In 1979, the Museum of Science and Industry in Chicago opened its "Newspaper" exhibit which used interactive LaserDiscs to allow visitors to search the front page of any Chicago Tribune newspaper. This was a very early example of public access to electronically stored information in a museum.[citation needed]
BBC English Plus Interactive (30 CDs)l
Sound could be stored in either analog or digital format and in a variety of surround sound formats; NTSC discs could carry a stereo analog audio track, plus a stereo CD-quality uncompressed PCM digital audio track, which were (EFM, CIRC, 16-bit and 44.1 kHz sample rate).[21] PAL discs could carry one pair of audio tracks, either analog or digital and the digital tracks on a PAL disc were 16-bit 44.1 kHz as on a CD; in the UK, the term "LaserVision" is used to refer to discs with analog sound, while "LaserDisc" is used for those with digital audio. The digital sound signal in both formats are EFM-encoded as in CD.[21]
Under contract from the U.S. military, Matrox produced a combination computer/LaserDisc player for instructional purposes. The computer was a 286, the LaserDisc player only capable of reading the analog audio tracks. Together they weighed 43 lb (20 kg) and sturdy handles were provided in case two people were required to lift the unit. The computer controlled the player via a 25-pin serial port at the back of the player and a ribbon cable connected to a proprietary port on the motherboard. Many of these were sold as surplus by the military during the 1990s, often without the controller software. Nevertheless, it is possible to control the unit by removing the ribbon cable and connecting a serial cable directly from the computer's serial port to the port on the LaserDisc player.
The format's instant-access capability made it possible for a new breed of LaserDisc-based video arcade games and several companies saw potential in using LaserDiscs for video games in the 1980s and 1990s, beginning in 1983 with Sega's Astron Belt. Cinematronics and American Laser Games produced elaborate arcade games that used the random-access features to create interactive movies such as Dragon's Lair and Space Ace. Similarly, the Pioneer Laseractive and Halcyon were introduced as home video game consoles that used LaserDisc media for their software.
The only cosmetic difference between an RLV disc and a regular factory-pressed LaserDiscs is their reflective Red (showing up in photos as a purple-violet or blue with some RLV discs) color resulting from the dye embedded in the reflective layer of the disc to make it recordable, as opposed to the silver mirror appearance of regular LDs. The reddish color of RLVs is very similar to DVD-R and DVD+R discs. RLVs were popular for making short-run quantities of LaserDiscs for specialized applications such as interactive kiosks and flight simulators. Another, 'single sided' form of RLV exists with the silver side being covered in small bumps. Blank RLV discs show a standard Test Card when played in a Laserdisc player.
CD-V was a hybrid format launched in the late 1980s, and carried up to five minutes of analog LaserDisc-type video content with a digital soundtrack (usually a music video), plus up to 20 minutes of digital audio CD tracks. The original 1989 release of David Bowie's retrospective Sound + Vision CD box set prominently featured a CD-V video of "Ashes to Ashes", and standalone promo CD-Vs featured the video, plus three audio tracks: "John, I'm Only Dancing", "Changes", and "The Supermen".
Bash is largely compatible with sh and incorporates usefulfeatures from the Korn shell ksh and the C shell csh.It is intended to be a conformant implementation of the IEEEPOSIX Shell and Tools portion of the IEEE POSIXspecification (IEEE Standard 1003.1).It offers functional improvements over sh for both interactive andprogramming use.
Shells offer features geared specifically forinteractive use rather than to augment the programming language. These interactive features include job control, command lineediting, command history and aliases. Each of these features isdescribed in this manual.
If parameteris null or unset, the expansion of word (or a messageto that effect if wordis not present) is written to the standard error and the shell, if itis not interactive, exits. Otherwise, the value of parameter issubstituted.
The shell exits by default upon receipt of a SIGHUP.Before exiting, an interactive shell resends the SIGHUP toall jobs, running or stopped.Stopped jobs are sent SIGCONT to ensure that they receivethe SIGHUP.To prevent the shell from sending the SIGHUP signal to aparticular job, it should be removedfrom the jobs table with the disownbuiltin (see Job Control Builtins) or markedto not receive SIGHUP using disown -h.
