📄 miscellany.html
字号:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><HTML><HEAD><TITLE>Miscellany</TITLE><METANAME="GENERATOR"CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+"><LINKREL="HOME"TITLE="Advanced Bash-Scripting Guide"HREF="index.html"><LINKREL="UP"TITLE="Advanced Topics"HREF="part5.html"><LINKREL="PREVIOUS"TITLE="Scripting With Style"HREF="scrstyle.html"><LINKREL="NEXT"TITLE="Operator Precedence"HREF="opprecedence.html"><METAHTTP-EQUIV="Content-Style-Type"CONTENT="text/css"><LINKREL="stylesheet"HREF="common/kde-common.css"TYPE="text/css"><METAHTTP-EQUIV="Content-Type"CONTENT="text/html; charset=iso-8859-1"><METAHTTP-EQUIV="Content-Language"CONTENT="en"><LINKREL="stylesheet"HREF="common/kde-localised.css"TYPE="text/css"TITLE="KDE-English"><LINKREL="stylesheet"HREF="common/kde-default.css"TYPE="text/css"TITLE="KDE-Default"></HEAD><BODYCLASS="CHAPTER"BGCOLOR="#FFFFFF"TEXT="#000000"LINK="#AA0000"VLINK="#AA0055"ALINK="#AA0000"STYLE="font-family: sans-serif;"><DIVCLASS="NAVHEADER"><TABLESUMMARY="Header navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><THCOLSPAN="3"ALIGN="center">Advanced Bash-Scripting Guide: An in-depth exploration of the art of shell scripting</TH></TR><TR><TDWIDTH="10%"ALIGN="left"VALIGN="bottom"><AHREF="scrstyle.html"ACCESSKEY="P">Prev</A></TD><TDWIDTH="80%"ALIGN="center"VALIGN="bottom"></TD><TDWIDTH="10%"ALIGN="right"VALIGN="bottom"><AHREF="opprecedence.html"ACCESSKEY="N">Next</A></TD></TR></TABLE><HRALIGN="LEFT"WIDTH="100%"></DIV><DIVCLASS="CHAPTER"><H1><ANAME="MISCELLANY"></A>Chapter 33. Miscellany</H1><TABLEBORDER="0"WIDTH="100%"CELLSPACING="0"CELLPADDING="0"CLASS="EPIGRAPH"><TR><TDWIDTH="45%"> </TD><TDWIDTH="45%"ALIGN="LEFT"VALIGN="TOP"><I><P><I>Nobody really knows what the Bourne shell's grammar is. Even examination of the source code is little help.</I></P><P><I>--Tom Duff</I></P></I></TD></TR></TABLE><DIVCLASS="SECT1"><H1CLASS="SECT1"><ANAME="INTANDNONINT"></A>33.1. Interactive and non-interactive shells and scripts</H1><P>An <ICLASS="FIRSTTERM">interactive</I> shell reads commands from user input on a <TTCLASS="FILENAME">tty</TT>. Among other things, such a shell reads startup files on activation, displays a prompt, and enables job control by default. The user can <ICLASS="FIRSTTERM">interact</I> with the shell.</P><P>A shell running a script is always a non-interactive shell. All the same, the script can still access its <TTCLASS="FILENAME">tty</TT>. It is even possible to emulate an interactive shell in a script. <TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="100%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 #!/bin/bash 2 MY_PROMPT='$ ' 3 while : 4 do 5 echo -n "$MY_PROMPT" 6 read line 7 eval "$line" 8 done 9 10 exit 0 11 12 # This example script, and much of the above explanation supplied by 13 # St閜hane Chazelas (thanks again).</PRE></TD></TR></TABLE></P><P>Let us consider an <ICLASS="FIRSTTERM">interactive</I> script to be one that requires input from the user, usually with <AHREF="internal.html#READREF">read</A> statements (see <AHREF="internal.html#EX36">Example 14-3</A>). <SPANCLASS="QUOTE">"Real life"</SPAN> is actually a bit messier than that. For now, assume an interactive script is bound to a tty, a script that a user has invoked from the console or an <ICLASS="FIRSTTERM">xterm</I>.</P><P>Init and startup scripts are necessarily non-interactive, since they must run without human intervention. Many administrative and system maintenance scripts are likewise non-interactive. Unvarying repetitive tasks cry out for automation by non-interactive scripts.</P><P>Non-interactive scripts can run in the background, but interactive ones hang, waiting for input that never comes. Handle that difficulty by having an <BCLASS="COMMAND">expect</B> script or embedded <AHREF="here-docs.html#HEREDOCREF">here document</A> feed input to an interactive script running as a background job. In the simplest case, redirect a file to supply input to a <BCLASS="COMMAND">read</B> statement (<BCLASS="COMMAND">read variable <file</B>). These particular workarounds make possible general purpose scripts that run in either interactive or non-interactive modes.</P><P>If a script needs to test whether it is running in an interactive shell, it is simply a matter of finding whether the <ICLASS="FIRSTTERM">prompt</I> variable, <AHREF="variables2.html#PS1REF">$PS1</A> is set. (If the user is being prompted for input, then the script needs to display a prompt.) <TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="100%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 if [ -z $PS1 ] # no prompt? 2 then 3 # non-interactive 4 ... 5 else 6 # interactive 7 ... 8 fi</PRE></TD></TR></TABLE> <ANAME="IITEST"></A>Alternatively, the script can test for the presence of option <SPANCLASS="QUOTE">"i"</SPAN> in the <AHREF="variables2.html#FLPREF">$-</A> flag. <TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="100%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 case $- in 2 *i*) # interactive shell 3 ;; 4 *) # non-interactive shell 5 ;; 6 # (Courtesy of "UNIX F.A.Q.," 1993)</PRE></TD></TR></TABLE></P><DIVCLASS="NOTE"><TABLECLASS="NOTE"WIDTH="100%"BORDER="0"><TR><TDWIDTH="25"ALIGN="CENTER"VALIGN="TOP"><IMGSRC="common/note.png"HSPACE="5"ALT="Note"></TD><TDALIGN="LEFT"VALIGN="TOP"><P>Scripts may be forced to run in interactive mode with the <SPANCLASS="TOKEN">-i</SPAN> option or with a <TTCLASS="USERINPUT"><B>#!/bin/bash -i</B></TT> header. Be aware that this can cause erratic script behavior or show error messages even when no error is present.</P></TD></TR></TABLE></DIV></DIV></DIV><DIVCLASS="NAVFOOTER"><HRALIGN="LEFT"WIDTH="100%"><TABLESUMMARY="Footer navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top"><AHREF="scrstyle.html"ACCESSKEY="P">Prev</A></TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="index.html"ACCESSKEY="H">Home</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top"><AHREF="opprecedence.html"ACCESSKEY="N">Next</A></TD></TR><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top">Scripting With Style</TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="part5.html"ACCESSKEY="U">Up</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top">Operator Precedence</TD></TR></TABLE></DIV></BODY></HTML>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -