awk [-Ffs] [-v var=val] [-V] [-C] [-c] [-a] [-e] [--] 'program' file ... awk [-Ffs] -f source-file [-f source-file ...] [-v var=val] [-V] [-C] [-c] [-a] [-e] [--] file ...
The `-v' option only has room to set one variable, but you can use it more than once, setting another variable each time, like this: `-v foo=1 -v bar=2'.
This is useful if you have file names that start with `-', or in shell scripts, if you have file names that will be specified by the user and that might start with `-'.
In compatibility mode, as a special case, if the value of fs supplied to the `-F' option is `t', then FS is set to the tab character ("\t"). Also, the `-C' and `-V' options are not recognized.
If the `-f' option is not used, then the first non-option command line argument is expected to be the program text.
The `-f' option may be used more than once on the command line. Then awk reads its program source from all of the named files, as if they had been concatenated together into one big file. This is useful for creating libraries of awk functions. Useful functions can be written once, and then retrieved from a standard place, instead of having to be included into each individual program. You can still type in a program at the terminal and use library functions, by specifying `-f /dev/tty'. awk will read a file from the terminal to use as part of the awk program. After typing your program, type Control-d (the end-of-file character) to terminate it.
All these arguments are made available to your awk program in the ARGV array (see section Built-in Variables). Command line options and the program text (if present) are omitted from the ARGV array. All other arguments, including variable assignments, are included.
The distinction between file name arguments and variable-assignment arguments is made when awk is about to open the next input file. At that point in execution, it checks the "file name" to see whether it is really a variable assignment; if so, awk sets the variable instead of reading a file.
Therefore, the variables actually receive the specified values after all previously specified files have been read. In particular, the values of variables assigned in this fashion are not available inside a BEGIN rule (see section BEGIN and END Special Patterns), since such rules are run before awk begins scanning the argument list.
In some earlier implementations of awk, when a variable assignment occurred before any file names, the assignment would happen before the BEGIN rule was executed. Some applications came to depend upon this "feature". When awk was changed to be more consistent, the `-v' option was added to accomodate applications that depended upon this old behaviour.
The variable assignment feature is most useful for assigning to variables such as RS, OFS, and ORS, which control input and output formats, before scanning the data files. It is also useful for controlling state if multiple passes are needed over a data file. For example:
awk 'pass == 1 { pass 1 stuff }
pass == 2 { pass 2 stuff }' pass=1 datafile pass=2 datafile
But in gawk, if the file name supplied in the `-f' option does not contain a `/', then gawk searches a list of directories (called the search path), one by one, looking for a file with the specified name.
The search path is actually a string containing directory names separated by colons. gawk gets its search path from the AWKPATH environment variable. If that variable does not exist, gawk uses the default path, which is `.:/usr/lib/awk:/usr/local/lib/awk'.
The search path feature is particularly useful for building up libraries of useful awk functions. The library files can be placed in a standard directory that is in the default path, and then specified on the command line with a short file name. Otherwise, the full file name would have to be typed for each file.
Path searching is not done if gawk is in compatibility mode. See section Invocation of awk.
Note: if you want files in the current directory to be found, you must include the current directory in the path, either by writing `.' as an entry in the path, or by writing a null entry in the path. (A null entry is indicated by starting or ending the path with a colon, or by placing two colons next to each other (`::').) If the current directory is not included in the path, then files cannot be found in the current directory. This path search mechanism is identical to the shell's.
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