A shell script is a text file containing shell commands. When sucha file is used as the first non-option argument when invoking Bash,and neither the -c nor -s option is supplied(see Invoking Bash), Bash reads and executes commands from the file, then exits. Thismode of operation creates a non-interactive shell. The shell firstsearches for the file in the current directory, and looks in thedirectories in $PATH if not found there.
If commandis supplied, it replaces the shell without creating a new process.If the -l option is supplied, the shell places a dash at thebeginning of the zeroth argument passed to command.This is what the login program does.The -c option causes command to be executed with an emptyenvironment.If -a is supplied, the shell passes name as the zerothargument to command.If commandcannot be executed for some reason, a non-interactive shell exits,unless the execfail shell optionis enabled. In that case, it returns failure.An interactive shell returns failure if the file cannot be executed.A subshell exits unconditionally if exec fails.If no command is specified, redirections may be used to affectthe current shell environment. If there are no redirection errors, thereturn status is zero; otherwise the return status is non-zero.
Arguments to non-string format specifiers are treated as C language constants,except that a leading plus or minus sign is allowed, and if the leadingcharacter is a single or double quote, the value is the ASCII value ofthe following character.
If set, minor errors in the spelling of a directory component in acd command will be corrected.The errors checked for are transposed characters,a missing character, and a character too many.If a correction is found, the corrected path is printed,and the command proceeds.This option is only used by interactive shells.
If set, Bash lists the status of any stopped and running jobs beforeexiting an interactive shell. If any jobs are running, this causesthe exit to be deferred until a second exit is attempted without anintervening command (see Job Control).The shell always postpones exiting if any jobs are stopped.
Used by the select command to determine the terminal widthwhen printing selection lists.Automatically set if the checkwinsize option is enabled(see The Shopt Builtin), or in an interactive shell upon receipt of aSIGWINCH.
Controls the action of the shell on receipt of an EOF characteras the sole input. If set, the value denotes the numberof consecutive EOF characters that can be read as thefirst character on an input linebefore the shell will exit. If the variable exists but does nothave a numeric value, or has no value, then the default is 10.If the variable does not exist, then EOF signifies the end of input to the shell. This is only in effect for interactive shells.
Used by the select command to determine the column lengthfor printing selection lists.Automatically set if the checkwinsize option is enabled(see The Shopt Builtin), or in an interactive shell upon receipt of aSIGWINCH.
This variable expands to the number of seconds since the shell was started. Assignment to this variable resets the count to the value assigned, and theexpanded value becomes the value assigned plus the number of secondssince the assignment.The number of seconds at shell invocation and the current time are alwaysdetermined by querying the system clock.If SECONDSis unset, it loses its special properties,even if it is subsequently reset.
In an interactive shell, the value is interpreted asthe number of seconds to wait for a line of input after issuingthe primary prompt.Bashterminates after waiting for that number of seconds if a completeline of input does not arrive.
If this option is present, or if no arguments remain after optionprocessing, then commands are read from the standard input.This option allows the positional parameters to be setwhen invoking an interactive shell or when reading inputthrough a pipe.
An interactive shell is one started without non-option arguments,unless -s is specified,without specifying the -c option, and whose input and output are bothconnected to terminals (as determined by isatty(3)), or onestarted with the -i option. See Interactive Shells, for moreinformation.
When Bash is invoked as an interactive login shell, or as anon-interactive shell with the --login option, it first reads andexecutes commands from the file /etc/profile, if that file exists.After reading that file, it looks for /.bash_profile,/.bash_login, and /.profile, in that order, and readsand executes commands from the first one that exists and is readable.The --noprofile option may be used when the shell is started toinhibit this behavior.
When an interactive shell that is not a login shell is started, Bashreads and executes commands from /.bashrc, if that file exists.This may be inhibited by using the --norc option.The --rcfile file option will force Bash to read andexecute commands from file instead of /.bashrc.
When Bash is started non-interactively, to run a shell script,for example, it looks for the variable BASH_ENV in the environment,expands its value if it appears there, and uses the expanded value asthe name of a file to read and execute. Bash behaves as if thefollowing command were executed: 2ff7e9595c
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