mirror of https://github.com/tLDP/LDP
Removed some <para> tags from within <listitem> elements. Shortened the text in
some <screen> and <programlisting> elements.
This commit is contained in:
franl
parent
a796880ad6
commit
803a0b1e57
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@ -5,18 +5,17 @@ IMPORTANT! Before doing any CVS commits, change the DTD location from:
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|||
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"file:///cygdrive/c/franl/work/ldp/dtd-4.2/docbookx.dtd"
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to:
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"http://docbook.org/xml/4.3/docbookx.dtd"
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"http://docbook.org/xml/4.2/docbookx.dtd"
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-->
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://docbook.org/xml/4.3/docbookx.dtd"
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[
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"http://docbook.org/xml/4.2/docbookx.dtd"
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[
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<!ENTITY ldp "Linux Documentation Project">
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<!ENTITY ldpurl "http://www.tldp.org/">
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<!ENTITY thisurl "&ldpurl;HOWTO/Intro-Bash-Scripting-HOWTO.html">
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<!ENTITY gfdlurl "http://www.gnu.org/copyleft/fdl.html">
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]
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>
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]>
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<!--
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************************************************************************
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@ -103,7 +102,7 @@ Maintainers: Francis Litterio <franl@world.std.com>,
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You can always find the latest version of this HOWTO at the <ulink
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url="&ldpurl;">Linux Documentation Project</ulink> at this location:
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</para>
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<blockquote>
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<para><ulink url="&thisurl;">&thisurl;</ulink>.</para>
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</blockquote>
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@ -120,7 +119,7 @@ Maintainers: Francis Litterio <franl@world.std.com>,
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containing commands that are executed by Bash. This HOWTO is an
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introduction to writing Bash scripts.
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</para>
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<para>
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This HOWTO is written for anyone who wants to begin writing Bash scripts
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but who has no prior scripting experience. You do not have to be a
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@ -159,11 +158,11 @@ Maintainers: Francis Litterio <franl@world.std.com>,
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<!-- Please scramble addresses; help prevent spam/email harvesting -->
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<itemizedlist spacing="compact">
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<listitem><para>Nathan Hurst</para></listitem>
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<listitem><para>Jon Abbott</para></listitem>
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<listitem><para>Felix Hudson</para></listitem>
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<listitem><para>Kees van den Broek</para></listitem>
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<listitem><para>Andreas Beck</para></listitem>
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<listitem>Nathan Hurst</listitem>
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<listitem>Jon Abbott</listitem>
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<listitem>Felix Hudson</listitem>
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<listitem>Kees van den Broek</listitem>
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<listitem>Andreas Beck</listitem>
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</itemizedlist>
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</sect2>
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@ -206,7 +205,7 @@ Maintainers: Francis Litterio <franl@world.std.com>,
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<sect1 id="sect-getting-started">
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<title>Getting Started</title>
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<sect2 id="sect-what-you-should-know">
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<title>What You Should Already Know</title>
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@ -214,44 +213,36 @@ Maintainers: Francis Litterio <franl@world.std.com>,
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This HOWTO assumes you know the following things about using Bash
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interactively.
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</para>
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<itemizedlist>
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<listitem>
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<para>
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You understand the purpose of the Bash startup files
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<filename>.bash_profile</filename> and <filename>.bashrc</filename>
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in your home directory, even if you have not editted them yourself.
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</para>
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You understand the purpose of the Bash startup files
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<filename>.bash_profile</filename> and <filename>.bashrc</filename>
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in your home directory, even if you have not editted them yourself.
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</listitem>
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<listitem>
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<para>
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You understand the purpose of the environment variables
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<envar>HOME</envar> and <envar>PATH</envar>.
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</para>
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You understand the purpose of the environment variables
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<envar>HOME</envar> and <envar>PATH</envar>.
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</listitem>
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<listitem>
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<para>
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You understand the purpose of basic shell metacharacters, such as
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"<computeroutput>*</computeroutput>",
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"<computeroutput>?</computeroutput>", and
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"<computeroutput>~</computeroutput>".
