gawk - pattern scanning and processing language
gawk [ POSIX or GNU style options ] -f program-file [ -- ] file ... gawk [ POSIX or GNU style options ] [ -- ] program-text file ...
pgawk [ POSIX or GNU style options ] -f program-file [ -- ] file ... pgawk [ POSIX or GNU style options ] [ -- ] program-text file ...
Gawk is the GNU Project’s implementation of the AWK programming language. It conforms to the definition of the language in the POSIX 1003.2 Command Language And Utilities Standard. This version in turn is based on the description in The AWK Programming Language, by Aho, Kernighan, and Weinberger, with the additional features found in the System V Release 4 version of UNIX awk. Gawk also provides more recent Bell Laboratories awk extensions, and a number of GNU-specific extensions.
Pgawk is the profiling version of gawk. It is identical in every way to gawk, except that programs run more slowly, and it automatically produces an execution profile in the file awkprof.out when done. See the --profile option, below.
The command line consists of options to gawk itself, the AWK program text (if not supplied via the -f or --file options), and values to be made available in the ARGC and ARGV pre-defined AWK variables.
Gawk options may be either traditional POSIX one letter options, or GNU style long options. POSIX options start with a single “-", while long options start with “--". Long options are provided for both GNU-specific features and for POSIX-mandated features.
Following the POSIX standard, gawk-specific options are supplied via arguments to the -W option. Multiple -W options may be supplied Each -W option has a corresponding long option, as detailed below. Arguments to long options are either joined with the option by an = sign, with no intervening spaces, or they may be provided in the next command line argument. Long options may be abbreviated, as long as the abbreviation remains unique.
Gawk accepts the following options, listed alphabetically.
? \x escape sequences are not recognized.
? Only space and tab act as field separators when FS is set to a single space, newline does not.
? You cannot continue lines after ? and :.
? The synonym func for the keyword function is not recognized.
? The operators ** and **= cannot be used in place of ^ and ^=.
? The fflush() function is not available.
An AWK program consists of a sequence of pattern-action statements and
optional function definitions.
AWK variables are dynamic; they come into existence when they are first
used. Their values are either floating-point numbers or strings, or
both, depending upon how they are used. AWK also has one dimensional
arrays; arrays with multiple dimensions may be simulated. Several predefined
variables are set as a program runs; these will be described as
needed and summarized below.
Records
Normally, records are separated by newline characters. You can control
how records are separated by assigning values to the built-in variable
RS. If RS is any single character, that character separates records.
Otherwise, RS is a regular expression. Text in the input that matches
this regular expression separates the record. However, in
compatibility mode, only the first character of its string value is
used for separating records. If RS is set to the null string, then
records are separated by blank lines. When RS is set to the null
string, the newline character always acts as a field separator, in
addition to whatever value FS may have.
Fields
As each input record is read, gawk splits the record into fields, using
the value of the FS variable as the field separator. If FS is a single
character, fields are separated by that character. If FS is the null
string, then each individual character becomes a separate field. Otherwise,
FS is expected to be a full regular expression. In the special
case that FS is a single space, fields are separated by runs of spaces
and/or tabs and/or newlines. (But see the discussion of --posix,
below). NOTE: The value of IGNORECASE (see below) also affects how
fields are split when FS is a regular expression, and how records are
separated when RS is a regular expression.
If the FIELDWIDTHS variable is set to a space separated list of numbers,
each field is expected to have fixed width, and gawk splits up
the record using the specified widths. The value of FS is ignored.
Assigning a new value to FS overrides the use of FIELDWIDTHS, and
restores the default behavior.
Each field in the input record may be referenced by its position, $1,
$2, and so on. $0 is the whole record. Fields need not be referenced
by constants:
n = 5
print $n
prints the fifth field in the input record.
The variable NF is set to the total number of fields in the input
record.
References to non-existent fields (i.e. fields after $NF) produce the
null-string. However, assigning to a non-existent field (e.g., $(NF+2)
= 5) increases the value of NF, creates any intervening fields with the
null string as their value, and causes the value of $0 to be recomputed,
with the fields being separated by the value of OFS. References
to negative numbered fields cause a fatal error. Decrementing NF
causes the values of fields past the new value to be lost, and the
value of $0 to be recomputed, with the fields being separated by the
value of OFS.
