Man Page For Os X Awk
Ldfps loads the hardware floating point status register with fps. See the PDP-11 hardware handbook for a description of the meaning of the various bits in fps. BUGS Ldfps is unique to the PDP-11 and 2BSD; its use is discouraged. This compiles without change on Macintosh OS X using gcc and the standard developer tools. The version of malloc that comes with some systems is sometimes astonishly slow. If awk seems slow, you might try fixing that. More generally, turning on optimization can significantly improve awk's speed, perhaps by 1/3 for highest levels. A Note About.
Name
gawk - pattern scanning and processing language
Synopsis
gawk [ POSIX or GNU style options ] -fprogram-file [ -- ] file ..
gawk [ POSIX or GNU style options ] [ -- ] program-text file ..
pgawk [ POSIX or GNU style options ] -fprogram-file [ -- ] file ..
pgawk [ POSIX or GNU style options ] [ -- ] program-text file ..
Description
Gawk is the GNU Project's implementation of the AWK programming language. It conforms to the definition of the languagein the POSIX 1003.1 Standard. This version in turn is based on the description in The AWK Programming Language, by Aho, Kernighan, andWeinberger, with the additional features found in the System V Release 4 version of UNIXawk. Gawk also provides more recent BellLaboratories 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 itautomatically 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 --fileoptions), and values to be made available in the ARGC and ARGV pre-defined AWK variables.
Option Format
Gawk options may be either traditional POSIX one letter options, or GNU -style long options. POSIXoptions start with a single '-', while long options start with '--'. Long options are provided for both GNU -specific features and forPOSIX -mandated features.
Following the POSIX standard, gawk-specific options are supplied via arguments to the -W option. Multiple -W options maybe 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 theabbreviation remains unique.
Options
Gawk accepts the following options, listed by frequency.
Having a list of all the global variables is a good way to look for typographical errors in your programs. You would also use this option if you have a largeprogram with a lot of functions, and you want to be sure that your functions don't inadvertently use global variables that you meant to be local. (This is aparticularly easy mistake to make with simple variable names like i, j, and so on.)
• 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.
Signal the end of options. This is useful to allow further arguments to the AWK program itself to start with a '-'. This provides consistencywith the argument parsing convention used by most other POSIX programs.
Awk Program Execution
An AWK program consists of a sequence of pattern-action statements and optional function definitions.
pattern{action statements}
The environment variable AWKPATH specifies a search path to use when finding source files named with the -f option. If this variable does notexist, the default path is '.:/usr/local/share/awk'. (The actual directory may vary, depending upon how gawk was built and installed.) If a filename given to the -f option contains a '/' character, no path search is performed.
Gawk executes AWK programs in the following order. First, all variable assignments specified via the -v option are performed.Next, gawk compiles the program into an internal form. Then, gawk executes the code in the BEGINblock(s) (if any), and then proceeds toread each file named in the ARGV array. If there are no files named on the command line, gawk reads the standard input.
If a filename on the command line has the form var=val it is treated as a variable assignment. The variable var will be assignedthe value val. (This happens after any BEGINblock(s) have been run.) Command line variable assignment is most useful for dynamically assigningvalues to the variables AWK uses to control how input is broken into fields and records. It is also useful for controlling state if multiplepasses are needed over a single data file.
If the value of a particular element of ARGV is empty ('), gawk skips over it.
For each record in the input, gawk tests to see if it matches any pattern in the AWK program. For each pattern that the recordmatches, the associated action is executed. The patterns are tested in the order they occur in the program.
Finally, after all the input is exhausted, gawk executes the code in the ENDblock(s) (if any).
VARIABLES, RECORDS AND FIELDS
AWK variables are dynamic; they come into existence when they are first used. Their values are either floating-point numbers or strings, orboth, depending upon how they are used. AWK also has one dimensional arrays; arrays with multiple dimensions may be simulated. Severalpre-defined variables are set as a program runs; these are described as needed and summarized below.
Records
The number of command line arguments (does not include options to gawk, or the program source).
