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diff --git a/gawk.info-1 b/gawk.info-1 deleted file mode 100644 index e6f2e750..00000000 --- a/gawk.info-1 +++ /dev/null @@ -1,1069 +0,0 @@ -This is Info file gawk.info, produced by Makeinfo-1.54 from the input -file gawk.texi. - - This file documents `awk', a program that you can use to select -particular records in a file and perform operations upon them. - - This is Edition 0.15 of `The GAWK Manual', -for the 2.15 version of the GNU implementation -of AWK. - - Copyright (C) 1989, 1991, 1992, 1993 Free Software Foundation, Inc. - - Permission is granted to make and distribute verbatim copies of this -manual provided the copyright notice and this permission notice are -preserved on all copies. - - Permission is granted to copy and distribute modified versions of -this manual under the conditions for verbatim copying, provided that -the entire resulting derived work is distributed under the terms of a -permission notice identical to this one. - - Permission is granted to copy and distribute translations of this -manual 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. - - -File: gawk.info, Node: Top, Next: Preface, Prev: (dir), Up: (dir) - -General Introduction -******************** - - This file documents `awk', a program that you can use to select -particular records in a file and perform operations upon them. - - This is Edition 0.15 of `The GAWK Manual', -for the 2.15 version of the GNU implementation -of AWK. - -* Menu: - -* Preface:: What you can do with `awk'; brief history - and acknowledgements. -* Copying:: Your right to copy and distribute `gawk'. -* This Manual:: Using this manual. - Includes sample input files that you can use. -* Getting Started:: A basic introduction to using `awk'. - How to run an `awk' program. - Command line syntax. -* Reading Files:: How to read files and manipulate fields. -* Printing:: How to print using `awk'. Describes the - `print' and `printf' statements. - Also describes redirection of output. -* One-liners:: Short, sample `awk' programs. -* Patterns:: The various types of patterns - explained in detail. -* Actions:: The various types of actions are - introduced here. Describes - expressions and the various operators in - detail. Also describes comparison expressions. -* Expressions:: Expressions are the basic building - blocks of statements. -* Statements:: The various control statements are - described in detail. -* Arrays:: The description and use of arrays. - Also includes array-oriented control - statements. -* Built-in:: The built-in functions are summarized here. -* User-defined:: User-defined functions are described in detail. -* Built-in Variables:: Built-in Variables -* Command Line:: How to run `gawk'. -* Language History:: The evolution of the `awk' language. -* Installation:: Installing `gawk' under - various operating systems. -* Gawk Summary:: `gawk' Options and Language Summary. -* Sample Program:: A sample `awk' program with a - complete explanation. -* Bugs:: Reporting Problems and Bugs. -* Notes:: Something about the - implementation of `gawk'. -* Glossary:: An explanation of some unfamiliar terms. -* Index:: - - -File: gawk.info, Node: Preface, Next: Copying, Prev: Top, Up: Top - -Preface -******* - - If you are like many computer users, you would frequently like to -make changes in various text files wherever certain patterns appear, or -extract data from parts of certain lines while discarding the rest. To -write a program to do this in a language such as C or Pascal is a -time-consuming inconvenience that may take many lines of code. The job -may be easier with `awk'. - - The `awk' utility interprets a special-purpose programming language -that makes it possible to handle simple data-reformatting jobs easily -with just a few lines of code. - - The GNU implementation of `awk' is called `gawk'; it is fully upward -compatible with the System V Release 4 version of `awk'. `gawk' is -also upward compatible with the POSIX (draft) specification of the -`awk' language. This means that all properly written `awk' programs -should work with `gawk'. Thus, we usually don't distinguish between -`gawk' and other `awk' implementations in this manual. - - This manual teaches you what `awk' does and how you can use `awk' -effectively. You should already be familiar with basic system commands -such as `ls'. Using `awk' you can: - - * manage small, personal databases - - * generate reports - - * validate