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</para>
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You understand the purpose of basic shell metacharacters, such as
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"<computeroutput>*</computeroutput>",
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"<computeroutput>?</computeroutput>", and
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"<computeroutput>~</computeroutput>".
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</listitem>
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<listitem>
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<para>
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You understand how to run commands in the background by appending a
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"<computeroutput>&</computeroutput>" to the end of a command.
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</para>
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You understand how to run commands in the background by appending a
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"<computeroutput>&</computeroutput>" to the end of a command.
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</listitem>
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</itemizedlist>
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</sect2>
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<sect2 id="sect-what-is-bash">
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<title>What and Where is Bash?</title>
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<para>
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Bash is a <firstterm>shell</firstterm>, which is a program that reads
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commands and executes them. Sometimes, the commands that Bash reads
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@ -266,7 +257,7 @@ Maintainers: Francis Litterio <franl@world.std.com>,
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each line of the script file from top to bottom, executing each command
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as if it had been typed on the keyboard.
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</para>
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<para>
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Where is the Bash shell? On GNU/Linux systems, you'll always find
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Bash in <filename>/bin/bash</filename>. On commerical UNIX systems, such
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@ -275,7 +266,7 @@ Maintainers: Francis Litterio <franl@world.std.com>,
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directly, but you need to know where Bash is located on your system so
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that you can write the very first line of your Bash scripts correctly.
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</para>
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<para>
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Often, you can find where Bash is located on a UNIX system by typing
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"<computeroutput><command>which
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@ -285,13 +276,13 @@ Maintainers: Francis Litterio <franl@world.std.com>,
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that doesn't work, try this
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<computeroutput><command>find</command></computeroutput> command:
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</para>
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<blockquote>
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<para>
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<computeroutput>find / -type f -name bash 2>/dev/null</computeroutput>
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</para>
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</blockquote>
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<para>
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If that doesn't work, ask your system administrator or local guru for
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help. It's possible that you do not have Bash installed on your system.
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@ -416,25 +407,21 @@ Hello world
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<orderedlist>
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<listitem>
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<para>
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Change the permissions on the script to allow you to execute it.
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This can be done with the command
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"<computeroutput><command>chmod u+x hello</command></computeroutput>".
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You don't have to grant execute permission just to yourself. The
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command
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"<computeroutput><command>chmod ugo+x hello</command></computeroutput>"
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allows everyone to execute your script. See the man page for the
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<computeroutput><command>chmod</command></computeroutput> command
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for more information.
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</para>
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Change the permissions on the script to allow you to execute it.
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This can be done with the command
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"<computeroutput><command>chmod u+x hello</command></computeroutput>".
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You don't have to grant execute permission just to yourself. The
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command
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"<computeroutput><command>chmod ugo+x hello</command></computeroutput>"
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allows everyone to execute your script. See the man page for the
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<computeroutput><command>chmod</command></computeroutput> command
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for more information.
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</listitem>
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<listitem id="item-dir-path">
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<para>
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Make sure that the directory containing the script is one of the
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directories listed in the value of your <envar>PATH</envar>
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environment variable.
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</para>
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Make sure that the directory containing the script is one of the
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directories listed in the value of your <envar>PATH</envar>
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environment variable.
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</listitem>
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</orderedlist>
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@ -442,46 +429,38 @@ Hello world
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A good way to satisfy the requirement in item #<xref
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linkend="item-dir-path"/> above is to do this:
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</para>
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<orderedlist>
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<listitem>
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<para>
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Create a directory named "<filename>bin</filename>" under your home
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directory. You can do this with the command
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"<computeroutput><command>mkdir $HOME/bin</command></computeroutput>".
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</para>
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</listitem>
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<listitem>
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<para>
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Move the script to that directory. You can do this with the command
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"<computeroutput><command>mv hello $HOME/bin</command></computeroutput>".
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</para>
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</listitem>
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<listitem>
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<para>
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List the full pathname of that directory in the value of your
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<envar>PATH</envar> environment variable (We cover variables in more
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detail in <xref linkend="sect-variables"/>). You can do this by
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putting the following line into your interactive Bash startup script
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(which is the file <filename>.bashrc</filename> in your home
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directory):
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<blockquote>
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<para>
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<computeroutput>PATH="$HOME/bin:$PATH"</computeroutput>
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</para>
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</blockquote>
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</para>
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Create a directory named "<filename>bin</filename>" under your home
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directory. You can do this with the command
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"<computeroutput><command>mkdir $HOME/bin</command></computeroutput>".
