perl special variables ..ARGV

just had a reason to use $ARGV in a perl one liner


ARGV The special filehandle that iterates over command-line file-filenames
names in @ARGV. Usually written as the null filehandle in the
angle operator "<>". Note that currently "ARGV" only has its
magical effect within the "<>" operator; elsewhere it is just a
plain filehandle corresponding to the last file opened by "<>".
In particular, passing "\*ARGV" as a parameter to a function
that expects a filehandle may not cause your function to
automatically read the contents of all the files in @ARGV.


more perl special variables can be found in the perlvar manpage

Float spanning columns in LaTeX

Use figure* and table* to produce floats which spans across both the columns in a two column article

diff/patch

copied from http://kegel.com/academy/opensource.html

Making Patches

To create a patch, you run a program called diff, and save its output to a file. For instance, if the original source tree is in directory "foobar.old", and your new sources are in directory "foobar.new", the command

diff -Naur foobar.old foobar.new > blarg.patch

will create the file 'blarg.patch' containing your changes in 'unified context diff' format.

Using Patches

To use a patch -- that is, to automatically carry out the changes described in a patch file -- you run a program called patch. For instance, if you're trying to apply the patch 'blarg.patch' to a package called foobar-0.17, you might say

cd foobar-0.17; patch -p1 < ../blarg.patch

That would merge the changes from blarg.patch into your source tree. (The -p1 tells patch to ignore the first directory in filenames in the patch; that way a patch generated against the directory foobar-0.11 will still apply properly.)

indentations

So, you can either get rid of GNU emacs, or change it to use saner
values.  To do the latter, you can stick the following in your .emacs file:

(defun linux-c-mode ()
 "C mode with adjusted defaults for use with the Linux kernel."
 (interactive)
 (c-mode)
 (c-set-style "K&R")
 (setq c-basic-offset 8))

use -kr and -i8 options with indent

(stands for "K&R, 8 character indents"). 

Spacing in Math Mode (LaTeX)

n a math environment, LaTeX ignores the spaces you type and puts in the spacing that it thinks is best. LaTeX formats mathematics the way it's done in mathematics texts. If you want different spacing, LaTeX provides the following four commands for use in math mode:

1. \; - a thick space

2. \: - a medium space

3. \, - a thin space

4. \! - a negative thin space

calculating average using perl

perl -lan -e 'BEGIN{$sum=0;$num = 0}' -e '$sum += $F[0]; $num++; END{$avg=$sum/$num;print "avg:$avg"}' data.dat

to find the average of the first column in a file

search in Emacs [ word under the cursor]

C-s C-w , appends the rest of the word under the cursor to the search pattern.

\[ or $$ instead of displaymath

You can use \[ math formula \] or $$math formula$$ instead of
\begin{displaymath}
math formula
\end{display math}

this is particularlty useful if you dont want to write small formula and don't want to break the paragraph to type it.

Redirections in Bash

command > filename 2>&1
directs both standard output and standard error to the file filename

command 2>&1 > filename
directs only the standard output to file, filename because the standard error was duplicated as standard output before the standard output was redirected

setting page ranges while printing

`lp` allows you to give the page ranges to print ,

-P page-list
Specifies which pages to print in the document. The list can contain a list of numbers and ranges (#-#) separated by commas (e.g. 1,3-5,16).

latex fullpage

\usepackage{fullpage} for efficient use of paper realestate

rectangle select in Emacs

Working with rows & columns (rectangles)

A "rectangle" is one or more columns of text in one or more rows. Commands are available to delete rectangles, fill them with spaces, or cut and paste them.

To delineate a rectangle for a command to work on, set a mark in the first row to the left of the first column (i.e., the top left of the rectangle).

Move the cursor to the last row, then to the right of the last column (i.e. the bottom right of the rectangle).

To delete the rectangle, type Esc-x delete-rectangle

To cut a rectangle, type Esc-x kill-rectangle

To paste a killed rectangle in a new location, move the cursor to wherever the rectangle is to go and type Esc-x yank-rectangle

To replace the contents of a rectangle with spaces, type Esc-x clear-rectangle

To fill the area of the rectangle with spaces and push the original rectangle right, type Esc-x open-rectangle

script command

The script command is helpful to get a transcript of the commands you enter and the output displayed on the terminal.
You start by typing script filename ( in the absence of filename the default filename is typescript)

The script command ends when you exit the forked shell by typing control-d.
more info on man script ofcourse ;)

commandline arguments in perl

unlike C , in perl the first command line argument is ARGV[0] and not ARGV[1]
$#ARGV is the subscript of the last element of the @ARGV array

latex row height in tabular

\renewcommand\arraystretch{MyValue}% (MyValue=1.0 is for standard spacing)

Common C++ error

error:ISO C++ forbids defining types within return type
error:return type specification for constructor invalid

This mainly happens when you forget to end the class declaration with a ';'

gengetopt

http://www.gnu.org/software/gengetopt/gengetopt.html
If an option is given multiple times

If an option is specified as multiple, then it can be specified multiple times at command line. In this case, say the option is called foo, the generated foo_given field in the args structure contains the number of times it was specified and the generated field foo_arg is an array containing all the values that were specified for this option.

Notice that if a default value is specified for a multiple option, that value is assigned to the option only if no other value is specified on the command line (and the corresponding _given field will be set to 1), i.e., a default value IS NOT always part of the values of a multiple option.

for (i = 0; i < args_info.string_given; ++i)

   printf ("passed string: %s\n", args_info.string_arg[i]);

C++

http://www.stanford.edu/class/cs106b/winterhandouts/H06%20C++%20streams.pdf

fs.open(filename.c_str());

The above line attempts to open the file with the given filename (searching in the current directory). Note that open member function takes in a char* argument and not a C++-style string, so you must use c_str to convert it. (Sigh, this is just a weird artifact of the stream libraries being completed before the string library). Opening the file may or may not succeed (depending on whether the named file exists, what permissions it has, etc.), so before you proceed, you should check the state of the stream.

if (fs.fail()) return;

The call to fail checks if the state of the stream is unhappy, in this case, it will determine if the file was properly opened. This is essential before we start trying to output to the stream (in the same way that we check if a FILE* is NULL in C).

Emacs

a few emacs shortcuts

M-/ autocompletion. It's based on the tokens in the currently open buffers.

ESC-u change a word into uppercase
ESC-c capitalise a word
C-x C-u upcase region

GNU Build system

The top directory should atleast have Makefile.am and configure.in

Makefile.am in the top directory should have the subdirs where Makefiles need to be created.
e.g Makefile.am for toplevel
+++++
SUBDIRS = src
+++++

and in the directory "src" you can possibly have the following Makefile.am
++++++++++++++++
bin_PROGRAMS = hello
hello_SOURCES = hello.cpp

++++++++++++++++++

Next you need to have a configure.in in your toplevel directory
following is just a template , read and understand on your own , i have no explanations
++++++++++++++++++
AC_INIT(src/hello.cpp)
AM_CONFIG_HEADER(config.h)
AM_INIT_AUTOMAKE(hello, 0.1)
AC_PROG_CXX
AC_PROG_INSTALL
AC_OUTPUT(Makefile src/Makefile)
++++++++++++++++
you are pretty much done with the files at this stage ,

$aclocal
$autoconf
$touch AUTHORS NEWS README ChangeLog
$autoheader
$automake --add-missing