data - - * produce indexes, and perform other document preparation tasks - - * even experiment with algorithms that can be adapted later to other - computer languages - -* Menu: - -* History:: The history of `gawk' and - `awk'. Acknowledgements. - - -File: gawk.info, Node: History, Prev: Preface, Up: Preface - -History of `awk' and `gawk' -=========================== - - The name `awk' comes from the initials of its designers: Alfred V. -Aho, Peter J. Weinberger, and Brian W. Kernighan. The original version -of `awk' was written in 1977. In 1985 a new version made the -programming language more powerful, introducing user-defined functions, -multiple input streams, and computed regular expressions. This new -version became generally available with System V Release 3.1. The -version in System V Release 4 added some new features and also cleaned -up the behavior in some of the "dark corners" of the language. The -specification for `awk' in the POSIX Command Language and Utilities -standard further clarified the language based on feedback from both the -`gawk' designers, and the original `awk' designers. - - The GNU implementation, `gawk', was written in 1986 by Paul Rubin -and Jay Fenlason, with advice from Richard Stallman. John Woods -contributed parts of the code as well. In 1988 and 1989, David -Trueman, with help from Arnold Robbins, thoroughly reworked `gawk' for -compatibility with the newer `awk'. Current development (1992) focuses -on bug fixes, performance improvements, and standards compliance. - - We need to thank many people for their assistance in producing this -manual. Jay Fenlason contributed many ideas and sample programs. -Richard Mlynarik and Robert J. Chassell gave helpful comments on early -drafts of this manual. The paper `A Supplemental Document for `awk'' -by John W. Pierce of the Chemistry Department at UC San Diego, -pinpointed several issues relevant both to `awk' implementation and to -this manual, that would otherwise have escaped us. David Trueman, Pat -Rankin, and Michal Jaegermann also contributed sections of the manual. - - The following people provided many helpful comments on this edition -of the manual: Rick Adams, Michael Brennan, Rich Burridge, Diane Close, -Christopher ("Topher") Eliot, Michael Lijewski, Pat Rankin, Miriam -Robbins, and Michal Jaegermann. Robert J. Chassell provided much -valuable advice on the use of Texinfo. - - Finally, we would like to thank Brian Kernighan of Bell Labs for -invaluable assistance during the testing and debugging of `gawk', and -for help in clarifying numerous points about the language. - - -File: gawk.info, Node: Copying, Next: This Manual, Prev: Preface, Up: Top - -GNU GENERAL PUBLIC LICENSE -************************** - - Version 2, June 1991 - - Copyright (C) 1989, 1991 Free Software Foundation, Inc. - 675 Mass Ave, Cambridge, MA 02139, USA - - Everyone is permitted to copy and distribute verbatim copies - of this license document, but changing it is not allowed. - -Preamble -======== - - The licenses for most software are designed to take away your -freedom to share and change it. By contrast, the GNU General Public -License is intended to guarantee your freedom to share and change free -software--to make sure the software is free for all its users. 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Our General Public Licenses are designed to make sure that you -have the freedom to distribute copies of free software (and charge for -this service if you wish), that you receive source code or can get it -if you want it, that you can change the software or use pieces of it in -new free programs; and that you know you can do these things. - - To protect your rights, we need to make restrictions that forbid -anyone to deny you these rights or to ask you to surrender the rights. -These restrictions translate to certain responsibilities for you if you -distribute copies of the software, or if you modify it. - - For example, if you distribute copies of such a program, whether -gratis or for a fee, you must give the recipients all the rights that -you have. You must make sure that they, too, receive or can get the -source code. 