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AWK - AWK Variables

AWK provides several built-in variables.

They play an important role while writing AWK scripts.

Here is a list of some of the built-in variables supported by AWK:

Variable	Details
ARGC	The number of command line arguments.
ARGIND	The index in ARGV of the current file being processed.
ARGV	Array of command line arguments. The array is indexed from 0 to ARGC - 1.
BINMODE	Specifies use of “binary” mode for all file I/O.
CONVFMT	The conversion format for numbers, “%.6g”, by default.
ENVIRON	Environment Variables.
FIELDWIDTHS	A white-space separated list of field widths. When set the input is parsed into fields of fixed width, instead of using the value of the FS variable as the field separator.
FILENAME	Current filename.
FNR	The input record number in the current input file.
FPAT	A regular expression describing the contents of the fields in a record. When set the input is parsed into fields, where the fields match the regular expression, instead of using the value of the FS variable as the field separator.
FS	The input field separator, a space by default.
IGNORECASE	Controls the case-sensitivity of all regular expression and string operations.
NF	The number of fields in the current input record.
NR	The total number of input records seen so far.
OFMT	The output format for numbers, “%.6g”, by default.
OFS	The output field separator, a space by default.
ORS	The output record separator, by default a newline.
RS	The input record separator, by default a newline.
RT	The record terminator.
SUBSEP	The character used to separate multiple subscripts in array elements, by default “\034”.

ARGC

It implies the number of arguments provided at the command line.

awk 'BEGIN {print "Arguments =", ARGC}' One Two Three Four

returns:

Arguments = 5

NOTE: The number of arguments reported is one more than the variables passed; as this also includes the calling program as the first argument.

ARGIND

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

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

returns:

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

ARGV

It is an array that stores the command-line arguments.

The array's valid index ranges from 0 to ARGC-1.

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

returns:

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

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.

CONVFMT

It represents the conversion format for numbers.

Its default value is %.6g.

awk 'BEGIN { print "Conversion Format =", CONVFMT }'

returns:

Conversion Format = %.6g

ENVIRON

It is an associative array of environment variables.

awk 'BEGIN { print ENVIRON["USER"] }'

returns:

peter

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

ERRNO

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

awk 'BEGIN { ret = getline < "junk.txt"; if (ret == -1) print "Error:", ERRNO }'

returns:

Error: No such file or directory

FIELDWIDTHS

A space separated list 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.

FILENAME

It represents the current file name.

awk 'END {print FILENAME}' test.txt

returns:

test.txt

NOTE: Please note that FILENAME is undefined in the BEGIN block.

FNR

It is similar to NR, but relative to the current file.

It is useful when AWK is operating on multiple files.

It represents the number of the current record in the current file.

NOTE: The Value of FNR resets with a new file. </WRAP> —- ===== FS ===== It represents the (input) field separator and its default value is space. You can also change this by using -F command line option. <code awk> awk 'BEGIN {print “FS = ” FS}' | cat -vte </code> returns: <code bash> FS = $ </code> —- ===== IGNORECASE ===== When this variable is set, GAWK becomes case-insensitive. <code bash> awk 'BEGIN{IGNORECASE = 1} /peter/' test.txt </code> returns: <code bash> 10 Peter Terence Roux 45 </code> —- ===== LINT ===== It provides dynamic control of the –lint option from the GAWK program. When this variable is set, GAWK prints lint warnings. When assigned the string value fatal, lint warnings become fatal errors, exactly like –lint=fatal. <code bash> awk 'BEGIN {LINT = 1; a}' </code> returns: <code bash> awk: cmd. line:1: warning: reference to uninitialized variable `a' awk: cmd. line:1: warning: statement has no effect </code> —- ===== NF ===== It represents the number of fields in the current record. For instance, the following example prints only those lines that contain more than two fields. <code bash> echo -e “One Two\nOne Two Three\nOne Two Three Four” | awk 'NF > 2' </code> returns: <code bash> One Two Three One Two Three Four </code> —- ===== 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. <code bash> echo -e “One Two\nOne Two Three\nOne Two Three Four” | awk 'NR < 3' </code> returns: <code bash> One Two One Two Three </code> —- ===== OFMT ===== It represents the output format number and its default value is %.6g. <code bash> awk 'BEGIN {print “OFMT = ” OFMT}' </code> returns: <code bash> OFMT = %.6g </code> —- ===== OFS ===== It represents the output field separator and its default value is space. <code bash> awk 'BEGIN {print “OFS = ” OFS}' | cat -vte </code> returns: <code bash> OFS = $ </code> —- ===== ORS ===== It represents the output record separator and its default value is newline. <code bash> awk 'BEGIN {print “ORS = ” ORS}' | cat -vte </code> returns: <code bash> ORS = $ $ </code> —- ===== PROCINFO ===== This is an associative array containing information about the process, such as real and effective UID numbers, process ID number, and so on. <code bash> awk 'BEGIN { print PROCINFO[“pid”] }' </code> returns: <code bash> 30510 </code> —- ===== 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. <code bash> awk 'BEGIN { if (match(“One Two Three”, “re”)) { print RLENGTH } }' </code> returns: <code bash> 2 </code> —- ===== RS ===== It represents (input) record separator and its default value is newline. <code bash> awk 'BEGIN {print “RS = ” RS}' | cat -vte </code> returns: <code bash> RS = $ $ </code> —- ===== RSTART ===== It represents the first position in the string matched by match function. <code bash> awk 'BEGIN { if (match(“One Two Three”, “Thre”)) { print RSTART } }' </code> returns: <code bash> 9 </code> —- ===== SUBSEP ===== It represents the separator character for array subscripts and its default value is \034. <code bash> awk 'BEGIN { print “SUBSEP = ” SUBSEP }' | cat -vte </code> returns: <code bash> SUBSEP = ^\$ </code> —- ===== $0 ===== It represents the entire input record. <code bash> awk '{print $0}' test.txt </code> returns: <file> 10 Peter Terence Roux 45 11 Virginia Genevieve Roux 45 12 Felix Devon Roux 5 13 David Bruce Stevenson 48 14 Bob James Smith 16 48 Adam Winter Ridley 23 </file> —- ===== TEXTDOMAIN ===== It represents the text domain of the AWK program. It is used to find the localized translations for the program's strings. <code bash> awk 'BEGIN { print TEXTDOMAIN }' </code> returns: <code bash> messages </code>

NOTE: The above output shows English text due to en_GB locale.

—- ===== $n ===== It represents the nth field in the current record where the fields are separated by FS. <code bash> awk '{print $2 “\t” $5}' test.txt </code> returns: <code bash> Peter 45 Virginia 45 Felix 5 David 48 Bob 16 Adam 23 </code> —-

awk/awk_variables.1588790884.txt.gz · Last modified: 2020/07/15 09:30 (external edit)

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Table of Contents

AWK - AWK Variables

ARGC

ARGIND

ARGV

BINMODE

CONVFMT

ENVIRON

ERRNO

FIELDWIDTHS

FILENAME

FNR