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. Dynamically changing the contents of ARGV can control the files usedfor data.
BINMODE
On non-POSIX systems, specifies use of 'binary' mode for all file I/O. 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. Any other string value is treated as 'rw', but generates awarning message.
CONVFMT
The conversion format for numbers, '%.6g', by default.
ENVIRON
An array containing the values of the current environment. The array is indexed by the environment variables, each element being the value of that variable(e.g., ENVIRON['HOME'] might be /home/arnold). Changing this array does not affect the environment seen by programs which gawk spawns viaredirection or the system() function.
ERRNO
If a system error occurs either doing a redirection for getline, during a read for getline, or during a close(), then ERRNO willcontain a string describing the error. The value is subject to translation in non-English locales.
FIELDWIDTHS
A white-space separated list of fieldwidths. When set, gawk parses the input into fields of fixed width, instead of using the value of the FSvariable as the field separator.
FILENAME
The name of the current input file. If no files are specified on the command line, the value of FILENAME is '-'. However, FILENAME isundefined inside the BEGIN block (unless set by getline).
FNR
The input record number in the current input file.
FS
The input field separator, a space by default. See Fields, above.
IGNORECASE
Controls the case-sensitivity of all regular expression and string operations. If IGNORECASE has a non-zero value, then string comparisons andpattern matching in rules, field splitting with FS, record separating with RS, regular expression matching with ~ and !~, and thegensub(), gsub(), index(), match(), split(), and sub() built-in functions all ignore case when doing regularexpression operations. NOTE: Array subscripting is not affected. However, the asort() and asorti() functions are affected.
Provides dynamic control of the --lint option from within an AWK program. When true, gawk prints lint warnings. When false, itdoes not. When assigned the string value 'fatal', lint warnings become fatal errors, exactly like --lint=fatal. Any other true value just printswarnings.
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
The elements of this array provide access to information about the running AWK program. On some systems, there may be elements in the array,'group1' through 'groupn' for some n, which is the number of supplementary groups that the process has. Use the inoperator to test for these elements. The following elements are guaranteed to be available:
PROCINFO['egid']the value of the getegid(2) system call.
PROCINFO['euid']
the value of the geteuid(2) system call.
PROCINFO['FS']
'FS' if field splitting with FS is in effect, or 'FIELDWIDTHS' if field splitting with FIELDWIDTHS is in effect.
PROCINFO['gid']
the value of the getgid(2) system call.
PROCINFO['pgrpid']
the process group ID of the current process.
PROCINFO['pid']
the process ID of the current process.
PROCINFO['ppid']
the parent process ID of the current process.
PROCINFO['uid']
the value of the getuid(2) system call.
The version of gawk. This is available from version 3.1.4 and later.
RSThe input record separator, by default a newline.
RT
The record terminator. Gawk sets RT to the input text that matched the character or regular expression specified by RS.
RSTART
The index of the first character matched by match(); 0 if no match. (This implies that character indices start at one.)
RLENGTH
The length of the string matched by match(); -1 if no match.
SUBSEP
The character used to separate multiple subscripts in array elements, by default '034'.
TEXTDOMAIN
The text domain of the AWK program; used to find the localized translations for the program's strings.
Arrays
x[i, j, k] = 'hello, worldn'
The special operator in may be used to test if an array has an index consisting of a particular value.
The in construct may also be used in a for loop to iterate over all the elements of an array.
An element may be deleted from an array using the delete statement. The delete statement may also be used to delete the entire contents of anarray, just by specifying the array name without a subscript.
Variable Typing And Conversion
Variables and fields may be (floating point) numbers, or strings, or both. How the value of a variable is interpreted depends upon its context. If used in anumeric expression, it will be treated as a number; if used as a string it will be treated as a string.To force a variable to be treated as a number, add 0 to it; to force it to be treated as a string, concatenate it with the null string.