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It is safest -to attach them to the start of each source file to most effectively -convey the exclusion of warranty; and each file should have at least -the "copyright" line and a pointer to where the full notice is found. - - ONE LINE TO GIVE THE PROGRAM'S NAME AND A BRIEF IDEA OF WHAT IT DOES. - Copyright (C) 19YY NAME OF AUTHOR - - This program is free software; you can redistribute it and/or modify - it under the terms of the GNU General Public License as published by - the Free Software Foundation; either version 2 of the License, or - (at your option) any later version. - - This program is distributed in the hope that it will be useful, - but WITHOUT ANY WARRANTY; without even the implied warranty of - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - GNU General Public License for more details. - - You should have received a copy of the GNU General Public License - along with this program; if not, write to the Free Software - Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. - - Also add information on how to contact you by electronic and paper -mail. - - If the program is interactive, make it output a short notice like -this when it starts in an interactive mode: - - Gnomovision version 69, Copyright (C) 19YY NAME OF AUTHOR - Gnomovision comes with ABSOLUTELY NO WARRANTY; for details - type `show w'. - This is free software, and you are welcome to redistribute it - under certain conditions; type `show c' for details. - - The hypothetical commands `show w' and `show c' should show the -appropriate parts of the General Public License. Of course, the -commands you use may be called something other than `show w' and `show -c'; they could even be mouse-clicks or menu items--whatever suits your -program. - - You should also get your employer (if you work as a programmer) or -your school, if any, to sign a "copyright disclaimer" for the program, -if necessary. Here is a sample; alter the names: - - Yoyodyne, Inc., hereby disclaims all copyright interest in the program - `Gnomovision' (which makes passes at compilers) written by James Hacker. - - SIGNATURE OF TY COON, 1 April 1989 - Ty Coon, President of Vice - - This General Public License does not permit incorporating your -program into proprietary programs. If your program is a subroutine -library, you may consider it more useful to permit linking proprietary -applications with the library. If this is what you want to do, use the -GNU Library General Public License instead of this License. - - -File: gawk.info, Node: This Manual, Next: Getting Started, Prev: Copying, Up: Top - -Using this Manual -***************** - - The term `awk' refers to a particular program, and to the language -you use to tell this program what to do. When we need to be careful, -we call the program "the `awk' utility" and the language "the `awk' -language." The term `gawk' refers to a version of `awk' developed as -part the GNU project. The purpose of this manual is to explain both the -`awk' language and how to run the `awk' utility. - - While concentrating on the features of `gawk', the manual will also -attempt to describe important differences between `gawk' and other -`awk' implementations. In particular, any features that are not in the -POSIX standard for `awk' will be noted. - - The term "`awk' program" refers to a program written by you in the -`awk' programming language. - - *Note Getting Started with `awk': Getting Started, for the bare -essentials you need to know to start using `awk'. - - Some useful "one-liners" are included to give you a feel for the -`awk' language (*note Useful "One-liners": One-liners.). - - A sample `awk' program has been provided for you (*note Sample -Program::.). - - If you find terms that you aren't familiar with, try looking them up -in the glossary (*note Glossary::.). - - The entire `awk' language is summarized for quick reference in *Note -`gawk' Summary: Gawk Summary. Look there if you just need to refresh -your memory about a particular feature. - - Most of the time complete `awk' programs are used as examples, but in -some of the more advanced sections, only the part of the `awk' program -that illustrates the concept being described is shown. - -* Menu: - -* Sample Data Files:: Sample data files for use in the `awk' - programs illustrated in this manual. - - -File: gawk.info, Node: Sample Data Files, Prev: This Manual, Up: This Manual - -Data Files for the Examples -=========================== - - Many of the examples in this manual take their input from two sample -data files. The first, called `BBS-list', represents a list of -computer bulletin board systems together with information about those -systems. The second data file, called `inventory-shipped', contains -information about shipments on a monthly basis. Each line of these -files is one "record". - - In the file `BBS-list', each record contains the name of a computer -bulletin board, its phone number, the board's baud rate, and a code for -the number of hours it is operational. An `A' in the last column means -the board operates 24 hours a day. A `B' in the last column means the -board operates evening and weekend hours, only. A `C' means the board -operates only on weekends. - - aardvark 555-5553 1200/300 B - alpo-net 555-3412 2400/1200/300 A - barfly 555-7685 1200/300 A - bites 555-1675 2400/1200/300 A - camelot 555-0542 300 C - core 555-2912 1200/300 C - fooey 555-1234 2400/1200/300 B - foot 555-6699 1200/300 B - macfoo 555-6480 1200/300 A - sdace 555-3430 2400/1200/300 A - sabafoo 555-2127 1200/300 C - - The second data file, called `inventory-shipped', represents -information about shipments during the year. Each record contains the -month of the year, the number of green crates shipped, the number of -red boxes shipped, the number of orange bags shipped, and the number of -blue packages shipped, respectively. There are 16 entries, covering -the 12 months of one year and 4 months of the next year. - - Jan 13 25 15 115 - Feb 15 32 24 226 - Mar 15 24 34 228 - Apr 31 52 63 420 - May 16 34 29 208 - Jun 31 42 75 492 - Jul 24 34 67 436 - Aug 15 34 47 316 - Sep 13 55 37 277 - Oct 29 54 68 525 - Nov 20 87 82 577 - Dec 17 35 61 401 - - Jan 21 36 64 620 - Feb 26 58 80 652 - Mar 24 75 70 495 - Apr 21 70 74 514 - - If you are reading this in GNU Emacs using Info, you can copy the -regions of text showing these sample files into your own test files. -This way you can try out the examples shown in the remainder of this -document. You do this by using the command `M-x write-region' to copy -text from the Info file into a file for use with `awk' (*Note Misc File -Ops: (emacs)Misc File Ops, for more information). Using this -information, create your own `BBS-list' and `inventory-shipped' files, -and practice what you learn in this manual. - - -File: gawk.info, Node: Getting Started, Next: Reading Files, Prev: This Manual, Up: Top - -Getting Started with `awk' -************************** - - The basic function of `awk' is to search files for lines (or other -units of text) that contain certain patterns. When a line matches one -of the patterns, `awk' performs specified actions on that line. `awk' -keeps processing input lines in this way until the end of the input -file is reached. - - When you run `awk', you specify an `awk' "program" which tells `awk' -what to do. The program consists of a series of "rules". (It may also -contain "function definitions", but that is an advanced feature, so we -will ignore it for now. *Note User-defined Functions: User-defined.) -Each rule specifies one pattern to search for, and one action to -perform when that pattern is found. - - Syntactically, a rule consists of a pattern followed by an action. -The action is enclosed in curly braces to separate it from the pattern. -Rules are usually separated by newlines. Therefore, an `awk' program -looks like this: - - PATTERN { ACTION } - PATTERN { ACTION } - ... - -* Menu: - -* Very Simple:: A very simple example. -* Two Rules:: A less simple one-line example with two rules. -* More Complex:: A more complex example. -* Running gawk:: How to run `gawk' programs; - includes command line syntax. -* Comments:: Adding documentation to `gawk' programs. -* Statements/Lines:: Subdividing or combining statements into lines. -* When:: When to use `gawk' and - when to use other things. - - -File: gawk.info, Node: Very Simple, Next: Two Rules, Prev: Getting Started, Up: Getting Started - -A Very Simple Example -===================== - - The following command runs a simple `awk' program that searches the -input file `BBS-list' for the string of characters: `foo'. (A string -of characters is usually called, a "string". The term "string" is -perhaps based on similar usage in English, such as "a string of -pearls," or, "a string of cars in a train.") - - awk '/foo/ { print $0 }' BBS-list - -When lines containing `foo' are found, they are printed, because -`print $0' means print the current line. (Just `print' by itself means -the same thing, so we could have written that instead.) - - You will notice that slashes, `/', surround the string `foo' in the -actual `awk' program. The slashes indicate that `foo' is a pattern to -search for. This type of pattern is called