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Full Discussion: UNIX basics
Top Forums UNIX for Dummies Questions & Answers UNIX basics Post 302920668 by DGPickett on Friday 10th of October 2014 05:23:54 PM
Old 10-10-2014
A Parameter is an Argument with a stuck up attitude? An Argument is a Parameter with a bad attitude? Smilie

Yes, UNIX is an O/S, the variables and such come with languages, applications, the O/S kernel and libraries. UNIX is mostly written in C, or these days maybe C++, and comes with libraries that are most accessible in those languages. Other languages wrote interfaces to them. Since libraries are in execution or object code, any language can link to them and pass and receive data, sometimes with other real world side effects like writing a file.

The shell is a slightly more human friendly, interactive- and interpretation-oriented language. There are many variations on the shell.

Variables exist in the memory space of the application's process and in the UNIX kernel. They usually conform to datatypes of the common languages and CPU hardware, like the 4 byte or 32 bit 2's complement big-endian signed binary integer, or int. All memory and file space is alike until a context is thrown over it. If it is string or character data, still the glyphs you see when it is prints and the amount of space it takes is context-dependent: ASCII, EBCDIC, UNICODE, UTF-8, EUC, Latin-1, iso8859-1, . . . . Memory can have code and variables in it, as well as unallocated spaces. For a compiler or link loader, the code is also just data out of context. Most code is CPU-specific and somewhat O/S specific (object code), but some is for an interpreter like the shell (scripts or *codes) or to instruct a compiler (source code). Source code is text from humans that is compiled into object code for execution. Some programs can be executed directly, and others are just libraries of callable subroutines and other constants to assist runnable programs and each other. The UNIX kernel is the first loaded program at the bottom of memory by bootload, which serves all the running processes, some of which are part of the UNIX O/S.

Knowing the big picture keeps the snow level down. Everything runs on top of this, one way or the other. Every O/S is many ways similar.

Last edited by DGPickett; 10-10-2014 at 06:31 PM..
 

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iconv_open(3)						     Library Functions Manual						     iconv_open(3)

NAME
iconv_open - Opens a character codeset converter LIBRARY
The iconv library (libiconv) SYNOPSIS
#include <iconv.h> iconv_t iconv_open( const char *tocode, const char *fromcode); STANDARDS
Interfaces documented on this reference page conform to industry standards as follows: iconv_open(): XSH5.0 Refer to the standards(5) reference page for more information about industry standards and associated tags. PARAMETERS
Specifies the destination codeset. Specifies the originating codeset. DESCRIPTION
The iconv_open() function initializes a codeset converter. This converter is used by the iconv function to convert characters from one codeset to another. The iconv_open() function finds the converter that performs the character conversion specified by the fromcode and tocode parameters, initializes that converter, then returns a conversion descriptor of type iconv_t that identifies the converter. The conversion descriptor returned by this function remains valid until the descriptor is closed for the process in which the application is run. The descriptor can be closed by an iconv_close() call in which the descriptor is an argument or by a call to one of the exec() functions. Note that standards do not define where codeset converters reside or how vendors implement them. [Tru64 UNIX] The iconv_open() function searches for an algorithmic converter. If it does not find an algorithmic converter for the speci- fied codesets, the function then searches for a table converter. The algorithmic and table converter file names are formed by concatenating the tocode parameter codeset name onto the fromcode parameter codeset name, with an underscore between the two, for example: fromcode=ct tocode=ISO8859-1 Converter name=ct_ISO8859-1 [Tru64 UNIX] The iconv_open() function searches for an algorithmic converter in an iconv subdirectory of the directory specified in the LOCPATH environment variable. The function searches for a table converter in an iconvTable subdirectory of the directory specified in the LOCPATH environment variable. If LOCPATH is not defined, iconv_open() uses the default value: /usr/lib/nls/loc. [Tru64 UNIX] The LOCPATH variable also overrides the default search path (/usr/lib/nls/loc) that is used to find locales. If this variable is defined, it must therefore specify a search path that application and system software can use to find both locales and converters. The LOCPATH variable is not defined by any standard, so use of the variable should be limited to testing locales or converters under development. RETURN VALUES
On successful completion, the iconv_open() function returns a conversion descriptor. Otherwise, the function returns -1 cast to iconv_t and sets errno to indicate the error. ERRORS
If any of the following conditions occur, the iconv_open() function sets errno to the corresponding value: The number of file descriptors specified by the OPEN_MAX configuration variable is currently open in the calling process. [Tru64 UNIX] Either the OPEN_MAX value or the per-process soft descriptor limit is checked. [Tru64 UNIX] The path used to find the codeset converter is longer than PATH_MAX. Too many files are currently open in the system. Insufficient virtual memory is available. The conversion specified by the fromcode and tocode parameters is not supported. [Tru64 UNIX] This condition may also indicate an incorrect LOCPATH setting because support for the specified conversion is deter- mined by finding a converter whose name also specifies that conversion. RELATED INFORMATION
Commands: genxlt(1), iconv(1) Functions: iconv(3), iconv_close(3) Others: iconv_intro(5), standards(5) delim off iconv_open(3)
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