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</listitem>
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<listitem>
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<para>
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Terminate your shell, and start a new one. You have to do this
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because the changes to your <filename>.bashrc</filename> file only
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take effect in shells started after you save the changes.
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</para>
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Move the script to that directory. You can do this with the command
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"<computeroutput><command>mv hello $HOME/bin</command></computeroutput>".
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</listitem>
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<listitem>
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List the full pathname of that directory in the value of your
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<envar>PATH</envar> environment variable (We cover variables in more
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detail in <xref linkend="sect-variables"/>). You can do this by
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putting the following line into your interactive Bash startup script
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(which is the file <filename>.bashrc</filename> in your home
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directory):
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<blockquote>
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<para>
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<computeroutput>PATH="$HOME/bin:$PATH"</computeroutput>
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</para>
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</blockquote>
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</listitem>
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<listitem>
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Terminate your shell, and start a new one. You have to do this
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because the changes to your <filename>.bashrc</filename> file only
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take effect in shells started after you save the changes.
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</listitem>
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</orderedlist>
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@ -547,7 +526,7 @@ Hello world
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good analogy is to think of a chef cooking a meal by reading a recipe. In
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this case, your script is the recipe, and Bash is the chef.
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</para>
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<para>
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The first line of your script must specify the full pathname of the Bash
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shell immediately after the characters
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@ -584,7 +563,7 @@ Hello world
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(<computeroutput>#!/bin/bash</computeroutput>)? What happens when Bash
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reads and executes that line?
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</para>
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<para>
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The answer is: nothing. The text between a
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"<computeroutput>#</computeroutput>" character and the end of the same
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@ -690,7 +669,7 @@ Hello world
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ignores blank lines, so you can use them to make your script more
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readable.
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</para>
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<para>
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<blockquote>
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<example id="ex-comments">
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@ -698,14 +677,15 @@ Hello world
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<programlisting>
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#!/bin/bash
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# This script is an example of using comments.
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echo Hello world # This comment shares a line with a command!
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echo Hello world # This comment shares a line with a command!
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# The next line does _not_ contain a comment! Do you see why?
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# The next line does _not_ contain a comment!
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echo Hello#world
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# This is also a comment. The "#" doesn't have to be in the leftmost
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# column. Compare the next echo command with the previous echo command.
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# One little space can make a big difference!
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# This is also a comment. The "#" doesn't have to be
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# in the leftmost column. Compare the next echo
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# command with the previous echo command. One little
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# space can make a big difference!
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echo Hello #world
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</programlisting>
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</example>
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@ -784,7 +764,7 @@ Hello
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<para>
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||||
Let's look at each one in turn.
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</para>
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<sect2 id="sect-double-quote">
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<title>Double Quotes</title>
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@ -795,7 +775,7 @@ Hello
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one word. For instance, if you need to refer to a file that has spaces in
|
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its name, you can use double quotes, as follows:
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</para>
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<para>
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<blockquote>
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<programlisting>
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@ -842,7 +822,7 @@ cat "meeting agenda.txt"
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happens because you can use double quotes to group words that span a
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newline character. Try this command in your interactive shell:
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</para>
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<para>
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<blockquote>
|
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<programlisting>
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|
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@ -889,7 +869,7 @@ scriptname: line 3: unexpected EOF while looking for matching `"'
|
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certain metacharacters. If you want your script to output an asterisk,
|
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you might attempt to do it with this command:
|
||||
</para>
|
||||
|
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|
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<para>
|
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<blockquote>
|
||||
<programlisting>
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@ -897,7 +877,7 @@ echo *
|
|||
</programlisting>
|
||||
</blockquote>
|
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</para>
|
||||
|
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<para>
|
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But the above command outputs the names of all files and directories in
|
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the script's current working directory, which is not what you intended.
|
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|
|
@ -925,7 +905,7 @@ echo "*"
|
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metacharacter. Let's be clear exactly which metacharacters double quotes
|
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escape. Double quotes escape the following Bash metacharacters.