a "regular expression", and -is covered in more detail later (*note Regular Expressions as Patterns: -Regexp.). There are single-quotes around the `awk' program so that the -shell won't interpret any of it as special shell characters. - - Here is what this program prints: - - fooey 555-1234 2400/1200/300 B - foot 555-6699 1200/300 B - macfoo 555-6480 1200/300 A - sabafoo 555-2127 1200/300 C - - In an `awk' rule, either the pattern or the action can be omitted, -but not both. If the pattern is omitted, then the action is performed -for *every* input line. If the action is omitted, the default action -is to print all lines that match the pattern. - - Thus, we could leave out the action (the `print' statement and the -curly braces) in the above example, and the result would be the same: -all lines matching the pattern `foo' would be printed. By comparison, -omitting the `print' statement but retaining the curly braces makes an -empty action that does nothing; then no lines would be printed. - - -File: gawk.info, Node: Two Rules, Next: More Complex, Prev: Very Simple, Up: Getting Started - -An Example with Two Rules -========================= - - The `awk' utility reads the input files one line at a time. For -each line, `awk' tries the patterns of each of the rules. If several -patterns match then several actions are run, in the order in which they -appear in the `awk' program. If no patterns match, then no actions are -run. - - After processing all the rules (perhaps none) that match the line, -`awk' reads the next line (however, *note The `next' Statement: Next -Statement.). This continues until the end of the file is reached. - - For example, the `awk' program: - - /12/ { print $0 } - /21/ { print $0 } - -contains two rules. The first rule has the string `12' as the pattern -and `print $0' as the action. The second rule has the string `21' as -the pattern and also has `print $0' as the action. Each rule's action -is enclosed in its own pair of braces. - - This `awk' program prints every line that contains the string `12' -*or* the string `21'. If a line contains both strings, it is printed -twice, once by each rule. - - If we run this program on our two sample data files, `BBS-list' and -`inventory-shipped', as shown here: - - awk '/12/ { print $0 } - /21/ { print $0 }' BBS-list inventory-shipped - -we get the following output: - - aardvark 555-5553 1200/300 B - alpo-net 555-3412 2400/1200/300 A - barfly 555-7685 1200/300 A - bites 555-1675 2400/1200/300 A - core 555-2912 1200/300 C - fooey 555-1234 2400/1200/300 B - foot 555-6699 1200/300 B - macfoo 555-6480 1200/300 A - sdace 555-3430 2400/1200/300 A - sabafoo 555-2127 1200/300 C - sabafoo 555-2127 1200/300 C - Jan 21 36 64 620 - Apr 21 70 74 514 - -Note how the line in `BBS-list' beginning with `sabafoo' was printed -twice, once for each rule. - - -File: gawk.info, Node: More Complex, Next: Running gawk, Prev: Two Rules, Up: Getting Started - -A More Complex Example -====================== - - Here is an example to give you an idea of what typical `awk' -programs do. This example shows how `awk' can be used to summarize, -select, and rearrange the output of another utility. It uses features -that haven't been covered yet, so don't worry if you don't understand -all the details. - - ls -l | awk '$5 == "Nov" { sum += $4 } - END { print sum }' - - This command prints the total number of bytes in all the files in the -current directory that were last modified in November (of any year). -(In the C shell you would need to type a semicolon and then a backslash -at the end of the first line; in a POSIX-compliant shell, such as the -Bourne shell or the Bourne-Again shell, you can type the example as -shown.) - - The `ls -l' part of this example is a command that gives you a -listing of the files in a directory, including file size and date. Its -output looks like this: - - -rw-r--r-- 1 close 1933 Nov 7 13:05 Makefile - -rw-r--r-- 1 close 10809 Nov 7 13:03 gawk.h - -rw-r--r-- 1 close 983 Apr 13 12:14 gawk.tab.h - -rw-r--r-- 1 close 31869 Jun 15 12:20 gawk.y - -rw-r--r-- 1 close 22414 Nov 7 13:03 gawk1.c - -rw-r--r-- 1 close 37455 Nov 7 13:03 gawk2.c - -rw-r--r-- 1 close 27511 Dec 9 13:07 gawk3.c - -rw-r--r-- 1 close 7989 Nov 7 13:03 gawk4.c - -The first field contains read-write permissions, the second field -contains the number of links to the file, and the third field -identifies the owner of the file. The fourth field contains the size -of the file in