Assigning a value to an existing field causes the whole record to be
rebuilt when $0 is referenced. Similarly, assigning a value to $0
causes the record to be resplit, creating new values for the fields.
Built-in Variables
Gawk’s built-in variables are:
AWK is a line-oriented language. The pattern comes first, and then the
action. Action statements are enclosed in { and }. Either the pattern
may be missing, or the action may be missing, but, of course, not both.
If the pattern is missing, the action is executed for every single
record of input. A missing action is equivalent to
{ print }
which prints the entire record.
Comments begin with the “#” character, and continue until the end of
the line. Blank lines may be used to separate statements. Normally, a
statement ends with a newline, however, this is not the case for lines
ending in a “,", {, ?, :, &&, or ||. Lines ending in do or else also
have their statements automatically continued on the following line.
In other cases, a line can be continued by ending it with a “\", in
which case the newline will be ignored.
Multiple statements may be put on one line by separating them with a
“;". This applies to both the statements within the action part of a
pattern-action pair (the usual case), and to the pattern-action statements
themselves.
Patterns
AWK patterns may be one of the following:
BEGIN
END
/regular expression/
relational expression
pattern && pattern
pattern || pattern
pattern ? pattern : pattern
(pattern)
! pattern
pattern1, pattern2
BEGIN and END are two special kinds of patterns which are not tested
against the input. The action parts of all BEGIN patterns are merged
as if all the statements had been written in a single BEGIN block.
They are executed before any of the input is read. Similarly, all the
END blocks are merged, and executed when all the input is exhausted (or
when an exit statement is executed). BEGIN and END patterns cannot be
combined with other patterns in pattern expressions. BEGIN and END
patterns cannot have missing action parts.
For /regular expression/ patterns, the associated statement is executed
for each input record that matches the regular expression. Regular
expressions are the same as those in egrep(1)
, and are summarized
below.
A relational expression may use any of the operators defined below in
the section on actions. These generally test whether certain fields
match certain regular expressions.
The &&, ||, and ! operators are logical AND, logical OR, and logical
NOT, respectively, as in C. They do short-circuit evaluation, also as
in C, and are used for combining more primitive pattern expressions.
As in most languages, parentheses may be used to change the order of
evaluation.
The ?: operator is like the same operator in C. If the first pattern
is true then the pattern used for testing is the second pattern, otherwise
it is the third. Only one of the second and third patterns is
evaluated.
The pattern1, pattern2 form of an expression is called a range pattern.
It matches all input records starting with a record that matches pat_tern1,
and continuing until a record that matches pattern2, inclusive.
It does not combine with any other sort of pattern expression.
Regular Expressions
Regular expressions are the extended kind found in egrep. They are
composed of characters as follows:
The escape sequences that are valid in string constants (see below) are also valid in regular expressions.
Character classes are a new feature introduced in the POSIX standard. A character class is a special notation for describing lists of characters that have a specific attribute, but where the actual characters themselves can vary from country to country and/or from character set to character set. For example, the notion of what is an alphabetic character differs in the USA and in France.
A character class is only valid in a regular expression inside the brackets of a character list. Character classes consist of [:, a keyword denoting the class, and :]. The character classes defined by the POSIX standard are:
[:alnum:] Alphanumeric characters.
[:alpha:] Alphabetic characters.
[:blank:] Space or tab characters.
[:cntrl:] Control characters.
[:digit:] Numeric characters.
[:graph:] Characters that are both printable and visible. (A space is printable, but not visible, while an a is both.)
[:lower:] Lower-case alphabetic characters.
[:print:] Printable characters (characters that are not control characters.)
[:punct:] Punctuation characters (characters that are not letter, digits, control characters, or space characters).
[:space:] Space characters (such as space, tab, and formfeed, to name a few).
[:upper:] Upper-case alphabetic characters.
[:xdigit:] Characters that are hexadecimal digits.
For example, before the POSIX standard, to match alphanumeric characters, you would have had to write /[A-Za-z0-9]/. If your character set had other alphabetic characters in it, this would not match them, and if your character set collated differently from ASCII, this might not even match the ASCII alphanumeric characters. With the POSIX character classes, you can write /[[:alnum:]]/, and this matches the alphabetic and numeric characters in your character set.