When a string must be converted to a number, the conversion is accomplished using strtod(3). A number is converted to a string by using the value ofCONVFMT as a format string for sprintf(3), with the numeric value of the variable as the argument. However, even though all numbers inAWK are floating-point, integral values are always converted as integers. Thus, given
the variable b has a string value of '12' and not '12.00'.When operating in POSIX mode (such as with the --posix command line option), beware that locale settings may interfere with the way decimal numbersare treated: the decimal separator of the numbers you are feeding to gawk must conform to what your locale would expect, be it a comma (,) or a period(.).
Gawk performs comparisons as follows: If two variables are numeric, they are compared numerically. If one value is numeric and the other has a stringvalue that is a 'numeric string,' then comparisons are also done numerically. Otherwise, the numeric value is converted to a string and a string comparison isperformed. Two strings are compared, of course, as strings.
Note that string constants, such as '57', are not numeric strings, they are string constants. The idea of 'numeric string' only applies tofields, getline input, FILENAME, ARGV elements, ENVIRON elements and the elements of an array created by split() that arenumeric strings. The basic idea is that user input, and only user input, that looks numeric, should be treated that way.
Uninitialized variables have the numeric value 0 and the string value ' (the null, or empty, string).
Octal and Hexadecimal Constants
A literal backslash.
a
The 'alert' character; usually the ASCII BEL character.
b
backspace.
f
form-feed.
n
newline.
r
carriage return.
t
horizontal tab.
v
vertical tab.
The character represented by the 1-, 2-, or 3-digit sequence of octal digits. E.g., '033' is the ASCII ESC (escape) character.
c
The literal character c.
The escape sequences may also be used inside constant regular expressions (e.g., /[ tfnrv]/ matches whitespace characters).In compatibility mode, the characters represented by octal and hexadecimal escape sequences are treated literally when used in regular expression constants.Thus, /a52b/ is equivalent to /a*b/.
Patterns And Actions
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 singlerecord of input. A missing action is equivalent to
Comments begin with the '#' character, and continue until the end of the line. Blank lines may be used to separate statements. Normally, a statement endswith a newline, however, this is not the case for lines ending in a ',', {, ?, :, &&, or . Lines ending indo 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-actionpair (the usual case), and to the pattern-action statements themselves.
Patterns
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 matchcertain regular expressions.
The &&, , and ! operators are logical AND, logical OR, and logical NOT, respectively, as in C. They do short-circuitevaluation, 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 ofevaluation.
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 isthe 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 thatmatches pattern1, and continuing until a record that matches pattern2, inclusive. It does not combine with any other sort of patternexpression.
Regular Expressions
matches the non-metacharacter c.
c
matches the literal character c.
.
matches any character including newline.
^
matches the beginning of a string.
$
matches the end of a string.
[abc..]
character list, matches any of the characters abc...
[^abc..]
negated character list, matches any character except abc...
r1r2
alternation: matches either r1 or r2.
r1r2
concatenation: matches r1, and then r2.
r+
matches one or more r's.
r*
matches zero or more r's.
r?
matches zero or one r's.
(r)
grouping: matches r.
r{n}
r{n,}
r{n,m}
One or two numbers inside braces denote an interval expression. If there is one number in the braces, the preceding regular expression r isrepeated n times. If there are two numbers separated by a comma, r is repeated n to m times. If there is one number followed by acomma, then r is repeated at least n times.
matches the empty string at either the beginning or the end of a word.
B
matches the empty string within a word.
<
matches the empty string at the beginning of a word.
>
matches the empty string at the end of a word.
w
matches any word-constituent character (letter, digit, or underscore).
W
matches any character that is not word-constituent.
'
matches the empty string at the beginning of a buffer (string).
'
matches the empty string at the end of a buffer.
The escape sequences that are valid in string constants (see below) are also valid in regular expressions.Character classes are a feature introduced in the POSIX standard. A character class is a special notation for describing lists ofcharacters that have a specific attribute, but where the actual characters themselves can vary from country to country and/or from character set to characterset. 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 keyworddenoting 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:]
Os X 10.12
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 characterset had other alphabetic characters in it, this would not match them, and if your character set collated differently from ASCII , this might noteven match the ASCII alphanumeric characters. With the POSIX character classes, you can write /[[:alnum:]]/, and thismatches the alphabetic and numeric characters in your character set, no matter what it is.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 collating,or sorting, purposes. (E.g., in French, a plain 'e' and a grave-accented '`' are equivalent.)