bytes. The fifth, sixth, and seventh fields contain the -month, day, and time, respectively, that the file was last modified. -Finally, the eighth field contains the name of the file. - - The `$5 == "Nov"' in our `awk' program is an expression that tests -whether the fifth field of the output from `ls -l' matches the string -`Nov'. Each time a line has the string `Nov' in its fifth field, the -action `{ sum += $4 }' is performed. This adds the fourth field (the -file size) to the variable `sum'. As a result, when `awk' has finished -reading all the input lines, `sum' is the sum of the sizes of files -whose lines matched the pattern. (This works because `awk' variables -are automatically initialized to zero.) - - After the last line of output from `ls' has been processed, the -`END' rule is executed, and the value of `sum' is printed. In this -example, the value of `sum' would be 80600. - - These more advanced `awk' techniques are covered in later sections -(*note Overview of Actions: Actions.). Before you can move on to more -advanced `awk' programming, you have to know how `awk' interprets your -input and displays your output. By manipulating fields and using -`print' statements, you can produce some very useful and spectacular -looking reports. - - -File: gawk.info, Node: Running gawk, Next: Comments, Prev: More Complex, Up: Getting Started - -How to Run `awk' Programs -========================= - - There are several ways to run an `awk' program. If the program is -short, it is easiest to include it in the command that runs `awk', like -this: - - awk 'PROGRAM' INPUT-FILE1 INPUT-FILE2 ... - -where PROGRAM consists of a series of patterns and actions, as -described earlier. - - When the program is long, it is usually more convenient to put it in -a file and run it with a command like this: - - awk -f PROGRAM-FILE INPUT-FILE1 INPUT-FILE2 ... - -* Menu: - -* One-shot:: Running a short throw-away `awk' program. -* Read Terminal:: Using no input files (input from - terminal instead). -* Long:: Putting permanent `awk' programs in files. -* Executable Scripts:: Making self-contained `awk' programs. - - -File: gawk.info, Node: One-shot, Next: Read Terminal, Prev: Running gawk, Up: Running gawk - -One-shot Throw-away `awk' Programs ----------------------------------- - - Once you are familiar with `awk', you will often type simple -programs at the moment you want to use them. Then you can write the -program as the first argument of the `awk' command, like this: - - awk 'PROGRAM' INPUT-FILE1 INPUT-FILE2 ... - -where PROGRAM consists of a series of PATTERNS and ACTIONS, as -described earlier. - - This command format instructs the shell to start `awk' and use the -PROGRAM to process records in the input file(s). There are single -quotes around PROGRAM so that the shell doesn't interpret any `awk' -characters as special shell characters. They also cause the shell to -treat all of PROGRAM as a single argument for `awk' and allow PROGRAM -to be more than one line long. - - This format is also useful for running short or medium-sized `awk' -programs from shell scripts, because it avoids the need for a separate -file for the `awk' program. A self-contained shell script is more -reliable since there are no other files to misplace. - - -File: gawk.info, Node: Read Terminal, Next: Long, Prev: One-shot, Up: Running gawk - -Running `awk' without Input Files ---------------------------------- - - You can also run `awk' without any input files. If you type the -command line: - - awk 'PROGRAM' - -then `awk' applies the PROGRAM to the "standard input", which usually -means whatever you type on the terminal. This continues until you -indicate end-of-file by typing `Control-d'. - - For example, if you execute this command: - - awk '/th/' - -whatever you type next is taken as data for that `awk' program. If you -go on to type the following data: - - Kathy - Ben - Tom - Beth - Seth - Karen - Thomas - `Control-d' - -then `awk' prints this output: - - Kathy - Beth - Seth - -as matching the pattern `th'. Notice that it did not recognize -`Thomas' as matching the pattern. The `awk' language is "case -sensitive", and matches patterns exactly. (However, you can override -this with the variable `IGNORECASE'. *Note Case-sensitivity in -Matching: Case-sensitivity.) - - -File: gawk.info, Node: Long, Next: Executable Scripts, Prev: Read Terminal, Up: Running gawk - -Running Long Programs ---------------------- - - Sometimes your `awk' programs