Two additional special sequences can appear in character lists. These apply to non-ASCII character sets, which can have single symbols (called collating elements) that are represented with more than one character, as well as several characters that are equivalent for col_lating, or sorting, purposes. (E.g., in French, a plain “e” and a grave-accented e‘ are equivalent.)
Collating Symbols
A collating symbol is a multi-character collating element
enclosed in [. and .]. For example, if ch is a collating element,
then [[.ch.]] is a regular expression that matches this
collating element, while [ch] is a regular expression that
matches either c or h.
Equivalence Classes
An equivalence class is a locale-specific name for a list of
characters that are equivalent. The name is enclosed in [= and
=]. For example, the name e might be used to represent all of
“e,” “e?,” and “e‘.” In this case, [[=e=]] is a regular expression
that matches any of e, e?, or e‘.
These features are very valuable in non-English speaking locales. The library functions that gawk uses for regular expression matching currently only recognize POSIX character classes; they do not recognize collating symbols or equivalence classes.
The \y, \B, \<, \>, \w, \W, \’, and \’ operators are specific to gawk; they are extensions based on facilities in the GNU regular expression libraries.
The various command line options control how gawk interprets characters in regular expressions.
No options
In the default case, gawk provide all the facilities of POSIX
regular expressions and the GNU regular expression operators
described above. However, interval expressions are not supported.
Actions
Action statements are enclosed in braces, { and }. Action statements
consist of the usual assignment, conditional, and looping statements
found in most languages. The operators, control statements, and
input/output statements available are patterned after those in C.
Operators
The operators in AWK, in order of decreasing precedence, are
Control Statements
The control statements are as follows:
if (condition) statement [ else statement ]
while (condition) statement
do statement while (condition)
for (expr1; expr2; expr3) statement
for (var in array) statement
break
continue
delete array[index]
delete array
exit [ expression ]
{ statements }
I/O Statements
The input/output statements are as follows:
close(file [, how]) Close file, pipe or co-process. The optional how should only be used when closing one end of a two-way pipe to a co-process. It must be a string value, either “to” or “from".
command | getline [var]
Run command piping the output either into $0 or
var, as above.
command |& getline [var]
Run command as a co-process piping the output
either into $0 or var, as above. Co-processes
are a gawk extension.
print expr-list >file Prints expressions on file. Each expression is separated by the value of the OFS variable. The output record is terminated with the value of the ORS variable.
printf fmt, expr-list Format and print.
printf fmt, expr-list >file
Format and print on file.
Additional output redirections are allowed for print and printf.
print ... >> file
appends output to the file.
print ... | command
writes on a pipe.
print ... |& command
sends data to a co-process.
The getline command returns 0 on end of file and -1 on an error. Upon an error, ERRNO contains a string describing the problem.
NOTE: If using a pipe or co-process to getline, or from print or printf within a loop, you must use close() to create new instances of the command. AWK does not automatically close pipes or co-processes when they return EOF.
The printf Statement
The AWK versions of the printf statement and sprintf() function (see
below) accept the following conversion specification formats:
%d, %i A decimal number (the integer part).
%e , %E
A floating point number of the form [-]d.dddddde[+-]dd. The %E
format uses E instead of e.
%g , %G
Use %e or %f conversion, whichever is shorter, with nonsignificant
zeros suppressed. The %G format uses %E instead of %e.
%x , %X
An unsigned hexadecimal number (an integer). The %X format
uses ABCDEF instead of abcdef.
NOTE: When using the integer format-control letters for values that are outside the range of a C long integer, gawk switches to the %g format specifier. If --lint is provided on the command line gawk warns about this. Other versions of awk may print invalid values or do something else entirely.
Optional, additional parameters may lie between the % and the control letter:
count$ Use the count’th argument at this point in the formatting. This is called a positional specifier and is intended primarily for use in translated versions of format strings, not in the original text of an AWK program. It is a gawk extension.
space For numeric conversions, prefix positive values with a space, and negative values with a minus sign.
width The field should be padded to this width. The field is normally padded with spaces. If the 0 flag has been used, it is padded with zeroes.
