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Language Summary

An awk program consists of a sequence of zero or more pattern-action statements and optional function definitions. One or the other of the pattern and action may be omitted.

pattern    { action statements }
          { action statements }

function name(parameter list)     { action statements }

gawk first reads the program source from the program-file(s), if specified, or from the first non-option argument on the command line. The `-f' option may be used multiple times on the command line. gawk reads the program text from all the program-file files, effectively concatenating them in the order they are specified. This is useful for building libraries of awk functions, without having to include them in each new awk program that uses them. To use a library function in a file from a program typed in on the command line, specify `--source 'program'', and type your program in between the single quotes. See section Command Line Options.

The environment variable AWKPATH specifies a search path to use when finding source files named with the `-f' option. The default path, which is `.:/usr/local/share/awk'(27) is used if AWKPATH is not set. If a file name given to the `-f' option contains a `/' character, no path search is performed. See section The AWKPATH Environment Variable.

gawk compiles the program into an internal form, and then proceeds to read each file named in the ARGV array. The initial values of ARGV come from the command line arguments. If there are no files named on the command line, gawk reads the standard input.

If a "file" named on the command line has the form `var=val', it is treated as a variable assignment: the variable var is assigned the value val. If any of the files have a value that is the null string, that element in the list is skipped.

For each record in the input, gawk tests to see if it matches any pattern in the awk program. For each pattern that the record matches, the associated action is executed.

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