can be very long. In this case it is -more convenient to put the program into a separate file. To tell `awk' -to use that file for its program, you type: - - awk -f SOURCE-FILE INPUT-FILE1 INPUT-FILE2 ... - - The `-f' instructs the `awk' utility to get the `awk' program from -the file SOURCE-FILE. Any file name can be used for SOURCE-FILE. For -example, you could put the program: - - /th/ - -into the file `th-prog'. Then this command: - - awk -f th-prog - -does the same thing as this one: - - awk '/th/' - -which was explained earlier (*note Running `awk' without Input Files: -Read Terminal.). Note that you don't usually need single quotes around -the file name that you specify with `-f', because most file names don't -contain any of the shell's special characters. Notice that in -`th-prog', the `awk' program did not have single quotes around it. The -quotes are only needed for programs that are provided on the `awk' -command line. - - If you want to identify your `awk' program files clearly as such, -you can add the extension `.awk' to the file name. This doesn't affect -the execution of the `awk' program, but it does make "housekeeping" -easier. - - -File: gawk.info, Node: Executable Scripts, Prev: Long, Up: Running gawk - -Executable `awk' Programs -------------------------- - - Once you have learned `awk', you may want to write self-contained -`awk' scripts, using the `#!' script mechanism. You can do this on -many Unix systems (1) (and someday on GNU). - - For example, you could create a text file named `hello', containing -the following (where `BEGIN' is a feature we have not yet discussed): - - #! /bin/awk -f - - # a sample awk program - BEGIN { print "hello, world" } - -After making this file executable (with the `chmod' command), you can -simply type: - - hello - -at the shell, and the system will arrange to run `awk' (2) as if you -had typed: - - awk -f hello - -Self-contained `awk' scripts are useful when you want to write a -program which users can invoke without knowing that the program is -written in `awk'. - - If your system does not support the `#!' mechanism, you can get a -similar effect using a regular shell script. It would look something -like this: - - : The colon makes sure this script is executed by the Bourne shell. - awk 'PROGRAM' "$@" - - Using this technique, it is *vital* to enclose the PROGRAM in single -quotes to protect it from interpretation by the shell. If you omit the -quotes, only a shell wizard can predict the results. - - The `"$@"' causes the shell to forward all the command line -arguments to the `awk' program, without interpretation. The first -line, which starts with a colon, is used so that this shell script will -work even if invoked by a user who uses the C shell. - - ---------- Footnotes ---------- - - (1) The `#!' mechanism works on Unix systems derived from Berkeley -Unix, System V Release 4, and some System V Release 3 systems. - - (2) The line beginning with `#!' lists the full pathname of an -interpreter to be run, and an optional initial command line argument to -pass to that interpreter. The operating system then runs the -interpreter with the given argument and the full argument list of the -executed program. The first argument in the list is the full pathname -of the `awk' program. The rest of the argument list will either be -options to `awk', or data files, or both. - - -File: gawk.info, Node: Comments, Next: Statements/Lines, Prev: Running gawk, Up: Getting Started - -Comments in `awk' Programs -========================== - - A "comment" is some text that is included in a program for the sake -of human readers, and that is not really part of the program. Comments -can explain what the program does, and how it works. Nearly all -programming languages have provisions for comments, because programs are -typically hard to understand without their extra help. - - In the `awk' language, a comment starts with the sharp sign -character, `#', and continues to the end of the line. The `awk' -language ignores the rest of a line following a sharp sign. For -example, we could have put the following into `th-prog': - - # This program finds records containing the pattern `th'. This is how - # you continue comments on additional lines. - /th/ - - You can put comment lines into keyboard-composed throw-away `awk' -programs also, but this usually isn't very useful; the purpose of a -comment is to help you or another person understand the program at a -later time. - |