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A column of whitespace in the NEWS file was removed for consistent formatting. Most of the spelling errors were found with this codespell dictionary: https://github.com/orbitcowboy/codespell_dictionary (cherry picked from commit 0e36b17abe5609c461a3e4da7041eb0fdf9991b7)
1004 lines
33 KiB
HTML
1004 lines
33 KiB
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<TABLE border=0 align=center width=96%>
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<TBODY><TR><TD valign=top align=left>
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<!--INDEX--><!--/INDEX-->
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<P>
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<P><CENTER><FONT color=red><FONT face=courier><H3><A name="general">general</A></H3></FONT></FONT></CENTER>
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<DIV class=SH>
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<DL>
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<DT>What is KornShell?<DD>
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KornShell is a command and scripting language that is a superset of the System V UNIX shell,
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aka, BourneShell (or
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<EM>sh</EM>).
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<DT>What is ksh?<DD>
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ksh is the name of the program that implements the KornShell language.
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<DT>What is the history of ksh?<DD>
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ksh was written by David Korn at Bell Telephone Laboratories.
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David Korn is currently at AT&T Research.
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The first version of ksh was in 1983.
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It was the first shell to have command line editing with both emacs and vi style interaction.
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The 1986 version was the first to offer multibyte support.
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The 1988 version of ksh is the version that was adopted by System V Release 4 UNIX
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and was a source document for the IEEE POSIX and ISO shell standards.
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The 1993 version is a major rewrite of the 1988 version and focuses more on scripting.
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<DT>Where is the official description of the KornShell language?<DD>
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The Bolsky and Korn book,
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<EM>The KornShell Command and Programming Language</EM>,
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published by Prentice Hall, defines the 1988 version.
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The newer Bolsky and Korn book,
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<EM>The New KornShell Command and Programming Language</EM>,
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also published by Prentice Hall, describes the 1993 version.
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There are many new features since this book was published and
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the man page for ksh93 is kept up to date.
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<DT>What are the major new features of KornShell 1993?<DD>
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The only major new interactive features are key binding and tab completion.
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Major new language features are floating point arithmetic,
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associative arrays, complete ANSI-C printf, name reference
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variables, new expansion operators, dynamic loading of
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built-in commands, active variables, and compound variables.
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Active and compound variables allow shell variables to
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behave like objects. The ability to define types was added in 2009.
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In addition, ksh93 has been written to be
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extensible with an C language API for programming extensions.
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<DT>Are any further releases of ksh planned?<DD>
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Yes, the KornShell language and ksh implementation are in active development.
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Most of the focus will be on scripting and reusability.
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<DT>Why are newer release of ksh still called ksh93?<DD>
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We started the AST/ksh OpenSource release process in the late 90's.
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At that point ksh93 was the well-known name for ksh.
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The OpenSource release was finally granted in March 2000.
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No one has since volunteered to repeat that process for ksh<EM>XX</EM>.
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<DT>How can I determine the release or version of a particular ksh?<DD>
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The current version and release string may be accessed by
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<STRONG>${.sh.version}</STRONG>
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and
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<STRONG>$KSH_VERSION</STRONG>.
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The format is <STRONG>Version</STRONG> <EM>features</EM> 93<EM>version</EM>[-/+] <EM>release</EM>:
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<UL type=square>
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<LI>
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<EM>features</EM> --
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compile time features, typically enabled by <STRONG>SHOPT_</STRONG><EM>foo</EM> state variables in the
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ksh93 Makefile.
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A single letter represents each feature:
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<UL type=circle>
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<LI>
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<STRONG>A</STRONG>
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(<EM>SHOPT_AUDIT</EM>)
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<LI>
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<STRONG>B</STRONG>
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(<EM>SHOPT_BASH</EM>)
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bash compatibility mode.
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<LI>
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<STRONG>J</STRONG>
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(<EM>SHOPT_COSHELL</EM>)
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<STRONG>-lcoshell</STRONG> job pools.
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<LI>
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<STRONG>j</STRONG>
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(<EM>SHOPT_BGX</EM>)
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<LI>
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<STRONG>L</STRONG>
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(<EM>SHOPT_ACCT</EM>)
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<LI>
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<STRONG>M</STRONG>
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(<EM>SHOPT_MULTIBYTE</EM>)
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<LI>
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<STRONG>P</STRONG>
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(<EM>SHOPT_PFSH</EM>)
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<LI>
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<STRONG>R</STRONG>
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(<EM>SHOPT_REGRESS</EM>)
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</UL>
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<LI>
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<EM>version</EM>--
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a lower-case letter signifying major release points.