The dynamic width and prec capabilities of the ANSI C printf() routines are supported. A * in place of either the width or prec specifications causes their values to be taken from the argument list to printf or sprintf(). To use a positional specifier with a dynamic width or precision, supply the count$ after the * in the format string. For example, “%3$*2$.*1$s".
Special File Names
When doing I/O redirection from either print or printf into a file, or
via getline from a file, gawk recognizes certain special filenames
internally. These filenames allow access to open file descriptors
inherited from gawk’s parent process (usually the shell). These file
names may also be used on the command line to name data files. The
filenames are:
/dev/stdin The standard input.
/dev/stdout The standard output.
/dev/stderr The standard error output.
These are particularly useful for error messages. For example:
print “You blew it!” > “/dev/stderr"
whereas you would otherwise have to use
print “You blew it!” | “cat 1>&2"
The following special filenames may be used with the |& co-process operator for creating TCP/IP network connections.
/inet/tcp/lport/rhost/rport File for TCP/IP connection on local port lport to remote host rhost on remote port rport. Use a port of 0 to have the system pick a port.
/inet/udp/lport/rhost/rport Similar, but use UDP/IP instead of TCP/IP.
/inet/raw/lport/rhost/rport Reserved for future use.
Other special filenames provide access to information about the running gawk process. These filenames are now obsolete. Use the PROCINFO array to obtain the information they provide. The filenames are:
/dev/pgrpid Reading this file returns the process group ID of the current process, in decimal, terminated with a newline.
Numeric Functions
AWK has the following built-in arithmetic functions:
srand([expr]) Uses expr as a new seed for the random number generator. If no expr is provided, the time of day is used. The return value is the previous seed for the random number generator.
String Functions
Gawk has the following built-in string functions:
gensub(r, s, h [, t]) Search the target string t for matches of the regular expression r. If h is a string beginning with g or G, then replace all matches of r with s. Otherwise, h is a number indicating which match of r to replace. If t is not supplied, $0 is used instead. Within the replacement text s, the sequence \n, where n is a digit from 1 to 9, may be used to indicate just the text that matched the n’th parenthesized subexpression. The sequence \0 represents the entire matched text, as does the character &. Unlike sub() and gsub(), the modified string is returned as the result of the function, and the original target string is not changed.
sprintf(fmt, expr-list) Prints expr-list according to fmt, and returns the resulting string.
Time Functions
Since one of the primary uses of AWK programs is processing log files
that contain time stamp information, gawk provides the following functions
for obtaining time stamps and formatting them.
mktime(datespec)
Turns datespec into a time stamp of the same form as returned
by systime(). The datespec is a string of the form YYYY MM
DD HH MM SS[ DST]. The contents of the string are six or
seven numbers representing respectively the full year including
century, the month from 1 to 12, the day of the month
from 1 to 31, the hour of the day from 0 to 23, the minute
from 0 to 59, and the second from 0 to 60, and an optional
daylight saving flag. The values of these numbers need not
be within the ranges specified; for example, an hour of -1
means 1 hour before midnight. The origin-zero Gregorian calendar
is assumed, with year 0 preceding year 1 and year -1
preceding year 0. The time is assumed to be in the local
timezone. If the daylight saving flag is positive, the time
is assumed to be daylight saving time; if zero, the time is
assumed to be standard time; and if negative (the default),
mktime() attempts to determine whether daylight saving time
is in effect for the specified time. If datespec does not
contain enough elements or if the resulting time is out of
range, mktime() returns -1.
strftime([format [, timestamp]])
Formats timestamp according to the specification in format.
The timestamp should be of the same form as returned by systime().
If timestamp is missing, the current time of day is
used. If format is missing, a default format equivalent to
the output of date(1)
is used. See the specification for the
strftime() function in ANSI C for the format conversions that
are guaranteed to be available. A public-domain version of
strftime(3)
and a man page for it come with gawk; if that
version was used to build gawk, then all of the conversions
described in that man page are available to gawk.
systime() Returns the current time of day as the number of seconds since the Epoch (1970-01-01 00:00:00 UTC on POSIX systems).
