====== 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.|
|LINT|Provides dynamic control of the –lint option.|
|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.|
|PROCINFO|Information about the process.|
|RLENGTH|The length of the string matched by the match function.|
|RSTART|The first position in the string matched by match function.|
|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".|
|TEXTDOMAIN|The text domain of the AWK program.  For compatibility with GNU **gettext**.  The default value is "messages".|


----


===== ARGC =====

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

<code awk>
awk 'BEGIN {print "Arguments =", ARGC}' One Two Three Four
</code>

returns:

<code bash>
Arguments = 5
</code>

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

----

===== ARGIND =====

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

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

returns:

<code bash>
ARGIND   =  1
Filename =  junk1
ARGIND   =  2
Filename =  junk2
ARGIND   =  3
Filename =  junk3
</code>

----

===== ARGV =====

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

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

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

returns:

<code bash>
ARGV[0] = awk
ARGV[1] = one
ARGV[2] = two
ARGV[3] = three
</code>
----

===== 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.

<code awk>
awk 'BEGIN { print "Conversion Format =", CONVFMT }'
</code>

returns:

<code bash>
Conversion Format = %.6g
</code>

----

===== ENVIRON =====

It is an associative array of environment variables.

<code awk>
awk 'BEGIN { print ENVIRON["USER"] }'
</code>

returns:

<code bash>
peter
</code>

<WRAP info>
**NOTE:**  To find names of other environment variables, use the **env** command.
</WRAP>

----

===== ERRNO =====

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

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

returns:

<code bash>
Error: No such file or directory
</code>

----

===== 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.

<code awk>
awk 'END {print FILENAME}' test.txt
</code>

returns:

<code bash>
test.txt
</code>

<WRAP info>
**NOTE:** Please note that FILENAME is undefined in the BEGIN block.
</WRAP>

----

===== 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.

<code bash>
echo -e "One Two\nOne Two Three\nOne Two Three Four" | awk 'FNR < 3'
</code>

returns:

<code>
One Two
One Two Three
</code>

<WRAP info>
**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 awk>
awk 'BEGIN{IGNORECASE = 1} /peter/' test.txt
</code>

returns:

<code bash>
10   Peter     Terence    Roux        45
</code>

<WRAP info>
**NOTE:**  If IGNORECASE does not work then try:

<code bash>
awk 'tolower($0) ~ /peter/' test.txt
</code>

</WRAP>

----

===== 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 awk>
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>

<WRAP info>
**NOTE:**  This only works with GAWK, not AWK.
</WRAP>

----

===== 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 awk>
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 awk>
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 awk>
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 awk>
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 awk>
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 awk>
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 awk>
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 awk>
awk 'BEGIN { print "SUBSEP = " SUBSEP }' | cat -vte
</code>

returns:

<code bash>
SUBSEP = ^\$
</code>

----

===== $0 =====

It represents the entire input record.

<code awk>
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 awk>
awk 'BEGIN { print TEXTDOMAIN }'
</code>

returns:

<code bash>
messages
</code>

<WRAP info>
**NOTE:**  The above output shows English text due to en_GB locale.
</WRAP>


----

===== $n =====

It represents the nth field in the current record where the fields are separated by FS.

<code awk>
awk '{print $2 "\t" $5}' test.txt
</code>

returns:

<code bash>
Peter   45
Virginia     45
Felix   5
David   48
Bob   16
Adam   23
</code>

----