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An optional <STRONG>-</STRONG> following <EM>features</EM> signifies an alpha release.
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The first stable release has no <STRONG>-</STRONG>.
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An optional <STRONG>+</STRONG> signifies a stable release with bug patches and minor enhancements.
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<LI>
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<EM>release</EM>--
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the release date in <EM>YYYY-MM-DD</EM> form.
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This date corresponds to AST package and git repository releases.
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</UL>
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<STRONG>KSH_VERSION</STRONG>
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in a numeric context is an integer that encodes the release
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<EM>YYYYMMDD</EM>.
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<DT>What new features are planned for ksh?<DD>
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We are in the early stage of planning but the likely additions
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are namespaces, ability to read xml and json object into shell variables,
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and handling of queued signals.
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Support for multi-threading is also being considered.
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<DT>Is KornShell public domain?<DD>
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Yes, the language description is public domain and
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can be reimplemented.
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Some of the KornShell language features have been reimplemented
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in the GNU shell, bash, in zsh and mksh, and in pdksh, a public domain
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implementation.
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<DT>Is ksh public domain?<DD>
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No, earlier versions were owned by both AT&T and Novell.
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The 1993 version is owned by both Lucent and AT&T.
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<DT>Is source code available?<DD>
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Starting in March 2000, the ksh93 source is available
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as part of a larger collection of software called
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the ast-open software package which can be downloaded
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from the
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<A href="https://github.com/att/ast" target=_top>github page.</A>
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<DT>What are the licensing terms?<DD>
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The exact license terms can be found on the
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<A href="https://github.com/att/ast/blob/master/LICENSE.md" target=_top>licence page.</A>
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<DT>Does the license allow binaries to be freely redistributed?<DD>
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Yes, provided you make the license terms available to
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everyone you distribute binaries to.
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<DT>If I make changes to the code, do I have to make them public?<DD>
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No, you do not have to make them public.
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However, if you distribute the changes, you must allow us to be able
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to get these changes and distribute them along with the source.
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<DT>Why do some vendors still ship ksh88, not ksh93?<DD>
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Since ksh88 was included in System V release 4, most vendors
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have just included this version. However most Linux systems
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and Mac OS provide ksh93 version 's' or later. Solaris11 uses
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ksh93 as /bin/sh.
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<DT>Do you provide support for ksh?<DD>
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No, we will try to fix any bugs we hear about in future
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releases, but we do not provide any official support.
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<DT>Is ksh supported commercially?<DD>
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Software vendors that supply ksh with
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their systems typically support it for that system.
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<DT>What is pdksh and is it related to ksh or KornShell?<DD>
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pdksh is a public domain version of a UNIX shell that is
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unrelated to ksh.
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It supports most of the 1988 KornShell language features and some of the 1993 features.
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Some KornShell scripts will not run with pdksh.
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<DT>How is the MKS Toolkit KornShell related to KornShell?<DD>
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MKS Toolkit KornShell is a completely independent implementation
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that supports a subset of the 1988 KornShell language.
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<DT>What systems does ksh run on?<DD>
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ksh has been written to be portable.
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It has been ported to virtually run on every known UNIX system.
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In addition it runs on non-UNIX systems such as IBM's MVS using OpenEdition, and
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Microsoft's Windows 9X, Windows NT and Windows 2000.
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ksh is part of the UWIN (Unix for Windows)</A>
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software,
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<DT>Does ksh conform to the IEEE POSIX and ISO shell standard?<DD>
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The 1993 version should conform to the 1992 standard.
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At one point it had passed the test suite created by X/OPEN.
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<DT>Will KornShell 88 scripts run with KornShell 93?<DD>
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In almost all cases, the answer is yes.
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However, the IEEE POSIX and ISO standards required a few
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changes that could cause scripts to fail.
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There is a separate document that lists all known incompatibilities.
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<DT>Can ksh run as /bin/sh?<DD>
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We have installed ksh as /bin/sh on several systems without
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encountering any problems. It is /bin/sh on Solaris11.
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Our Linux systems use this instead of bash.
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</DL>
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</DIV>
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<P>
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<P><HR><CENTER><FONT color=red><FONT face=courier><H3><A name="interactive">interactive</A></H3></FONT></FONT></CENTER>
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<DIV class=SH>
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<DL>
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<DT>How do I get separate history files for shell?<DD>
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ksh uses a shared history file for all shells that
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use the same history file name.
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This means that commands entered in one window will be seen by
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shells in other windows.