|
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</para>
|
||||
|
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|
||||
<itemizedlist>
|
||||
<listitem>
|
||||
<para>
|
||||
|
|
@ -934,25 +914,25 @@ echo "*"
|
|||
<computeroutput>[</computeroutput>...<computeroutput>]</computeroutput>
|
||||
</para>
|
||||
</listitem>
|
||||
|
||||
|
||||
<listitem>
|
||||
<para>
|
||||
The home directory character: <computeroutput>~</computeroutput>
|
||||
</para>
|
||||
</listitem>
|
||||
|
||||
|
||||
<listitem>
|
||||
<para>
|
||||
Single quotes: <computeroutput>'</computeroutput>...<computeroutput>'</computeroutput>
|
||||
</para>
|
||||
</listitem>
|
||||
|
||||
|
||||
<listitem>
|
||||
<para>
|
||||
The background job creation character: <computeroutput>&</computeroutput>
|
||||
</para>
|
||||
</listitem>
|
||||
|
||||
|
||||
<listitem>
|
||||
<para>
|
||||
I/O Redirection characters: <computeroutput>></computeroutput>,
|
||||
|
|
@ -965,7 +945,7 @@ echo "*"
|
|||
</para>
|
||||
</listitem>
|
||||
</itemizedlist>
|
||||
|
||||
|
||||
<para>
|
||||
From this list, you can see that the double quote metacharacter does not
|
||||
escape itself. What if you want to output some text surrounded by double
|
||||
|
|
@ -973,7 +953,7 @@ echo "*"
|
|||
that the output of the script includes double quote characters? A command
|
||||
of this form doesn't work:
|
||||
</para>
|
||||
|
||||
|
||||
<para>
|
||||
<blockquote>
|
||||
<programlisting>
|
||||
|
|
@ -1020,16 +1000,16 @@ echo Now type ""start-backup"".
|
|||
different quote characters is that you can use one kind of quote character
|
||||
to escape the other, as <xref linkend="ex-mixing-quotes"/> shows.
|
||||
</para>
|
||||
|
||||
|
||||
<para>
|
||||
<blockquote>
|
||||
<example id="ex-mixing-quotes">
|
||||
<title>Mixing Single and Double Quotes</title>
|
||||
|
||||
|
||||
<programlisting>
|
||||
#!/bin/bash
|
||||
# This script shows how you can mix single and double quotes, using one kind to
|
||||
# escape the other kind.
|
||||
# This script shows how you can mix single and double
|
||||
# quotes, using one kind to escape the other kind.
|
||||
|
||||
echo "'This text is surrounded by single quotes.'"
|
||||
echo '"This text is surrounded by double quotes."'
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||||
|
|
@ -1042,7 +1022,7 @@ echo "Welcome to Frodo's Place."
|
|||
<para>
|
||||
The output of the above script is:
|
||||
</para>
|
||||
|
||||
|
||||
<blockquote>
|
||||
<para>
|
||||
<screen>
|
||||
|
|
@ -1210,7 +1190,7 @@ Welcome to Frodo's Place!
|
|||
|
||||
<sect2 id="sect-using">
|
||||
<title>Using Variables</title>
|
||||
|
||||
|
||||
<para>
|
||||
<xref linkend="ex-variable-assignment0"/> shows how to assign a string of
|
||||
characters to a variable.
|
||||
|
|
@ -1319,16 +1299,16 @@ CARPLURAL="${CARMODEL}s"
|
|||
A common task is to append (or prepend) a string to the current value of
|
||||
a variable. <xref linkend="ex-variable-append"/> shows how to do each.
|
||||
</para>
|
||||
|
||||
|
||||
<para>
|
||||
<blockquote>
|
||||
<example id="ex-variable-append">
|
||||
<title>Appending and Prepending Text to a Variable's Value</title>
|
||||
<programlisting>
|
||||
CUSTOMER_NAME="Fred"
|
||||
CUSTOMER_NAME="$CUSTOMER_NAME Smith" # Appends a string.
|
||||
CUSTOMER_NAME="Mr. $CUSTOMER_NAME" # Prepends a string.
