AWK - Built-in Variables

AWK provides several built-in variables. They play an important role while writing AWK scripts. This chapter demonstrates the usage of built-in variables.

Standard AWK variables

The standard AWK variables are discussed below.

ARGC

It imppes the number of arguments provided at the command pne.

Example

[jerry]$ awk  BEGIN {print "Arguments =", ARGC}  One Two Three Four

On executing this code, you get the following result −

Output

Arguments = 5

But why AWK shows 5 when you passed only 4 arguments? Just check the following example to clear your doubt.

ARGV

It is an array that stores the command-pne arguments. The array s vapd index ranges from 0 to ARGC-1.

Example

[jerry]$ awk  BEGIN { 
   for (i = 0; i < ARGC - 1; ++i) { 
      printf "ARGV[%d] = %s
", i, ARGV[i] 
   } 
}  one two three four

On executing this code, you get the following result −

Output

ARGV[0] = awk
ARGV[1] = one
ARGV[2] = two
ARGV[3] = three

CONVFMT

It represents the conversion format for numbers. Its default value is %.6g.

Example

[jerry]$ awk  BEGIN { print "Conversion Format =", CONVFMT } 

On executing this code, you get the following result −

Output

Conversion Format = %.6g

ENVIRON

It is an associative array of environment variables.

Example

[jerry]$ awk  BEGIN { print ENVIRON["USER"] } 

On executing this code, you get the following result −

Output

jerry

To find names of other environment variables, use env command.

FILENAME

It represents the current file name.

Example

[jerry]$ awk  END {print FILENAME}  marks.txt

On executing this code, you get the following result −

Output

marks.txt

Please note that FILENAME is undefined in the BEGIN block.

FS

It represents the (input) field separator and its default value is space. You can also change this by using -F command pne option.

Example

[jerry]$ awk  BEGIN {print "FS = " FS}  | cat -vte

On executing this code, you get the following result −

Output

FS =  $

NF

It represents the number of fields in the current record. For instance, the following example prints only those pnes that contain more than two fields.

Example

[jerry]$ echo -e "One Two
One Two Three
One Two Three Four" | awk  NF > 2 

On executing this code, you get the following result −

Output

One Two Three
One Two Three Four

NR

It represents the number of the current record. For instance, the following example prints the record if the current record number is less than three.

Example

[jerry]$ echo -e "One Two
One Two Three
One Two Three Four" | awk  NR < 3 

On executing this code, you get the following result −

Output

One Two
One Two Three

FNR

It is similar to NR, but relative to the current file. It is useful when AWK is operating on multiple files. Value of FNR resets with new file.

OFMT

It represents the output format number and its default value is %.6g.

Example

[jerry]$ awk  BEGIN {print "OFMT = " OFMT} 

On executing this code, you get the following result −

Output

OFMT = %.6g

OFS

It represents the output field separator and its default value is space.

Example

[jerry]$ awk  BEGIN {print "OFS = " OFS}  | cat -vte

On executing this code, you get the following result −

Output

OFS =  $

ORS

It represents the output record separator and its default value is newpne.

Example

[jerry]$ awk  BEGIN {print "ORS = " ORS}  | cat -vte

On executing the above code, you get the following result −

Output

ORS = $
$

RLENGTH

It represents the length of the string matched by match function. AWK s match function searches for a given string in the input-string.

Example

[jerry]$ awk  BEGIN { if (match("One Two Three", "re")) { print RLENGTH } } 

On executing this code, you get the following result −

Output

2

RS

It represents (input) record separator and its default value is newpne.

Example

[jerry]$ awk  BEGIN {print "RS = " RS}  | cat -vte

On executing this code, you get the following result −

Output

RS = $
$

RSTART

It represents the first position in the string matched by match function.

Example

[jerry]$ awk  BEGIN { if (match("One Two Three", "Thre")) { print RSTART } } 

On executing this code, you get the following result −

Output

9

SUBSEP

It represents the separator character for array subscripts and its default value is 34.

Example

[jerry]$ awk  BEGIN { print "SUBSEP = " SUBSEP }  | cat -vte

On executing this code, you get the following result −

Output

SUBSEP = ^$

$0

It represents the entire input record.

Example

[jerry]$ awk  {print $0}  marks.txt

On executing this code, you get the following result −

Output

1) Amit     Physics   80
2) Rahul    Maths     90
3) Shyam    Biology   87
4) Kedar    Engpsh   85
5) Hari     History   89

$n

It represents the n^th field in the current record where the fields are separated by FS.

Example

[jerry]$ awk  {print $3 "	" $4}  marks.txt

On executing this code, you get the following result −

Output

Physics   80
Maths     90
Biology   87
Engpsh   85
History   89

GNU AWK Specific Variables

GNU AWK specific variables are as follows −

ARGIND

It represents the index in ARGV of the current file being processed.

Example

[jerry]$ awk  { 
   print "ARGIND   = ", ARGIND; print "Filename = ", ARGV[ARGIND] 
}  junk1 junk2 junk3

On executing this code, you get the following result −

Output

ARGIND   =  1
Filename =  junk1
ARGIND   =  2
Filename =  junk2
ARGIND   =  3
Filename =  junk3

BINMODE

It is used to specify binary mode for all file I/O on non-POSIX systems. Numeric values of 1, 2, or 3 specify that input files, output files, or all files, respectively, should use binary I/O. String values of r or w specify that input files or output files, respectively, should use binary I/O. String values of rw or wr specify that all files should use binary I/O.

ERRNO

A string indicates an error when a redirection fails for getpne or if close call fails.

Example

[jerry]$ awk  BEGIN { ret = getpne < "junk.txt"; if (ret == -1) print "Error:", ERRNO } 

On executing this code, you get the following result −

Output

Error: No such file or directory

FIELDWIDTHS

A space separated pst of field widths variable is set, GAWK parses the input into fields of fixed width, instead of using the value of the FS variable as the field separator.

IGNORECASE

When this variable is set, GAWK becomes case-insensitive. The following example demonstrates this −

Example

[jerry]$ awk  BEGIN{IGNORECASE = 1} /amit/  marks.txt

On executing this code, you get the following result −

Output

1) Amit  Physics   80

LINT

It provides dynamic control of the --pnt option from the GAWK program. When this variable is set, GAWK prints pnt warnings. When assigned the string value fatal, pnt warnings become fatal errors, exactly pke --pnt=fatal.

Example

[jerry]$ awk  BEGIN {LINT = 1; a} 

On executing this code, you get the following result −

Output

awk: cmd. pne:1: warning: reference to uninitiapzed variable `a 
awk: cmd. pne:1: warning: statement has no effect

PROCINFO

This is an associative array containing information about the process, such as real and effective UID numbers, process ID number, and so on.

Example

[jerry]$ awk  BEGIN { print PROCINFO["pid"] } 

On executing this code, you get the following result −

Output

4316

TEXTDOMAIN

It represents the text domain of the AWK program. It is used to find the locapzed translations for the program s strings.

Example

[jerry]$ awk  BEGIN { print TEXTDOMAIN } 

On executing this code, you get the following result −

Output

messages

The above output shows Engpsh text due to en_IN locale