awk [OPTIONS] [PROGRAM] [FILE]
-F fs
--field-separator fs
Use fs for the input field separator (the value of the FS predefined variable).
-v var=val
--assign var=val
Assign the value val to the variable var, before execution of the program begins. Such variable values are available to the BEGIN block of an AWK program.
-f program-file
--file program-file
Read the AWK program source from the file program-file, instead of from the first command line argument. Multiple -f (or --file) options may be used.
-mf NNN
-mr NNN
Set various memory limits to the value NNN. The f flag sets the maximum number of fields, and the r flag sets the maximum record size. These two flags and the -m option are from an earlier version of the Bell Laboratories research version of UNIX awk. They are ignored by gawk, since gawk has no pre-defined limits. (Current versions of the Bell Laboratories awk no longer accept them.)
-O
--optimize
Enable optimizations upon the internal representation of the program. Currently, this includes just simple constant-folding. The gawk maintainer hopes to add additional optimizations over time.
-W compat
-W traditional
--compat
--traditional
Run in compatibility mode. In compatibility mode, gawk behaves identically to UNIX awk; none of the GNU -specific extensions are recognized. The use of --traditional is preferred over the other forms of this option. See GNU EXTENSIONS, below, for more information.
-W copyleft
-W copyright
--copyleft
--copyright
Print the short version of the GNU copyright information message on the standard output and exit successfully.
-W dump-variables[=file]
--dump-variables[=file]
Print a sorted list of global variables, their types and final values to file. If no file is provided, gawk uses a file named awkvars.out in the current directory.
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 large program with a lot of functions, and you want to be sure that your functions dont inadvertently use global variables that you meant to be local. (This is a particularly easy mistake to make with simple variable names like i, j, and so on.)
-W exec file
--exec file
Similar to -f, however, this is option is the last one processed. This should be used with #! scripts, particularly for CGI applications, to avoid passing in options or source code (!) on the command line from a URL. This option disables command-line variable assignments.
-W gen-po
--gen-po
Scan and parse the AWK program, and generate a GNU .po format file on standard output with entries for all localizable strings in the program. The program itself is not executed. See the GNU gettext distribution for more information on .po files.
-W help
-W usage
--help
--usage
Print a relatively short summary of the available options on the standard output. (Per the GNU Coding Standards, these options cause an immediate, successful exit.)
-W lint[=value]
--lint[=value]
Provide warnings about constructs that are dubious or non-portable to other AWK implementations. With an optional argument of fatal, lint warnings become fatal errors. This may be drastic, but its use will certainly encourage the development of cleaner AWK programs. With an optional argument of invalid, only warnings about things that are actually invalid are issued. (This is not fully implemented yet.)
-W lint-old
--lint-old
Provide warnings about constructs that are not portable to the original version of Unix awk.
-W non-decimal-data
--non-decimal-data
Recognize octal and hexadecimal values in input data. Use this option with great caution!
-W posix
--posix
This turns on compatibility mode, with the following additional restrictions:
- \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.
-W profile[=prof_file]
--profile[=prof_file]
Send profiling data to prof_file. The default is awkprof.out. When run with gawk, the profile is just a "pretty printed" version of the program. When run with pgawk, the profile contains execution counts of each statement in the program in the left margin and function call counts for each user-defined function.
-W re-interval
--re-interval
Enable the use of interval expressions in regular expression matching (see Regular Expressions, below). Interval expressions were not traditionally available in the AWK language. The POSIX standard added them, to make awk and egrep consistent with each other. However, their use is likely to break old AWK programs, so gawk only provides them if they are requested with this option, or when --posix is specified.
-W source program-text
--source program-text
Use program-text as AWK program source code. This option allows the easy intermixing of library functions (used via the -f and --file options) with source code entered on the command line. It is intended primarily for medium to large AWK programs used in shell scripts.
-W use-lc-numeric
--use-lc-numeric
This forces gawk to use the locales decimal point character when parsing input data. Although the POSIX standard requires this behavior, and gawk does so when --posix is in effect, the default is to follow traditional behavior and use a period as the decimal point, even in locales where the period is not the decimal point character. This option overrides the default behavior, without the full draconian strictness of the --posix option.
-W version
--version
Print version information for this particular copy of gawk on the standard output. This is useful mainly for knowing if the current copy of gawk on your system is up to date with respect to whatever the Free Software Foundation is distributing. This is also useful when reporting bugs. (Per the GNU Coding Standards, these options cause an immediate, successful exit.)
Print the first column from all rows:
awk '{print $1}'
Print the first and third columns from all rows:
awk '{print $1, $3}'
The comma between the column parameters in the previous command will put a space between the outputted columns. However, you can change this behavior and use your own formatting:
awk '{print $1 " --- " $3}'
By default, awk will parse a row into columns using a space as the delimiter. The delimiter can be changed with the -F command line switch.
For example, change the delimiter to a semicolon:
awk -F: '{print $2}'
The field delimiter could be anything such as an equal sign, -F=, or a period, -F..
There are plenty of situations where you might need to print the last column from a given row, but you do not know how many columns are on that given row. The built-in variable NF can be used to solve this.
awk '{print $NF}'
Another built-in variable is NR which always contains the current row number. This can be used to do such things as printing the last column from only the first row:
awk 'NR==1 {print $NF}'
If you want to print particular columns only from rows that match certain conditions, you can pass a regular expression:
awk '/regular-expression-to-match/ {print $1}'
You can also invert your regular expression match by putting an exclamation mark outside of the search field:
awk '!/regular-expression-to-match/ {print $1}'