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To get separate windows, the HISTFILE variable needs to be set to different name
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before the first history command is created.
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<DT>How do I get the time of day in my prompt?<DD>
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You can use printf with supports the %T format for time and date formatting.
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For example, the format %(%H:%M:%S)T specifies time in hour, minute, second
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format and if no argument is specified, the current time is used. Thus setting
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PS1='$(printf "%(%H:%M:%S)T" $' will output the time of day before the
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$ prompt.
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<DT>Why does the screen width not function correctly when non-printing characters are in my prompt?<DD>
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The shell computes the screen width by subtracting the width of the prompt from the screen width.
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To account for non-printing characters, for example escape sequences that display in the title
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bar, follow these characters with a carriage return.
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The shell starts recomputing the width after each carriage return.
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<DT>What is the PS4 prompt and how is it used?<DD>
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The PS4 prompt is evaluated and displayed before each line when
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running an execution trace.
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If unset, a + and a <space> will
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be output before each line in the trace.
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Putting '$LINENO' inside PS4 will cause the line number to be displayed.
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Putting '$SECONDS' in the PS4 prompt will cause the elapsed time
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to be displayed before each line.
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Note that single quotes are used to prevent the expansion from happening
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when PS4 is defined.
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<DT>How is keybinding done?<DD>
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ksh93 provides a KEYBD trap that gets executed whenever a key
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is entered from the keyboard.
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Using this trap, and the associative
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array feature of ksh93, a keybind function can easily be written
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which will map any entered key sequence to another key sequence.
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<DT>How do I get the arrow keys to work?<DD>
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Starting with the 'h' point release, on most keyboards you
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do not have to do anything to get the arrow keys to work.
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However, if they do not generate standard escape sequences,
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then you will have to use a keybinding function to get them
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to work.
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<DT>Does ksh support file name completion?<DD>
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Yes, it does.
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The default key binding is <ESC><ESC>
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however, starting with the 'g' point release, <TAB> also works
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for completion.
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<DT>Does ksh support command completion?<DD>
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If you perform completion on the first word of a command,
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ksh will do completion using aliases, functions, and commands.
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<DT>Is completion programmable?<DD>
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Yes, using the key binding mechanism, you can script the behavior
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of any key and therefore cause the current contents of any
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line to be replaced by any other line.
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<DT>Is there any way to get the command-line editor to go to more than a single line?<DD>
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The multiline option (now on by default) allows lines longer than the width
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of the screen to be displayed on multiple lines on the screen.
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Also in vi-mode, if you hit 'v' while in control mode, it will bring
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up a full screen version of vi on the current command.
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The command
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will execute when you exit vi.
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<DT>What is predictive editing?<DD>
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In 2010, a compile option was added that cause the shell to try to predict
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what you were trying to type by looking in the history file for all lines
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that matched and presenting them as a menu. Any line starting with # would
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use the characters you type to find matching lines from the history file.
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If you find the line you wanted, you can enter the number followed by
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<TAB> or newline. However bugs in earlier version led to core dumps.
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<DT>Can I use the shell line editor on other commands?<DD>
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The command ie, that comes along with shell, can be used
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to run line input oriented commands with command line editing.
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<DT>When I do echo $?, I am getting 267. What does this mean?<DD>
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ksh93 reports process that terminate with a signal as 256+signo.
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Earlier versions used 128+signo but this makes it impossible
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to distinguish from a command exit with that value.
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If you run
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<DIV class=FI>
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<PRE>
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kill -l $?
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</DIV>
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</PRE>
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on this signal number, it will give the the name of the signal
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that caused this exit.
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<DT>When I type builtin, I notice that some of these are full pathnames. What does this mean?<DD>
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Builtins that are not bound to pathnames are always searched
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for before doing a path search.
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Builtins that are bound
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to pathnames are only executed when the path search would
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bind to this pathname.
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<DT>What is a self generating man page?<DD>
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A self generating man page is one that is generated by the
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option parser within that command using an extended version
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of the getopts function.
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The man page can be generated in html,
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troff, or directly for the terminal.
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Most builtin commands
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in the shell have self generating man pages so that you
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can run for example,
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<STRONG>kill --man</STRONG>
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or
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<STRONG>kill --html</STRONG>
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to get
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the description of kill to the screen or as an html file.
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All self-documenting output is to the standard error,
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so you must redirect 2>... to capture the output.
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<P>
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This same method can also be used for shell scripts.
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Run
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<STRONG>getopts --man</STRONG>
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for more details.
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<DT>What is autoloading?<DD>
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Autoloading was a method used in ksh88, and still permitted in ksh93
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to declare that a name corresponded to a function.
