426 lines
5.8 KiB
HTML
426 lines
5.8 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML
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><HEAD
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><TITLE
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>Quoting</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
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REL="HOME"
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TITLE="Advanced Bash-Scripting Guide"
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HREF="index.html"><LINK
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REL="UP"
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TITLE="Basics"
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HREF="part2.html"><LINK
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REL="PREVIOUS"
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TITLE="Special Variable Types"
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HREF="othertypesv.html"><LINK
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REL="NEXT"
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TITLE="Quoting Variables"
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HREF="quotingvar.html"></HEAD
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><BODY
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CLASS="CHAPTER"
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BGCOLOR="#FFFFFF"
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TEXT="#000000"
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LINK="#0000FF"
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VLINK="#840084"
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><DIV
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SUMMARY="Header navigation table"
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>Advanced Bash-Scripting Guide: </TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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ACCESSKEY="P"
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>Prev</A
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="quotingvar.html"
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ACCESSKEY="N"
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>Next</A
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></TD
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><DIV
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CLASS="CHAPTER"
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><H1
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><A
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NAME="QUOTING"
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></A
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>Chapter 5. Quoting</H1
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><DIV
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CLASS="TOC"
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><DL
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><DT
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><B
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>Table of Contents</B
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></DT
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><DT
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>5.1. <A
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HREF="quotingvar.html"
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>Quoting Variables</A
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></DT
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><DT
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>5.2. <A
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HREF="escapingsection.html"
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>Escaping</A
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></DT
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></DL
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></DIV
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><P
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><A
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NAME="QUOTINGREF"
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></A
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></P
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><P
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>Quoting means just that, bracketing a string in quotes. This
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has the effect of protecting <A
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HREF="special-chars.html#SCHARLIST1"
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>special
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characters</A
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> in the string from reinterpretation
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or expansion by the shell or shell script. (A character
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is <SPAN
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CLASS="QUOTE"
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>"special"</SPAN
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> if it has an interpretation
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other than its literal meaning. For example, the <A
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HREF="special-chars.html#ASTERISKREF"
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>asterisk *</A
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> represents
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a <I
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CLASS="FIRSTTERM"
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>wild card</I
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> character in
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<A
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HREF="globbingref.html"
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>globbing</A
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> and <A
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HREF="regexp.html#REGEXREF"
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>Regular Expressions</A
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>).</P
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><P
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> <TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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><TT
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CLASS="PROMPT"
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>bash$ </TT
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><TT
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CLASS="USERINPUT"
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><B
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>ls -l [Vv]*</B
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></TT
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>
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<TT
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CLASS="COMPUTEROUTPUT"
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>-rw-rw-r-- 1 bozo bozo 324 Apr 2 15:05 VIEWDATA.BAT
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-rw-rw-r-- 1 bozo bozo 507 May 4 14:25 vartrace.sh
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-rw-rw-r-- 1 bozo bozo 539 Apr 14 17:11 viewdata.sh</TT
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>
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<TT
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CLASS="PROMPT"
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>bash$ </TT
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><TT
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CLASS="USERINPUT"
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><B
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>ls -l '[Vv]*'</B
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></TT
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>
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<TT
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CLASS="COMPUTEROUTPUT"
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>ls: [Vv]*: No such file or directory</TT
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></PRE
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></FONT
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></TD
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></TR
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></TABLE
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>
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</P
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><P
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><A
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NAME="QUOTINGDEF"
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></A
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></P
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><TABLE
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CLASS="SIDEBAR"
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BORDER="1"
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CELLPADDING="5"
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><TR
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><TD
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><DIV
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CLASS="SIDEBAR"
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><A
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NAME="AEN2596"
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></A
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><P
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></P
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><P
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>In everyday speech or writing, when we
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<SPAN
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CLASS="QUOTE"
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>"quote"</SPAN
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> a phrase, we set it apart and give it special
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meaning. In a Bash script, when we <I
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CLASS="FIRSTTERM"
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>quote</I
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> a
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string, we set it apart and protect its <I
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CLASS="FIRSTTERM"
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>literal</I
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>
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meaning.</P
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><P
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></P
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></DIV
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></TD
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></TR
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></TABLE
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><P
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>Certain programs and utilities reinterpret or expand
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special characters in a quoted string. An important use of
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quoting is protecting a command-line parameter from the shell,
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but still letting the calling program expand it.</P
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><P
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> <TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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><TT
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CLASS="PROMPT"
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>bash$ </TT
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><TT
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CLASS="USERINPUT"
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><B
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>grep '[Ff]irst' *.txt</B
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></TT
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>
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<TT
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CLASS="COMPUTEROUTPUT"
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>file1.txt:This is the first line of file1.txt.