The y, B, <, >, w, W, ', and ' operators are specific to gawk; they areextensions based on facilities in the GNU regular expression libraries.
The various command line options control how gawk interprets characters in regular expressions.
Actions
- The control statements are as follows:
I/O Statements
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 stringvalue, either 'to' or 'from'.
getline
Set $0 from next input record; set NF, NR, FNR.
getline <file
Set $0 from next record of file; set NF.
getlinevar
Set var from next input record; set NR, FNR.
getlinevar<file
Set var from next record of file.
Run command piping the output either into $0 or var, as above.
Optional, additional parameters may lie between the % and the control letter:
count$Use the count'th argument at this point in the formatting. This is called a positional specifier and is intended primarily for use intranslated versions of format strings, not in the original text of an AWK program. It is a gawk extension.
-
The expression should be left-justified within its field.
space
For numeric conversions, prefix positive values with a space, and negative values with a minus sign.
+
The plus sign, used before the width modifier (see below), says to always supply a sign for numeric conversions, even if the data to be formatted ispositive. The + overrides the space modifier.
#
Use an 'alternate form' for certain control letters. For %o, supply a leading zero. For %x, and %X, supply a leading 0x or0X for a nonzero result. For %e, %E, %f and %F, the result always contains a decimal point. For %g, and %G,trailing zeros are not removed from the result.
0
A leading 0 (zero) acts as a flag, that indicates output should be padded with zeroes instead of spaces. This applies even to non-numeric outputformats. This flag only has an effect when the field width is wider than the value to be printed.
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.
.prec
A number that specifies the precision to use when printing. For the %e, %E, %f and %F, formats, this specifies the number ofdigits you want printed to the right of the decimal point. For the %g, and %G formats, it specifies the maximum number of significant digits. Forthe %d, %o, %i, %u, %x, and %X formats, it specifies the minimum number of digits to print. For %s, itspecifies the maximum number of characters from the string that should be printed.
Special File Names
The standard input.
/dev/stdout
The standard output.
/dev/stderr
The standard error output.
/dev/fd/n
The file associated with the open file descriptor n.
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 systempick 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.
Reading this file returns the process ID of the current process, in decimal, terminated with a newline.
/dev/ppid
Reading this file returns the parent process ID of the current process, in decimal, terminated with a newline.
/dev/pgrpid
Reading this file returns the process group ID of the current process, in decimal, terminated with a newline.
/dev/user
Reading this file returns a single record terminated with a newline. The fields are separated with spaces. $1 is the value of the getuid(2)system call, $2 is the value of the geteuid(2) system call, $3 is the value of the getgid(2) system call, and $4 is thevalue of the getegid(2) system call. If there are any additional fields, they are the group IDs returned by getgroups(2). Multiple groups may notbe supported on all systems.
Numeric Functions
Returns the arctangent of y/x in radians.
cos(expr)
Returns the cosine of expr, which is in radians.
exp(expr)
The exponential function.
int(expr)
Truncates to integer.
log(expr)
The natural logarithm function.
rand()
Returns a random number N, between 0 and 1, such that 0 ≤ N < 1.
sin(expr)
Returns the sine of expr, which is in radians.
sqrt(expr)
The square root function.
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 previousseed for the random number generator.
String Functions
Returns the number of elements in the source array s. The contents of s are sorted using gawk's normal rules for comparing values, andthe indices of the sorted values of s are replaced with sequential integers starting with 1. If the optional destination array d is specified,then s is first duplicated into d, and then d is sorted, leaving the indices of the source array s unchanged.
asorti(s [,d])
Returns the number of elements in the source array s. The behavior is the same as that of asort(), except that the array indices areused for sorting, not the array values. When done, the array is indexed numerically, and the values are those of the original indices. The original values arelost; thus provide a second array if you wish to preserve the original.