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The function
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would be loaded and executed when first referenced.
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This was
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necessary since FPATH was always searched after PATH with ksh88
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and therefore if you defined a function whose name was the same
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as that of a program on your path, the program on your path
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would have been executed.
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With ksh93, when a pathname is
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encountered that is on PATH, but also is in FPATH, this directory
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is assumed to be a function directory.
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Thus, you can have
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function directories searched before program directories so
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that autoloading is no longer needed.
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<DT>Why does the output from 'time command 2> file' come out on the screen?<DD>
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The time command is a compound command in ksh and time is a reserved
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word It can be followed by any pipeline. Thus, redirections applied
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at the end are for the command, not to time itself. You can use
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time {...;} 2> file to capture the timing output to a file. Note,
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that with ksh, time works with all commands, for example,
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time for i; do xxx;done.
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<DT>When I run 'mv * ../elsewhere' I so that get '-ksh: mv: cannot execute [Arg list too long]', what causes this?<DD>
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UNIX systems have a limit to the space consumed by command arguments and
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environment variables when running commands that are not built into
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the shell. The configuration parameter ARG_MAX defines this limit.
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You can run 'getconf ARG_MAX' to find the limit for your system. Note
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that the shell expands * to the list of files in the current directory
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before running mv. In many case the xargs or tw command can be
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used to work around this problem by splitting the line into chunks
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and invoking the command. Another way to work around this limit
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is to make the command a builtin. On systems in which the cmd
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library is installed, you can invoke 'builtin -f cmd mv' to make
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mv a shell builtin in which case the line length limit no longer
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applies. Another alternative is to use a for loop and invoke
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the mv command for each file, for exampe,
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'for i in *;do mv $i ../elsewhere;done'.
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Starting with ksh93o+, a new feature was added to ksh to overcome
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this limit in some cases. If a command is preceded by
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'command -x', and it fails because there are two many arguments,
|
|
the command will be run multiple times with subsets of the arguments.
|
|
However, the change in ksh93o+ does not work in the above case
|
|
because the ../elsewhere is not used for each subset. This problem
|
|
was resolved starting in ksh93p so that
|
|
command -x mv * ../elsewhere
|
|
should work. Note that it is possible to do alias mv='command -x mv'
|
|
|
|
<DT>Is there any way to generate the list of .c files in the current directory and all the subdirectories?<DD>
|
|
|
|
Starting with ksh93o+, the globstar option (set -G or set -o globstar)
|
|
was added. With globstar enabled, ** by itself matches zero or more
|
|
directories or files, and **/ matches zero or more directories so that
|
|
**/*.c will match all .c files under the current directory.
|
|
|
|
<DT>Is there any way to prevent sending a HUP signal to a job when I log out if I didn't nohup the job?<DD>
|
|
|
|
Yes, the disown command tells ksh not to forward the HUP signal
|
|
to the specified jobs when it disconnects.
|
|
|
|
</DL>
|
|
</DIV>
|
|
|
|
<P>
|
|
<P><HR><CENTER><FONT color=red><FONT face=courier><H3><A name="programming">programming</A></H3></FONT></FONT></CENTER>
|
|
<DIV class=SH>
|
|
<DL>
|
|
|
|
<DT>What is the difference between * and @, for example, and ?<DD>
|
|
|
|
When used outside of "", they are equivalent.
|
|
However, within
|
|
double quotes, "$@" produces one argument for each positional
|
|
parameter, and "$* produces a single argument.
|
|
Note that "$@"
|
|
preserves arguments lists, whereas $* may not unless both
|
|
word splitting and pathname expansion are disabled.
|
|
|
|
<DT>Why do I need spaces around { and } but not around ( and )?<DD>
|
|
|
|
The characters ( and ) are shell metacharacters and are always
|
|
treated specially.
|
|
For historical reasons, { and } were
|
|
treated as reserved words and are only special as separate
|
|
words at locations in which a command can begin.
|
|
|
|
<DT>How do I get read to maintain the \ characters?<DD>
|
|
|
|
Use read -r instead.
|
|
|
|
<DT>How can I a write a ksh script that responds directly to each character so that you user just has to enter y, not y<return>?<DD>
|
|
|
|
There are two ways to do this.
