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Full Discussion: [BASH] Getting a filename its extension
Top Forums Shell Programming and Scripting [BASH] Getting a filename its extension Post 302943259 by Scrutinizer on Wednesday 6th of May 2015 10:53:13 PM
Old 05-06-2015
Hi Sea, the previous read command is not useless, it is there to cater for the possibilty that a filename has no extension. It splits the filename into a first part before the first dot and (into variable first) and a last part (into variable last) that contains everything after the first dot.

If the file contains no extension, then the variablelast will be empty and thus echo "${last##*.}" will produce an empty string ("").
If there is an extension then echo "${last##*.}" will produce the part after the last dot..

It is indeed not REGEX; it is parameter expansion...
Last edited by Scrutinizer; 05-06-2015 at 11:58 PM..
This User Gave Thanks to Scrutinizer For This Post:
sea
 

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LEARN ABOUT LINUX

dot

DOT(P)							     POSIX Programmer's Manual							    DOT(P)

NAME

       dot - execute commands in the current environment

SYNOPSIS

       . file

DESCRIPTION

       The shell shall execute commands from the file in the current environment.

       If  file does not contain a slash, the shell shall use the search path specified by PATH to find the directory containing file. Unlike nor-
       mal command search, however, the file searched for by the dot utility need not be executable. If no readable file is found, a  non-interac-
       tive shell shall abort; an interactive shell shall write a diagnostic message to standard error, but this condition shall not be considered
       a syntax error.

OPTIONS

       None.

OPERANDS

       See the DESCRIPTION.

STDIN

       Not used.

INPUT FILES

       See the DESCRIPTION.

ENVIRONMENT VARIABLES

       See the DESCRIPTION.

ASYNCHRONOUS EVENTS

       Default.

STDOUT

       Not used.

STDERR

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES

       None.

EXTENDED DESCRIPTION

       None.

EXIT STATUS

       Returns the value of the last command executed, or a zero exit status if no command is executed.

CONSEQUENCES OF ERRORS

       Default.

       The following sections are informative.

APPLICATION USAGE

       None.

EXAMPLES

	      cat foobar
	      foo=hello bar=world. foobar
	      echo $foo $bar
	      hello world

RATIONALE

       Some older implementations searched the current directory for the file, even if the value of PATH disallowed it.  This behavior was omitted
       from  this volume of IEEE Std 1003.1-2001 due to concerns about introducing the susceptibility to trojan horses that the user might be try-
       ing to avoid by leaving dot out of PATH .

       The KornShell version of dot takes optional arguments that are set to the positional parameters. This is a valid extension  that  allows  a
       dot script to behave identically to a function.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Special Built-In Utilities

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
       Electrical  and	Electronics  Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE
       and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can  be  obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003								    DOT(P)
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