awk or gawk (gnu awk)
Find and Replace text, database sort/validate/index
Syntax
awk <options> 'Program' Input-File1 Input-File2 ...
awk -f PROGRAM-FILE <options> Input-File1 Input-File2 ...
Key
-F FS
--field-separator FS
Use FS for the input field separator (the value of the `FS'
predefined variable).
-f PROGRAM-FILE
--file PROGRAM-FILE
Read the `awk' program source from the file PROGRAM-FILE, instead
of from the first command line argument.
-mf NNN
-mr NNN
The `f' flag sets the maximum number of fields, and the `r' flag
sets the maximum record size. These options are ignored by
`gawk', since `gawk' has no predefined limits; they are only for
compatibility with the Bell Labs research version of Unix `awk'.
-v VAR=VAL
--assign VAR=VAL
Assign the variable VAR the value VAL before program execution
begins.
-W traditional
-W compat
--traditional
--compat
Use compatibility mode, in which `gawk' extensions are turned off.
-W lint
--lint
Give warnings about dubious or non-portable `awk' constructs.
-W lint-old
--lint-old
Warn about constructs that are not available in the original
Version 7 Unix version of `awk'.
-W posix
--posix
Use POSIX compatibility mode, in which `gawk' extensions are
turned off and additional restrictions apply.
-W re-interval
--re-interval
Allow interval expressions, in regexps.
-W source=PROGRAM-TEXT
--source PROGRAM-TEXT
Use PROGRAM-TEXT as `awk' program source code. This option allows
mixing command line source code with source code from files, and is
particularly useful for mixing command line programs with library
functions.
--
Signal the end of options. This is useful to allow further
arguments to the `awk' program itself to start with a `-'. This
is mainly for consistency with POSIX argument parsing conventions.
'Program'
A series of patterns and actions: see below
Input-File
If no Input-File is specified then `awk' applies the Program to
"standard input", (piped output of some other command or the terminal.
Typed input will continue until end-of-file (typing `Control-d')
Basic functions
The basic function of awk is to search files for lines (or other units of text) that contain a pattern. When a line matches, awk performs a specific action on that line.
The Program statement that tells `awk’ what to do; consists of a series of “rules”. Each rule specifies one pattern to search for, and one action to perform when that pattern is found.
For ease of reading, each line in an `awk’ program is normally a separate Program statement , like this:
pattern { action }
pattern { action }
...
e.g. Display lines from my_file containing the string “123″ or “abc” or “some text”:
awk '/123/ { print $0 }
/abc/ { print $0 }
/some text/ { print $0 }' my_file
A regular expression enclosed in slashes (`/’) is an `awk’ pattern that matches every input record whose text belongs to that set. e.g. the pattern /foo/ matches any input record containing the three characters `foo’, *anywhere* in the record.
`awk’ patterns may be one of the following:
/Regular Expression/ - Match =
Pattern && Pattern - AND
Pattern || Pattern - OR
! Pattern - NOT
Pattern ? Pattern : Pattern - If, Then, Else
Pattern1, Pattern2 - Range Start - end
BEGIN - Perform action BEFORE input file is read
END - Perform action AFTER input file is read
In addition to simple pattern matching `awk’ has a huge range of text and arithmetic Functions, Variables and Operators.
`gawk’ will ignore newlines after any of the following:
, { ? : || && do else
Comments – start with a `#’, and continue to the end of the line:
# This program prints a nice friendly message
Examples
This program prints the length of the longest input line:
awk '{ if (length($0) > max) max = length($0) }
END { print max }' data
This program prints every line that has at least one field. This is an easy way to delete blank lines from a file (or rather, to
create a new file similar to the old file but from which the blank lines have been deleted)
awk 'NF > 0' data
This program prints seven random numbers from zero to 100, inclusive.
awk 'BEGIN { for (i = 1; i <= 7; i++)
print int(101 * rand()) }'
This program prints the total number of bytes used by FILES.
ls -lg FILES | awk '{ x += $5 } ; END { print "total bytes: " x }'
This program prints a sorted list of the login names of all users.
awk -F: '{ print $1 }' /etc/passwd | sort
This program counts lines in a file.
awk 'END { print NR }' data
This program prints the even numbered lines in the data file. If you were to use the expression `NR % 2 == 1′ instead, it would print the odd numbered lines.
awk 'NR % 2 == 0' data
As many of you iPhone consumers may know, Flash isn’t supported and will probably never be supported. The new up and coming iPad (Apple Tablet) will be running a version of the iPhone operating system and will probably have the same exact restrictions. The reason Apple doesn’t want to support Flash is because it allows third party developers to create applications for the iPhone (and soon iPad) for free. Everyone would be making little Flash-lets for the Apple devices and Apple would lose income (that’s dollars) from their app store. Read more…
STChat is a simple telnet chat server that runs on Linux, Windows and MAC. I’ve only tested this on Linux so i can’t speak for the other OS’s. The chat system is really simple, supports colors, multiple terminal types (vt100 etc), usernames and admin mode. Putty, Linux telnet, and Windows telnet seem to work just fine when connecting to the chat server. No special installation is needed except that you do need a Java Runtime Environment (JRE) to run the server. Simply unpack the package and run ‘java stc 2020` to start the server on port 2020. If you want to run STchat on the standard telnet port, port 23, you’ll need to run the server as root. e.g. java stc 23