|
|
The easiest is to use
|
|
<DIV class=FI>
|
|
<PRE>
|
|
read -n1 x
|
|
</DIV>
|
|
</PRE>
|
|
Alternatively, you could do
|
|
<DIV class=FI>
|
|
<PRE>
|
|
function keytrap
|
|
{
|
|
.sh.edchar=${sh.edchar}$'
|
|
}
|
|
trap keytrap KEYBD
|
|
</DIV>
|
|
</PRE>
|
|
and then
|
|
<DIV class=FI>
|
|
<PRE>
|
|
read x
|
|
</DIV>
|
|
</PRE>
|
|
|
|
<DT>What is the purpose of $'...'?<DD>
|
|
|
|
The $'...' string literal syntax was added to ksh93 to solve the problem
|
|
of entering special characters in scripts.
|
|
It uses
|
|
ANSI-C rules to translate the string between the '...'.
|
|
It would have been cleaner to have all "..." strings handle
|
|
ANSI-C escapes, but that would not be backward compatible.
|
|
|
|
<DT>What is the -n option used for?<DD>
|
|
|
|
You should always run ksh -n on each script you write.
|
|
The -n
|
|
option will check for syntax errors on paths that might not
|
|
even be checked when you run the script.
|
|
It also produces
|
|
a number of warning messages.
|
|
|
|
<DT>Why are both `...` and $(...) used for command substitution?<DD>
|
|
|
|
The `...` method has some rather strange quoting rules
|
|
and does not nest easily.
|
|
$(...) was added to ksh88 to
|
|
make command substitution easy to use.
|
|
`...` is provided
|
|
for backwards compatibility only.
|
|
|
|
<DT>How can I tell if all the commands of a pipeline have succeeded?<DD>
|
|
|
|
The pipefail option was added to the 'g' point release of ksh93.
|
|
With pipefail set, a pipeline will fail if any element of the
|
|
pipeline fails.
|
|
The exit status will be that of the first
|
|
command that has failed.
|
|
|
|
<DT>What is the difference between [...] and [[...]]?<DD>
|
|
|
|
The [[...]] is processed as part of the shell grammar
|
|
whereas [...] is processed like any other command.
|
|
Operators and operands are detected when the command is
|
|
read, not after expansions are performed.
|
|
The shell does not
|
|
do word splitting or pathname generation inside [[...]].
|
|
This allows patterns to be specified for string matching
|
|
purposes. You should use [[...]] instead of [...] and test.
|
|
|
|
<DT>How come [[ $foo == $bar ]] is true and [[ $bar == $foo ]] is false?<DD>
|
|
|
|
The == operator is not symmetrical.
|
|
It takes a string on the left
|
|
and a pattern on the right.
|
|
However, if you double quote the right
|
|
hand side, which removes the special meaning of pattern match
|
|
characters, then this becomes a string comparison so that
|
|
[[ "$foo" == "bar" ]] and [[ "$bar" == "$foo" ]] are equivalent.
|
|
|
|
<DT>Why does ksh93 have print since echo already exists is is widely used?<DD>
|
|
|
|
The behavior of echo varies from system to system.
|
|
The POSIX standard does not define the behavior of echo when
|
|
the first argument beings with a - or when any argument
|
|
contains a character.
|
|
This makes echo pretty useless for
|
|
use in portable scripts.
|
|
|
|
<DT>What is $bar after running 'echo foo | read bar'?<DD>
|
|
|
|
The answer is foo.
|
|
ksh runs the last component of a pipeline
|
|
in the current process.
|
|
Some shells run it as a subshell
|
|
as if you had invoked it as echo foo | (read bar).
|
|
|
|
<DT>How can I access a substring of a variable?<DD>
|
|
|
|
The syntax ${varname:offset:len} can be used to generate
|
|
the string of length len starting at the the specified
|
|
offset. String offsets start at 0. If :len is omitted,
|
|
then the remainder of the string will be used. Both offset
|
|
and len can be arithmetic expressions. A negative offset is
|
|
subtracted from the last offset.
|
|
|
|
<DT>What is the difference between ((expr)) and $((expr))?<DD>
|
|
|
|
((expr)) is a command that evaluates an arithmetic expression.
|
|
The exit status of this command is 0 if the expression
|
|
evaluates to non-zero and is 1 if it evaluates to 0.
|
|
0 is an string expansion that expands to a string
|
|
representation of the value of this arithmetic expression.
|
|
It can be used anywhere a variable substitution is permitted.
|
|
<P>
|
|
|
|
<DT>What is the difference between $((x*y)) and $(($x*$y))?<DD>
|
|
|
|
In the first case the value of x and the value of y are multiplied
|
|
together, and then their result is converted to a string.
|
|
In the
|
|
second case variables $x, *, and $y are concatenated to form
|
|
an arithmetic expression which is then evaluated.
