond to the number specified in the format sections.

format follows the conventions of the C-language printf statement. Here are a few of the most common formats:

%s

A string.

%d

A decimal number.

%n.mf

A floating point number. n = total number of digits; m = number of digits after decimal point.

%[-]nc

n specifies minimum field length for format type c, while - left-justifies value in field; otherwise, value is right-justified.

Field widths are adjustable. For example, %3.2f limits a floating-point number to a total width of three digits, with two digits after the decimal point.

format also can contain embedded escape sequences, \n (newline) and \t (tab) being the most common. Spaces and literal text can be placed in the format argument by quoting the entire argument. If there are multiple expressions to be printed, multiple formats should be specified.

Example

Using the script:

{printf ("The sum on line %s is %d.\n", NR, $1+$2)}

the following input line:

5   5

produces this output, followed by a newline:

The sum on line 1 is 10.
rand

rand( )

Generate a random number between 0 and 1. This function returns the same series of numbers each time the script is executed, unless the random number generator is seeded using the srand function.

return

return [expr]

Used at end of user-defined functions to exit function, returning the value of expr.

sin

sin(x)

Return the sine of x, an angle in radians.

split

split(string,array[,sep])

Split string into elements of array array[1],...,array[n]. The string is split at each occurrence of separator sep. If sep is not specified, FS is used. If sep is a null string, a split is performed on every character. The number of array elements created is returned.

sprintf

sprintf [format [, expression(s)]]

Return the value of one or more expressions, using the specified format (see printf). Data is formatted but not printed.

sqrt

sqrt(arg)

Return square root of arg.

srand

srand(expr)

Use expr to set a new seed for random number generator. Default is time of day.

strftime

strftime([format [,timestamp]])

Format timestamp according to format. Return the formatted string. The timestamp is a time-of-day value in seconds since midnight, January 1, 1970, UTC. The format string is similar to that of sprintf. (See the example for systime.) If timestamp is omitted, it defaults to the current time. If format is omitted, it defaults to a value that produces output similar to that of date.

sub

sub(r,s,t)

Substitute s for first match of the regular expression r in the string t. Return 1 if successful; 0 otherwise. If t is not supplied, the default is $0.

substr

substr(string,m[,n])

Return substring of string beginning at character position m and consisting of the next n characters. If n is omitted, include all characters to the end of string.

system

system(command)

Execute the specified shell command and return its status. The status of the command that is executed typically indicates its success (1), completion (0), or unexpected error (-1). The output of the command is not available for processing within the gawk script.

systime

systime()

Return number of seconds since midnight UTC, January 1, 1970.

Example

Log the start and end times of a data-processing program:

BEGIN {
	now = systime()
	mesg = strftime("Started at %m/%d/%Y %H:%M:%S", now)
	print mesg
}
process data ...
END {
	now = systime()
	mesg = strftime("Ended at %m/%d/%Y %H:%M:%S", now)
	print mesg
}
tolower

tolower(str)

Translate all uppercase characters in str to lowercase and return the new string.

toupper

toupper(str)

Translate all lowercase characters in str to uppercase and return the new string.

while

while (condition)

command

Do command while condition is true (see if for a description of allowable conditions). A series of commands must be put within braces.



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