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file2.txt:This is the First line of file2.txt.</TT
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></PRE
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></FONT
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></TD
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></TR
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></TABLE
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>
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</P
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><P
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>Note that the unquoted <TT
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CLASS="USERINPUT"
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><B
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>grep [Ff]irst *.txt</B
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></TT
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>
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works under the Bash shell.
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<A
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NAME="AEN2609"
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HREF="#FTN.AEN2609"
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><SPAN
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CLASS="footnote"
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>[1]</SPAN
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></A
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>
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</P
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><P
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>Quoting can also suppress <A
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HREF="internal.html#ECHOREF"
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>echo's</A
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>
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<SPAN
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CLASS="QUOTE"
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>"appetite"</SPAN
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> for newlines.</P
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><P
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> <TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><FONT
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COLOR="#000000"
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><PRE
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CLASS="SCREEN"
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><TT
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CLASS="PROMPT"
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>bash$ </TT
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><TT
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CLASS="USERINPUT"
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><B
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>echo $(ls -l)</B
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></TT
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>
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<TT
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CLASS="COMPUTEROUTPUT"
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>total 8 -rw-rw-r-- 1 bo bo 13 Aug 21 12:57 t.sh -rw-rw-r-- 1 bo bo 78 Aug 21 12:57 u.sh</TT
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>
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<TT
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CLASS="PROMPT"
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>bash$ </TT
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><TT
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CLASS="USERINPUT"
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><B
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>echo "$(ls -l)"</B
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></TT
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>
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<TT
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CLASS="COMPUTEROUTPUT"
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>total 8
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-rw-rw-r-- 1 bo bo 13 Aug 21 12:57 t.sh
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-rw-rw-r-- 1 bo bo 78 Aug 21 12:57 u.sh</TT
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></PRE
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></FONT
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></TD
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></TR
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></TABLE
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>
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</P
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></DIV
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><H3
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CLASS="FOOTNOTES"
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>Notes</H3
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><TABLE
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BORDER="0"
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CLASS="FOOTNOTES"
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WIDTH="100%"
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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WIDTH="5%"
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><A
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NAME="FTN.AEN2609"
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HREF="quoting.html#AEN2609"
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><SPAN
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CLASS="footnote"
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>[1]</SPAN
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></A
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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WIDTH="95%"
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><P
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>Unless there is a file named
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<TT
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CLASS="FILENAME"
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>first</TT
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> in the current working directory. Yet
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another reason to <I
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CLASS="FIRSTTERM"
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>quote</I
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>. (Thank you, Harald
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Koenig, for pointing this out.</P
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></TD
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></TR
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></TABLE
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><DIV
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CLASS="NAVFOOTER"
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><HR
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ALIGN="LEFT"
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WIDTH="100%"><TABLE
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SUMMARY="Footer navigation table"
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><TR
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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><A
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HREF="othertypesv.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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WIDTH="34%"
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VALIGN="top"
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>Home</A
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HREF="quotingvar.html"
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ACCESSKEY="N"
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>Next</A
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
|
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>Special Variable Types</TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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>Up</A
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VALIGN="top"
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>Quoting Variables</TD
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></TR
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></TABLE
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