Bit Manipulations Functions
Starting with version 3.1 of gawk, the following bit manipulation functions
are available. They work by converting double-precision floating
point values to unsigned long integers, doing the operation, and then
converting the result back to floating point. The functions are:
lshift(val, count) Return the value of val, shifted left by count bits.
rshift(val, count) Return the value of val, shifted right by count bits.
Internationalization Functions
Starting with version 3.1 of gawk, the following functions may be used
from within your AWK program for translating strings at run-time. For
full details, see GAWK: Effective AWK Programming.
bindtextdomain(directory [, domain])
Specifies the directory where gawk looks for the .mo files, in
case they will not or cannot be placed in the ‘’standard’’ locations
(e.g., during testing). It returns the directory where
domain is ‘’bound.’’
The default domain is the value of TEXTDOMAIN. If directory is
the null string (""), then bindtextdomain() returns the current
binding for the given domain.
dcgettext(string [, domain [, category]])
Returns the translation of string in text domain domain for
locale category category. The default value for domain is the
current value of TEXTDOMAIN. The default value for category is
“LC_MESSAGES".
If you supply a value for category, it must be a string equal to
one of the known locale categories described in GAWK: Effective
AWK Programming. You must also supply a text domain. Use
TEXTDOMAIN if you want to use the current domain.
dcngettext(string1 , string2 , number [, domain [, category]]) Returns the plural form used for number of the translation of string1 and string2 in text domain domain for locale category category. The default value for domain is the current value of TEXTDOMAIN. The default value for category is “LC_MESSAGES". If you supply a value for category, it must be a string equal to one of the known locale categories described in GAWK: Effective AWK Programming. You must also supply a text domain. Use TEXTDOMAIN if you want to use the current domain.
Functions in AWK are defined as follows:
function name(parameter list) { statements }
Functions are executed when they are called from within expressions in either patterns or actions. Actual parameters supplied in the function call are used to instantiate the formal parameters declared in the function. Arrays are passed by reference, other variables are passed by value.
Since functions were not originally part of the AWK language, the provision for local variables is rather clumsy: They are declared as extra parameters in the parameter list. The convention is to separate local variables from real parameters by extra spaces in the parameter list. For example:
function f(p, q, a, b) # a and b are local
{
...
}
The left parenthesis in a function call is required to immediately follow the function name, without any intervening white space. This is to avoid a syntactic ambiguity with the concatenation operator. This restriction does not apply to the built-in functions listed above.
Functions may call each other and may be recursive. Function parameters used as local variables are initialized to the null string and the number zero upon function invocation.
Use return expr to return a value from a function. The return value is undefined if no value is provided, or if the function returns by “falling off” the end.
If --lint has been provided, gawk warns about calls to undefined functions at parse time, instead of at run time. Calling an undefined function at run time is a fatal error.
The word func may be used in place of function.
Beginning with version 3.1 of gawk, you can dynamically add new builtin functions to the running gawk interpreter. The full details are beyond the scope of this manual page; see GAWK: Effective AWK Program_ming for the details.
extension(object, function)
Dynamically link the shared object file named by object, and
invoke function in that object, to perform initialization.
These should both be provided as strings. Returns the value
returned by function.
This function is provided and documented in GAWK: Effective AWK Pro_gramming, but everything about this feature is likely to change in the next release. We STRONGLY recommend that you do not use this feature for anything that you aren’t willing to redo.
pgawk accepts two signals. SIGUSR1 causes it to dump a profile and function call stack to the profile file, which is either awkprof.out, or whatever file was named with the --profile option. It then continues to run. SIGHUP causes it to dump the profile and function call stack and then exit.
Print and sort the login names of all users:
Count lines in a file:
{ nlines++ }
END { print nlines }
Precede each line by its number in the file:
{ print FNR, $0 }
Concatenate and line number (a variation on a theme):
{ print NR, $0 }
Run an external command for particular lines of data:
tail -f access_log
awk ‘/myhome.html/ { system("nmap “ $1 “>> logdir/myhome.html") }’
String constants are sequences of characters enclosed in double quotes. In non-English speaking environments, it is possible to mark strings in the AWK program as requiring translation to the native natural language. Such strings are marked in the AWK program with a leading underscore ("_"). For example,
gawk ‘BEGIN { print “hello, world” }’
always prints hello, world. But,
gawk ‘BEGIN { print _"hello, world” }’
might print bonjour, monde in France.
