301 lines
4.3 KiB
HTML
301 lines
4.3 KiB
HTML
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<!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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>Command Substitution</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="GNU/Linux Command-Line Tools Summary"
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HREF="index.html"><LINK
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REL="UP"
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TITLE="Directing Input/Output"
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HREF="directing-input-ouput.html"><LINK
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REL="PREVIOUS"
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TITLE="Usage"
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HREF="usage-input-output.html"><LINK
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REL="NEXT"
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TITLE="Performing more than one command"
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HREF="performing-more-than-one-command.html"></HEAD
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><BODY
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CLASS="SECT1"
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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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ALINK="#0000FF"
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><DIV
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CLASS="NAVHEADER"
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><TABLE
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SUMMARY="Header navigation table"
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WIDTH="100%"
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BORDER="0"
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CELLPADDING="0"
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CELLSPACING="0"
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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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>GNU/Linux Command-Line Tools Summary</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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><A
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HREF="usage-input-output.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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>Chapter 6. Directing Input/Output</TD
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><TD
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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="performing-more-than-one-command.html"
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ACCESSKEY="N"
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>Next</A
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></TD
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></TR
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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="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="COMMAND-SUBSTITUTION"
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></A
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>6.3. Command Substitution</H1
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><P
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>Command substitution is basically another way to do a pipe, you can use pipes and command substitution interchangeably, it's up to you which one you find easier...</P
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><P
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>Command substitution can be done in two distinct ways.</P
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><P
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></P
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><DIV
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CLASS="VARIABLELIST"
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><DL
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><DT
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></DT
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><DD
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><P
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><3E></P
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></DD
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><DT
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>Method<6F>One<6E>(back-quotes)<A
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NAME="COMMAND-SUBSTITUTION-BACK-QUOTES"
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></A
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></DT
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><DD
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><P
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><3E></P
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><P
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>Simply type:</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="90%"
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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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>command_1 `command_2 -options`</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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><P
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>This will execute “command_2” and it's output will become the input to “command_1”.</P
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><DIV
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CLASS="TIP"
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><P
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></P
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><TABLE
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CLASS="TIP"
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WIDTH="90%"
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BORDER="0"
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><TR
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><TD
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WIDTH="25"
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ALIGN="CENTER"
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VALIGN="TOP"
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><IMG
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SRC="../images/tip.gif"
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HSPACE="5"
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ALT="Tip"></TD
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><TH
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ALIGN="LEFT"
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VALIGN="CENTER"
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><B
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>Backquote key</B
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></TH
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></TR
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><TR
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><TD
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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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><P
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>The back-quote key is usually located at the same place as the tilde, above the [Tab] key.</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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></DD
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><DT
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>Method<6F>Two<77>(dollars<72>sign)<A
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NAME="COMMAND-SUBSTITUTION-DOLLARS-SIGN"
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></A
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></DT
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><DD
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><P
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><3E></P
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><P
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>Simply type:</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="90%"
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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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>command_1 $(command_2)</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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><P
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>This will execute “command_2” and it's output will become the input to “command_1”.</P
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></DD
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><DT
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>Using<6E>the<68>pipe<70>instead<A
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NAME="COMMAND-SUBSTITUTION-PIPE"
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></A
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></DT
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><DD
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><P
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><3E></P
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><P
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>You can of course use pipes to do the same thing, if you don't know what a pipe is, please see <A
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HREF="usage-input-output.html"
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>Section 6.2</A
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>. For example instead of doing:</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="90%"
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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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>less $cat file1.txt file2.txt</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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><P
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>You could do:</P
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><TABLE
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BORDER="1"
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BGCOLOR="#E0E0E0"
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WIDTH="90%"
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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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>cat file1.txt file2.txt | less</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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><P
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>And end up with exactly the same result, it's up to you which way you find easier.</P
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></DD
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></DL
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></DIV
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></DIV
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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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WIDTH="100%"
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BORDER="0"
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CELLPADDING="0"
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CELLSPACING="0"
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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="usage-input-output.html"
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ACCESSKEY="P"
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>Prev</A
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></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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><A
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HREF="index.html"
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ACCESSKEY="H"
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>Home</A
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></TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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><A
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HREF="performing-more-than-one-command.html"
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ACCESSKEY="N"
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>Next</A
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></TD
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></TR
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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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>Usage</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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><A
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HREF="directing-input-ouput.html"
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ACCESSKEY="U"
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>Up</A
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></TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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>Performing more than one command</TD
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></TR
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></TABLE
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></DIV
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></BODY
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></HTML
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>
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