|
||||
echo "$CUSTOMER_NAME" # Output is: Mr. Fred Smith
|
||||
CUSTOMER_NAME="$CUSTOMER_NAME Smith" # Appends a string.
|
||||
CUSTOMER_NAME="Mr. $CUSTOMER_NAME" # Prepends a string.
|
||||
echo "$CUSTOMER_NAME" # Output is: Mr. Fred Smith
|
||||
</programlisting>
|
||||
</example>
|
||||
</blockquote>
|
||||
|
|
@ -1399,7 +1379,7 @@ echo "$CUSTOMER_NAME" # Output is: Mr. Fred Smith
|
|||
</para>
|
||||
</listitem>
|
||||
</varlistentry>
|
||||
|
||||
|
||||
<varlistentry>
|
||||
<term><varname>HOME</varname></term>
|
||||
<listitem>
|
||||
|
|
@ -1431,7 +1411,7 @@ echo "$CUSTOMER_NAME" # Output is: Mr. Fred Smith
|
|||
provides I/O redirection, but the syntax differs between various shells.
|
||||
Naturally, we'll cover the Bash syntax.
|
||||
</para>
|
||||
|
||||
|
||||
<sect2 id="sect-stdio-streams">
|
||||
<title>The Standard I/O Streams</title>
|
||||
|
||||
|
|
@ -1452,12 +1432,12 @@ echo "$CUSTOMER_NAME" # Output is: Mr. Fred Smith
|
|||
process produces output) or from the terminal to the process (this is
|
||||
how the process reads input from the keyboard).
|
||||
</para>
|
||||
|
||||
|
||||
<para>
|
||||
When a process first starts, there are always three <firstterm>standard I/O
|
||||
streams</firstterm> connected to the process:
|
||||
</para>
|
||||
|
||||
|
||||
<itemizedlist>
|
||||
<listitem><para>Standard input (stdin)</para></listitem>
|
||||
<listitem><para>Standard output (stdout)</para></listitem>
|
||||
|
|
@ -1498,7 +1478,7 @@ echo "$CUSTOMER_NAME" # Output is: Mr. Fred Smith
|
|||
<blockquote>
|
||||
<example id="ex-redirect-stdout">
|
||||
<title>Redirecting Standard Output</title>
|
||||
|
||||
|
||||
<programlisting>
|
||||
#!/bin/bash
|
||||
echo Hello world > xyz
|
||||
|
|
@ -1518,10 +1498,10 @@ echo Hello world > xyz
|
|||
world</command></computeroutput>" command is redirected to the file
|
||||
<filename>xyz</filename> in the current working directory.
|
||||
</para>
|
||||
|
||||
|
||||
<warning>
|
||||
<title>Warning!</title>
|
||||
|
||||
|
||||
<para>
|
||||
If you redirect standard output to a file that already exists, the file
|
||||
is overwritten, destroying the previous contents of the file! Always be
|
||||
|
|
@ -1556,7 +1536,7 @@ echo Hello world > xyz
|
|||
<varname>$?</varname>. <xref linkend="ex-exit-status"/> shows some
|
||||
examples.
|
||||
</para>
|
||||
|
||||
|
||||
<para>
|
||||
<blockquote>
|
||||
<example id="ex-exit-status">
|
||||
|
|
@ -1565,14 +1545,14 @@ echo Hello world > xyz
|
|||
bash$ touch newfile
|
||||
bash$ echo $?
|
||||
0
|
||||
bash$ rm newfile # This command succeeds.
|
||||
bash$ rm newfile # This command succeeds.
|
||||
bash$ echo $?
|
||||
0
|
||||
bash$ rm newfile # This command fails because the file doesn't exist anymore.
|
||||
bash$ rm newfile # This command fails: the file doesn't exist anymore.
|
||||
rm: cannot remove `newfile': No such file or directory
|
||||
bash$ echo $?
|
||||
1
|
||||
bash$ echo $? # Can you explain this output?
|
||||
bash$ echo $? # Can you explain this output?
|
||||
0
|
||||
</screen>
|
||||
</example>
|
||||
|
|
|
|||
Loading…
Reference in New Issue