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 replaceall matches of r with s. Otherwise, h is a number indicating which match of r to replace. If t is not supplied, $0 isused 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 textthat matched the n'th parenthesized subexpression. The sequence 0 represents the entire matched text, as does the character &. Unlikesub() and gsub(), the modified string is returned as the result of the function, and the original target string is not changed.
gsub(r,s [,t])
For each substring matching the regular expression r in the string t, substitute the string s, and return the number of substitutions.If t is not supplied, use $0. An & in the replacement text is replaced with the text that was actually matched. Use & toget a literal &. (This must be typed as '&'; see GAWK: Effective AWK Programming for a fuller discussion of the rules for&'s and backslashes in the replacement text of sub(), gsub(), and gensub().)
index(s,t)
Returns the index of the string t in the string s, or 0 if t is not present. (This implies that character indices start at one.)
length([s])
Returns the length of the string s, or the length of $0 if s is not supplied. Starting with version 3.1.5, as a non-standard extension,with an array argument, length() returns the number of elements in the array.
match(s,r [,a])
Returns the position in s where the regular expression r occurs, or 0 if r is not present, and sets the values of RSTART andRLENGTH. Note that the argument order is the same as for the ~ operator: str~re. If array a is provided, ais cleared and then elements 1 through n are filled with the portions of s that match the corresponding parenthesized subexpression in r.The 0'th element of a contains the portion of s matched by the entire regular expression r. Subscripts a[n, 'start'],and a[n, 'length'] provide the starting index in the string and length respectively, of each matching substring.
split(s,a [,r])
Splits the string s into the array a on the regular expression r, and returns the number of fields. If r is omitted, FSis used instead. The array a is cleared first. Splitting behaves identically to field splitting, described above.
sprintf(fmt,expr-list)
Prints expr-list according to fmt, and returns the resulting string.
strtonum(str)
Examines str, and returns its numeric value. If str begins with a leading 0, strtonum() assumes that str is an octalnumber. If str begins with a leading 0x or 0X, strtonum() assumes that str is a hexadecimal number.
sub(r,s [,t])
Just like gsub(), but only the first matching substring is replaced.
substr(s,i [,n])
Returns the at most n-character substring of s starting at i. If n is omitted, the rest of s is used.
tolower(str)
Returns a copy of the string str, with all the upper-case characters in str translated to their corresponding lower-case counterparts.Non-alphabetic characters are left unchanged.
toupper(str)
Returns a copy of the string str, with all the lower-case characters in str translated to their corresponding upper-case counterparts.Non-alphabetic characters are left unchanged.
Time Functions
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
Return the bitwise AND of the values provided by v1 and v2.
compl(val)
Return the bitwise complement of val.
lshift(val,count)
Return the value of val, shifted left by count bits.
or(v1,v2)
Return the bitwise OR of the values provided by v1 and v2.
rshift(val,count)
Return the value of val, shifted right by count bits.
xor(v1,v2)
Return the bitwise XOR of the values provided by v1 and v2.
Internationalization Functions
The default domain is the value of TEXTDOMAIN. If directory is the null string ('), then bindtextdomain() returns thecurrent binding for the given domain.
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.
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.
User-defined Functions
Functions in AWK are defined as follows:
Since functions were not originally part of the AWK language, the provision for local variables is rather clumsy: They are declared as extraparameters in the parameter list. The convention is to separate local variables from real parameters by extra spaces in the parameter list. Forexample:
function f(p, q, a, b)# a and b are local
{ .. ; f(1, 2) ; .. }
The left parenthesis in a function call is required to immediately follow the function name, without any intervening white space. This avoids a syntacticambiguity 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 uponfunction invocation.
Use returnexpr 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 undefinedfunction at run time is a fatal error.
The word func may be used in place of function.
Dynamically Loading New Functions
Beginning with version 3.1 of gawk, you can dynamically add new built-in functions to the running gawk interpreter. The full details arebeyond the scope of this manual page; see GAWK: Effective AWK Programming for the details.