|
|
This can
|
|
yield different results, for example,
|
|
<DIV class=FI>
|
|
<PRE>
|
|
x=2+3 y=4+5
|
|
print $((x*y)) \$(($x*$y))
|
|
45 19
|
|
When x and y are numeric the first form is recommended for better
|
|
performance.
|
|
</DIV>
|
|
</PRE>
|
|
|
|
<DT>How do I handle filenames with spaces in them?<DD>
|
|
|
|
To be POSIX conforming, ksh has to do word splitting and
|
|
pathname expansion the results of substitutions.
|
|
You can
|
|
enclose variable substitutions in "..." to prevent both
|
|
word splitting and pathname expansion.
|
|
Alternatively,
|
|
you can disable word splitting by setting IFS='' and
|
|
pathname generation with set -o noglob.
|
|
|
|
<DT>What are active variables?<DD>
|
|
|
|
By default shell variables are passive.
|
|
They hold values
|
|
given to them on assignment, and return values on reference.
|
|
Active variables allow the assignment and reference (and
|
|
other actions) be controlled by functions specific to that
|
|
variable.
|
|
At the shell level, a 'get', 'set', or 'unset'
|
|
shell function can be defined for any variable to make them
|
|
active, so that the function foo.set will be invoked whenever
|
|
the variable foo is assigned a value.
|
|
At the C interface
|
|
level, several functions can be stacked together for an
|
|
active variable.
|
|
|
|
<DT>What is the difference between function name and name()?<DD>
|
|
|
|
In ksh88 these were the same.
|
|
However, the POSIX standard
|
|
choose foo() for functions and defined System V Release 2
|
|
semantics to them so that there are no local variables
|
|
and so that traps are not scoped.
|
|
ksh93 keeps the ksh88
|
|
semantics for functions defined as function name, and
|
|
has changed the name() semantics to match the POSIX
|
|
semantics.
|
|
Clearly,
|
|
<STRONG>function</STRONG>
|
|
<EM>name</EM>
|
|
is more useful.
|
|
|
|
<DT>What is the naming conventions for files in FPATH and can one file contain more than one function definition?<DD>
|
|
|
|
You can have more than one function defined in each file defined
|
|
in FPATH and all of them will be added to the list of known
|
|
functions. Any commands placed in this file outside of function
|
|
definitions will be invoked first. The name of the file must be
|
|
that of the first function you invoke. If you have several functions
|
|
defined in one file, then you should create a link to each of the
|
|
function names that can potentially be invoked first.
|
|
|
|
<DT>What are name reference variables and how are they used?<DD>
|
|
|
|
Reference variables are variables in which all references
|
|
and assignments refer to the variable that they reference.
|
|
For example,
|
|
<DIV class=FI>
|
|
<PRE>
|
|
typeset -n name=$1
|
|
name=value
|
|
</DIV>
|
|
</PRE>
|
|
is equivalent to
|
|
<DIV class=FI>
|
|
<PRE>
|
|
eval \$1='value'
|
|
</DIV>
|
|
</PRE>
|
|
References are most useful for passing arguments such as
|
|
arrays to functions.
|
|
|
|
<DT>If i=1 and var1=some value, how do I print var$i to get its value?<DD>
|
|
|
|
Either use
|
|
<DIV class=FI>
|
|
<PRE>
|
|
eval print var\$i
|
|
</DIV>
|
|
</PRE>
|
|
or
|
|
<DIV class=FI>
|
|
<PRE>
|
|
typeset -n x=var$i
|
|
print $x
|
|
</DIV>
|
|
</PRE>
|
|
|
|
<DT>How can I shift the elements of an array?<DD>
|
|
|
|
The shift special builtin-command only works for positional
|
|
parameters.
|
|
However, noting that array subscripts start at 0, you can use
|
|
<DIV class=FI>
|
|
<PRE>
|
|
typeset -A name "${name[@]:1}"
|
|
</DIV>
|
|
</PRE>
|
|
to shift the array.
|
|
|
|
<DT>Why are the braces required with array references, e.g. ${x[1]}?<DD>
|
|
|
|
It would be nice to do $x[1], but the POSIX shell would expand $x
|
|
and then search for the file pattern resulting by concatenating [1].
|
|
ksh is POSIX compatible.
|
|
|
|
<DT>How do I get the list of subscript names for an associative array?<DD>
|
|
|
|
The prefix operator ! in variable expansions can be used to get names.
|
|
To get the names of subscripts for an array, associative
|
|
or indexed, use ${!var[@]}.