There are several steps involved in producing and running a localizable AWK program.
1. Add a BEGIN action to assign a value to the TEXTDOMAIN variable to set the text domain to a name associated with your program.
BEGIN { TEXTDOMAIN = “myprog” }
This allows gawk to find the .mo file associated with your program. Without this step, gawk uses the messages text domain, which likely does not contain translations for your program.
2. Mark all strings that should be translated with leading underscores.
3. If necessary, use the dcgettext() and/or bindtextdomain() functions in your program, as appropriate.
4. Run gawk --gen-po -f myprog.awk > myprog.po to generate a .po file for your program.
5. Provide appropriate translations, and build and install a corresponding .mo file.
The internationalization features are described in full detail in GAWK: Effective AWK Programming.
A primary goal for gawk is compatibility with the POSIX standard, as well as with the latest version of UNIX awk. To this end, gawk incorporates the following user visible features which are not described in the AWK book, but are part of the Bell Laboratories version of awk, and are in the POSIX standard.
The book indicates that command line variable assignment happens when awk would otherwise open the argument as a file, which is after the BEGIN block is executed. However, in earlier implementations, when such an assignment appeared before any file names, the assignment would happen before the BEGIN block was run. Applications came to depend on this “feature.” When awk was changed to match its documentation, the -v option for assigning variables before program execution was added to accommodate applications that depended upon the old behavior. (This feature was agreed upon by both the Bell Laboratories and the GNU developers.)
The -W option for implementation specific features is from the POSIX standard.
When processing arguments, gawk uses the special option “--” to signal the end of arguments. In compatibility mode, it warns about but otherwise ignores undefined options. In normal operation, such arguments are passed on to the AWK program for it to process.
The AWK book does not define the return value of srand(). The POSIX standard has it return the seed it was using, to allow keeping track of random number sequences. Therefore srand() in gawk also returns its current seed.
Other new features are: The use of multiple -f options (from MKS awk); the ENVIRON array; the \a, and \v escape sequences (done originally in gawk and fed back into the Bell Laboratories version); the tolower() and toupper() built-in functions (from the Bell Laboratories version); and the ANSI C conversion specifications in printf (done first in the Bell Laboratories version).
There are two features of historical AWK implementations that gawk supports. First, it is possible to call the length() built-in function not only with no argument, but even without parentheses! Thus,
is the same as either of
a = length()
a = length($0)
This feature is marked as “deprecated” in the POSIX standard, and gawk issues a warning about its use if --lint is specified on the command line.
The other feature is the use of either the continue or the break statements outside the body of a while, for, or do loop. Traditional AWK implementations have treated such usage as equivalent to the next statement. Gawk supports this usage if --traditional has been specified.
Gawk has a number of extensions to POSIX awk. They are described in this section. All the extensions described here can be disabled by invoking gawk with the --traditional option.
The following features of gawk are not available in POSIX awk.
? No path search is performed for files named via the -f option. Therefore the AWKPATH environment variable is not special.
? The \x escape sequence. (Disabled with --posix.)
? The fflush() function. (Disabled with --posix.)
? The ability to continue lines after ? and :. (Disabled with --posix.)
? Octal and hexadecimal constants in AWK programs.
? The ARGIND, BINMODE, ERRNO, LINT, RT and TEXTDOMAIN variables are not special.
? The IGNORECASE variable and its side-effects are not available.
? The FIELDWIDTHS variable and fixed-width field splitting.
? The PROCINFO array is not available.
? The use of RS as a regular expression.
? The special file names available for I/O redirection are not recognized.
? The |& operator for creating co-processes.
? The ability to split out individual characters using the null string as the value of FS, and as the third argument to split().
? The optional second argument to the close() function.
? The optional third argument to the match() function.
? The ability to use positional specifiers with printf and sprintf().
? The use of delete array to delete the entire contents of an array.
? The use of nextfile to abandon processing of the current input file.