Signals
pgawk accepts two signals. SIGUSR1 causes it to dump a profile and function call stack to the profile file, which is eitherawkprof.out, or whatever file was named with the --profile option. It then continues to run. SIGHUP causes pgawk to dump theprofile and function call stack and then exit.
Examples
BEGIN{ FS = ':' }
{ print $1 'sort' }
- Precede each line by its number in the file:
{ print FNR, $0 }
- Run an external command for particular lines of data:
tail -f access_log
awk '/myhome.html/ { system('nmap ' $1 '>> logdir/myhome.html') }'
Internationalization
String constants are sequences of characters enclosed in double quotes. In non-English speaking environments, it is possible to mark strings in theAWK program as requiring translation to the native natural language. Such strings are marked in the AWK program with a leadingunderscore ('_'). For example,
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.
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 the corresponding .mo files.
Posix Compatibility
A primary goal for gawk is compatibility with the POSIX standard, as well as with the latest version of UNIXawk. To this end, gawk incorporates the following user visible features which are not described in the AWK book, but are part ofthe 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 theBEGIN block is executed. However, in earlier implementations, when such an assignment appeared before any file names, the assignment would happenbefore 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 wasagreed 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 otherwiseignores 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, toallow 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 BellLaboratories version); and the ANSI C conversion specifications in printf (done first in the Bell Laboratories version).
Historical Features
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,
a = length# Holy Algol 60, Batman!
a = length($0)
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.
Gnu Extensions
Gawk has a number of extensions to POSIXawk. They are described in this section. All the extensions described here can bedisabled by invoking gawk with the --traditional or --posix options.
The following features of gawk are not available in POSIXawk.
• 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.
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• 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 ability to pass an array to length().
• The use of deletearray to delete the entire contents of an array.
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• 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 fromfclose(3), or pclose(3), when closing an output file or pipe, respectively. It returns the process's exit status when closing an input pipe. Thereturn 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 tabcharacter. Note that typing gawk -Ft .. simply causes the shell to quote the 't,' and does not pass 't' to the -F option. Since this is arather 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 characteras 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-flowstatement:
Environment Variables
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.
See Also
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 current version of this document is availableonline at http://www.gnu.org/software/gawk/manual.
Bugs
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 surprisinglydifficult to diagnose in the completely general case, and the effort to do so really is not worth it.
Authors
The original version of UNIXawk was designed and implemented by Alfred Aho, Peter Weinberger, and Brian Kernighan of BellLaboratories. 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 inSeventh Edition UNIX . John Woods contributed a number of bug fixes. David Trueman, with contributions from Arnold Robbins, made gawkcompatible with the new version of UNIXawk. 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 MichalJaegermann 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. Andreas Buening nowmaintains the OS/2 port. Fred Fish supplied support for the Amiga, and Martin Brown provided the BeOS port. Stephen Davies provided the original Tandem port,and Matthew Woehlke provided changes for Tandem's POSIX-compliant systems. Ralf Wildenhues now maintains that port.
See the README file in the gawk distribution for current information about maintainers and which ports are currentlysupported.
Version Information
This man page documents gawk, version 3.1.7.
Bug Reports
If you find a bug in gawk, please send electronic mail to [email protected]. Please include your operating system and its revision, the versionof 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 reproducingthe problem.
Before sending a bug report, please do the following 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 see if setting the environment variableLC_ALL to LC_ALL=C causes things to behave as you expect. If so, it's a locale issue, and may or may not really be a bug. Finally, please readthis 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 bugreports 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 senda copy to the official email address as well, since there's no guarantee that the bug will be forwarded to the gawk maintainer.
Acknowledgements
Brian Kernighan of Bell Laboratories provided valuable assistance during testing and debugging. We thank him.
Copying Permissions
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Permission is granted to copy and distribute translations of this manual page into another language, under the above conditions for modified versions,except that this permission notice may be stated in a translation approved by the Foundation.