|
|
|
|
<DT>How do I do global substitutions on the contents of shell variables?<DD>
|
|
|
|
Use // instead of / for global substitution, ${var//aa/bb} will
|
|
expand to the value of with each "aa" replace by "bb".
|
|
|
|
<DT>How can I convert %XX values to ascii?<DD>
|
|
|
|
You can convert this to a sequence of ANSI C strings and then eval that
|
|
string, for example suppose the variable 'foo' contains %XX strings, then
|
|
<DIV class=FI>
|
|
<PRE>
|
|
eval print -r -- "\$'${foo//'%'@(??)/'\x\1"'\$'"}'"
|
|
</DIV>
|
|
</PRE>
|
|
will print out the string in ascii.
|
|
|
|
<DT>I want to use exec to open a file. How do I prevent the script from exiting if the exec fails?<DD>
|
|
|
|
If you run
|
|
<DIV class=FI>
|
|
<PRE>
|
|
command exec ... || error ...
|
|
</DIV>
|
|
</PRE>
|
|
then error will be executed if the exec fails, but the script
|
|
will not terminate.
|
|
The command builtin will prevent the shell
|
|
from exiting when special built-ins fail.
|
|
|
|
<DT>How do I execute a builtin inside a function of the same name?<DD>
|
|
|
|
You use the command builtin for this.
|
|
For example,
|
|
<DIV class=FI>
|
|
<PRE>
|
|
function cd
|
|
{
|
|
command cd "$@" && title "$PWD"
|
|
}
|
|
</DIV>
|
|
</PRE>
|
|
will run the builtin command cd from within the function cd
|
|
rather than calling the function cd recursively.
|
|
|
|
<DT>How are variables scoped in ksh?<DD>
|
|
|
|
The scoping of variables was not defined for ksh88 but in ksh93
|
|
static scoping was specified.
|
|
For example the output from
|
|
<DIV class=FI>
|
|
<PRE>
|
|
function f1
|
|
{
|
|
print foo=$foo
|
|
}
|
|
function f2
|
|
{
|
|
typeset foo=local
|
|
f1
|
|
}
|
|
foo=global
|
|
f2
|
|
</DIV>
|
|
</PRE>
|
|
will be "global".
|
|
To get f2 to cause f1 to print the local
|
|
value of foo, f2 can run "foo=$foo f1" instead.
|
|
|
|
<DT>Can you write a self reproducing program in KornShell?<DD>
|
|
|
|
Yes, the following program is self reproducing.
|
|
Any shorter ones?
|
|
<DIV class=FI>
|
|
<PRE>
|
|
n="
|
|
" q="'" x="cat <<-!" y=! z='n="$n" q="$q" x="$x" y=$y z=$q$z$q$n$x$n$z$n$y'
|
|
cat <<-!
|
|
n="$n" q="$q" x="$x" y=$y z=$q$z$q$n$x$n$z$n$y
|
|
!
|
|
</DIV>
|
|
</PRE>
|
|
|
|
</DL>
|
|
</DIV>
|
|
|
|
<P>
|
|
<P><HR><CENTER><FONT color=red><FONT face=courier><H3><A name="redirections">redirections</A></H3></FONT></FONT></CENTER>
|
|
<DIV class=SH>
|
|
<DL>
|
|
|
|
<DT>How do I redirect both standard input and standard output to a file?<DD>
|
|
|
|
Add the following redirections to the command.
|
|
> file 2> &1.
|
|
This will redirect standard output (file descriptor 1) to "file" and
|
|
standard error (file descriptor 2) to the same place as file descriptor 1.
|
|
ksh redirection allows you to redirect any single digit file descriptor
|
|
by putting the descriptor number in front of the redirection operator
|
|
with no intervening space.
|
|
|
|
<DT>Is there a way for the shell to pick the file number when I open a file?<DD>
|
|
|
|
Yes, a redirection operator operator can be preceded by {n} without any
|
|
intervening space where n is the name of a variable. The file descriptor
|
|
will be placed in variable n.
|
|
|
|
<DT>How do I connect to a socket from a shell script?<DD>
|
|
|
|
exec 3<> /dev/tcp/hostname/portnum
|
|
will open a tcp connection to portnum on hostname for
|
|
reading and writing on file descriptor 3.
|
|
You can then
|
|
use read and print statements with file descriptor 3,
|
|
or redirection operators <&3 or >&3 to use these connections.