? The and(), asort(), asorti(), bindtextdomain(), compl(), dcgettext(), dcngettext(), gensub(), lshift(), mktime(), or(), rshift(), strftime(), strtonum(), systime() and xor() functions.
? Localizable strings.
? Adding new built-in functions dynamically with the extension() function.
The AWK book does not define the return value of the close() function. Gawk’s close() returns the value from fclose(3) , or pclose(3) , when closing an output file or pipe, respectively. It returns the process’s exit status when closing an input pipe. The return value is -1 if the named file, pipe or co-process was not opened with a redirection.
When gawk is invoked with the --traditional option, if the fs argument to the -F option is “t", then FS is set to the tab character. Note that typing gawk -F\t ... simply causes the shell to quote the “t,", and does not pass “\t” to the -F option. Since this is a rather ugly special case, it is not the default behavior. This behavior also does not occur if --posix has been specified. To really get a tab character as the field separator, it is best to use single quotes: gawk -F’\t’ ....
If gawk is configured with the --enable-switch option to the configure
command, then it accepts an additional control-flow statement:
switch (expression) {
case value|regex : statement
...
[ default: statement ]
}
The AWKPATH environment variable can be used to provide a list of directories that gawk searches when looking for files named via the -f and --file options.
If POSIXLY_CORRECT exists in the environment, then gawk behaves exactly as if --posix had been specified on the command line. If --lint has been specified, gawk issues a warning message to this effect.
egrep(1) , getpid(2) , getppid(2) , getpgrp(2) , getuid(2) , geteuid(2) , getgid(2) , getegid(2) , getgroups(2)
The AWK Programming Language, Alfred V. Aho, Brian W. Kernighan, Peter J. Weinberger, Addison-Wesley, 1988. ISBN 0-201-07981-X.
GAWK: Effective AWK Programming, Edition 3.0, published by the Free Software Foundation, 2001.
The -F option is not necessary given the command line variable assignment feature; it remains only for backwards compatibility.
Syntactically invalid single character programs tend to overflow the parse stack, generating a rather unhelpful message. Such programs are surprisingly difficult to diagnose in the completely general case, and the effort to do so really is not worth it.
The original version of UNIX awk was designed and implemented by Alfred Aho, Peter Weinberger, and Brian Kernighan of Bell Laboratories. Brian Kernighan continues to maintain and enhance it.
Paul Rubin and Jay Fenlason, of the Free Software Foundation, wrote gawk, to be compatible with the original version of awk distributed in Seventh Edition UNIX. John Woods contributed a number of bug fixes. David Trueman, with contributions from Arnold Robbins, made gawk compatible with the new version of UNIX awk. Arnold Robbins is the current maintainer.
The initial DOS port was done by Conrad Kwok and Scott Garfinkle. Scott Deifik is the current DOS maintainer. Pat Rankin did the port to VMS, and Michal Jaegermann did the port to the Atari ST. The port to OS/2 was done by Kai Uwe Rommel, with contributions and help from Darrel Hankerson. Fred Fish supplied support for the Amiga, Stephen Davies provided the Tandem port, and Martin Brown provided the BeOS port.
This man page documents gawk, version 3.1.5.
If you find a bug in gawk, please send electronic mail to buggawk@gnu.org. Please include your operating system and its revision, the version of gawk (from gawk --version), what C compiler you used to compile it, and a test program and data that are as small as possible for reproducing the problem.
Before sending a bug report, please do two things. First, verify that you have the latest version of gawk. Many bugs (usually subtle ones) are fixed at each release, and if yours is out of date, the problem may already have been solved. Second, please read this man page and the reference manual carefully to be sure that what you think is a bug really is, instead of just a quirk in the language.
Whatever you do, do NOT post a bug report in comp.lang.awk. While the gawk developers occasionally read this newsgroup, posting bug reports there is an unreliable way to report bugs. Instead, please use the electronic mail addresses given above.
If you’re using a GNU/Linux system or BSD-based system, you may wish to submit a bug report to the vendor of your distribution. That’s fine, but please send a copy to the official email address as well, since there’s no guarantee that the bug will be forwarded to the gawk maintainer.
Brian Kernighan of Bell Laboratories provided valuable assistance during testing and debugging. We thank him.
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