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Most awk variables are available for you to use for your own
purposes; they never change except when your program assigns values to
them, and never affect anything except when your program examines them.
A few variables have special built-in meanings. Some of them awk
examines automatically, so that they enable you to tell awk how
to do certain things. Others are set automatically by awk, so
that they carry information from the internal workings of awk to
your program.
This chapter documents all the built-in variables of gawk. Most
of them are also documented in the chapters where their areas of
activity are described.
awk
This is a list of the variables which you can change to control how
awk does certain things.
CONVFMT
awk to control conversion of numbers to
strings (see section Conversion of Strings and Numbers).
It works by being passed, in effect, as the first argument to the
sprintf function. Its default value is "%.6g".
CONVFMT was introduced by the POSIX standard.
FIELDWIDTHS
gawk
how to manage input with fixed, columnar boundaries. It is an
experimental feature that is still evolving. Assigning to FIELDWIDTHS
overrides the use of FS for field splitting.
See section Reading Fixed-width Data, for more information.
If gawk is in compatibility mode
(see section Invoking awk), then FIELDWIDTHS
has no special meaning, and field splitting operations are done based
exclusively on the value of FS.
FS
FS is the input field separator
(see section Specifying how Fields are Separated).
The value is a single-character string or a multi-character regular
expression that matches the separations between fields in an input
record.
The default value is " ", a string consisting of a single
space. As a special exception, this value actually means that any
sequence of spaces and tabs is a single separator. It also causes
spaces and tabs at the beginning or end of a line to be ignored.
You can set the value of FS on the command line using the
`-F' option:
awk -F, 'program' input-files
If gawk is using FIELDWIDTHS for field-splitting,
assigning a value to FS will cause gawk to return to
the normal, regexp-based, field splitting.
IGNORECASE
IGNORECASE is nonzero, then all regular expression
matching is done in a case-independent fashion. In particular, regexp
matching with `~' and `!~', and the gsub index,
match, split and sub functions all ignore case when
doing their particular regexp operations. Note: since field
splitting with the value of the FS variable is also a regular
expression operation, that too is done with case ignored.
See section Case-sensitivity in Matching.
If gawk is in compatibility mode
(see section Invoking awk), then IGNORECASE has
no special meaning, and regexp operations are always case-sensitive.
OFMT
awk to control conversion of numbers to
strings (see section Conversion of Strings and Numbers) for
printing with the print statement.
It works by being passed, in effect, as the first argument to the
sprintf function. Its default value is "%.6g".
Earlier versions of awk also used OFMT to specify the
format for converting numbers to strings in general expressions; this
has been taken over by CONVFMT.OFS
print statement. Its
default value is " ", a string consisting of a single space.
ORS
print statement. Its default value is a string containing a
single newline character, which could be written as "\n".
(See section Output Separators.)RS
awk's input record separator. Its default value is a string
containing a single newline character, which means that an input record
consists of a single line of text.
(See section How Input is Split into Records.)SUBSEP
SUBSEP is the subscript separator. It has the default value of
"\034", and is used to separate the parts of the name of a
multi-dimensional array. Thus, if you access foo[12,3], it
really accesses foo["12\0343"]
(see section Multi-dimensional Arrays).
This is a list of the variables that are set automatically by awk
on certain occasions so as to provide information to your program.
ARGC
ARGV
awk programs are stored in
an array called ARGV. ARGC is the number of command-line
arguments present. See section Invoking awk.
ARGV is indexed from zero to ARGC - 1. For example:
awk 'BEGIN {
for (i = 0; i < ARGC; i++)
print ARGV[i]
}' inventory-shipped BBS-list
In this example, ARGV[0] contains "awk", ARGV[1]
contains "inventory-shipped", and ARGV[2] contains
"BBS-list". The value of ARGC is 3, one more than the
index of the last element in ARGV since the elements are numbered
from zero.
The names ARGC and ARGV, as well the convention of indexing
the array from 0 to ARGC - 1, are derived from the C language's
method of accessing command line arguments.
Notice that the awk program is not entered in ARGV. The
other special command line options, with their arguments, are also not
entered. But variable assignments on the command line are
treated as arguments, and do show up in the ARGV array.
Your program can alter ARGC and the elements of ARGV.
Each time awk reaches the end of an input file, it uses the next
element of ARGV as the name of the next input file. By storing a
different string there, your program can change which files are read.
You can use "-" to represent the standard input. By storing
additional elements and incrementing ARGC you can cause
additional files to be read.
If you decrease the value of ARGC, that eliminates input files
from the end of the list. By recording the old value of ARGC
elsewhere, your program can treat the eliminated arguments as
something other than file names.
To eliminate a file from the middle of the list, store the null string
("") into ARGV in place of the file's name. As a
special feature, awk ignores file names that have been
replaced with the null string.
ARGIND
ARGV of the current file being processed.
Every time gawk opens a new data file for processing, it sets
ARGIND to the index in ARGV of the file name. Thus, the
condition `FILENAME == ARGV[ARGIND]' is always true.
This variable is useful in file processing; it allows you to tell how far along you are in the list of data files, and to distinguish between multiple successive instances of the same filename on the command line.
While you can change the value of ARGIND within your awk
program, gawk will automatically set it to a new value when the
next file is opened.
This variable is a gawk extension; in other awk implementations
it is not special.
ENVIRON
ENVIRON["HOME"] might be `/u/close'. Changing this array
does not affect the environment passed on to any programs that
awk may spawn via redirection or the system function.
(In a future version of gawk, it may do so.)
Some operating systems may not have environment variables.
On such systems, the array ENVIRON is empty.
ERRNO
getline,
during a read for getline, or during a close operation,
then ERRNO will contain a string describing the error.
This variable is a gawk extension; in other awk implementations
it is not special.
FILENAME
awk is currently reading.
If awk is reading from the standard input (in other words,
there are no files listed on the command line),
FILENAME is set to "-".
FILENAME is changed each time a new file is read
(see section Reading Input Files).FNR
FNR is the current record number in the current file. FNR is
incremented each time a new record is read
(see section Explicit Input with getline). It is reinitialized
to 0 each time a new input file is started.NF
NF is the number of fields in the current input record.
NF is set each time a new record is read, when a new field is
created, or when $0 changes (see section Examining Fields).NR
awk has processed since
the beginning of the program's execution.
(see section How Input is Split into Records).
NR is set each time a new record is read.RLENGTH
RLENGTH is the length of the substring matched by the
match function
(see section Built-in Functions for String Manipulation).
RLENGTH is set by invoking the match function. Its value
is the length of the matched string, or -1 if no match was found.RSTART
RSTART is the start-index in characters of the substring matched by the
match function
(see section Built-in Functions for String Manipulation).
RSTART is set by invoking the match function. Its value
is the position of the string where the matched substring starts, or 0
if no match was found.
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