|
|
|
|
<DT>How do I seek to a given location in a file?<DD>
|
|
|
|
The redirection operators <# and ># allow you to seek to a specified
|
|
location in a file. The operator can be followed by an arithmetic
|
|
expression contained in ((...)). The variables CUR and EOF can be used
|
|
in the arithmetic expression to get relative locations or locations
|
|
relative to the end of file respectively.
|
|
Alternatively, <# and ># can be followed by a shell pattern. In this
|
|
case, the file will be positioned to beginning of the next line
|
|
containing this pattern.
|
|
|
|
<DT>What is the the <<< redirection operator?<DD>
|
|
|
|
It denotes a here-document in which the document is contained the
|
|
argument that follows <<< and therefore there is no delimiter.
|
|
|
|
<DT>What is the the >; redirection operator?<DD>
|
|
|
|
This operator writes the output into a temporary file in the same
|
|
directory as the file specified after >;. If the command completes
|
|
successfully, then the the file is replaced. Otherwise, the
|
|
original file is unchanged and the temporary file removed.
|
|
|
|
<DT>What is the the <>; redirection operator?<DD>
|
|
|
|
The file is opened for reading and writing as with <>. However,
|
|
when the file is closed it is truncated to the its current location.
|
|
|
|
</DL>
|
|
</DIV>
|
|
|
|
<P>
|
|
<P><HR><CENTER><FONT color=red><FONT face=courier><H3><A name="extensions">extensions</A></H3></FONT></FONT></CENTER>
|
|
<DIV class=SH>
|
|
<DL>
|
|
|
|
<DT>Is there a shell compiler?<DD>
|
|
|
|
There is a separate command named shcomp that will convert
|
|
a script into an intermediate machine independent form.
|
|
The shell will detect this format whenever it runs a script and execute
|
|
directly from this intermediate format.
|
|
|
|
<DT>What is the advantage of making commands built-in?<DD>
|
|
|
|
The startup time is reduced by a couple of orders of magnitude.
|
|
In addition, built-in commands can access ksh internals.
|
|
|
|
<DT>What is the disadvantage of making commands built-in?<DD>
|
|
|
|
Errors in these built-ins can cause the shell to crash.
|
|
|
|
<DT>How do I add built-in commands?<DD>
|
|
|
|
There are two ways to do this.
|
|
One is write a shared library
|
|
with functions whose names are b_xxxx where xxxx is the name of
|
|
the builtin.
|
|
The function b_xxxx takes three arguments.
|
|
The first
|
|
two are the same as a mail program.
|
|
The third parameter is
|
|
a pointer argument which will point to the current shell context.
|
|
The second way is to write a shared library with a function named
|
|
lib_init().
|
|
This function will be called with an argument of 0
|
|
after the library is loaded.
|
|
This function can add built-ins
|
|
with the sh_addbuiltin() API function.
|
|
In both cases, the
|
|
library is loaded into the shell with the "builtin" utility.
|
|
|
|
<DT>Can ksh93 be embedded?<DD>
|
|
|
|
Yes, ksh93 can be compiled as a shared or dynamically linked
|
|
library which can be embedded into applications.
|
|
There is
|
|
an API for interfacing to shell variables and to several of
|
|
the internal shell functions.
|
|
|
|
<DT>Can I write GUI applications with ksh?<DD>
|
|
|
|
There are two extensions to ksh that can be used to write
|
|
GUI applications as shell script.
|
|
One is dtksh which
|
|
was written by Steve Pendergrast at Novell and is
|
|
included with the Common Desktop Environment, CDE.
|
|
The other is
|
|
tksh which was written by Jeff Korn.
|
|
tksh combines the tk graphics
|
|
package with ksh93 and reimplements the tcl language
|
|
as an extension so that both tcl and ksh scripts
|
|
can run in the same address space.
|
|
The source for tksh
|
|
is included in the ast-open package.
|
|
|
|
</DL>
|
|
</DIV>
|
|
<TABLE cellpadding=4>
|
|
<TR>
|
|
<TD bgcolor=teal><A href='#' onclick='FAQ_mark("show")'><FONT color="#FFD87D">show all answers</FONT></A></TD>
|
|
<TD bgcolor=teal><A href='#' onclick='FAQ_mark("hide")'><FONT color="#FFD87D">hide all answers</FONT></A></TD>
|
|
</TR>
|
|
</TABLE>
|
|
<P>
|
|
<HR>
|
|
<TABLE border=0 align=center width=96%>
|
|
<TR>
|
|
<TD align=left></TD>
|
|
<TD align=center></TD>
|
|
<TD align=right>June 19, 2012</TD>
|
|
</TR>
|
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</TABLE>
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