258 lines
3.7 KiB
HTML
258 lines
3.7 KiB
HTML
<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="book1.htm"><LINK
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REL="UP"
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TITLE="Directing Input/Output"
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HREF="c2269.htm"><LINK
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REL="PREVIOUS"
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TITLE="Usage"
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HREF="x2361.htm"><LINK
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REL="NEXT"
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TITLE="Performing more than one command"
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HREF="x2622.htm"></HEAD
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>GNU/Linux Command-Line Tools Summary</TH
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>Prev</A
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><TD
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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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VALIGN="bottom"
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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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>Command Substitution</H1
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><P
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>Command substitution<A
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NAME="AEN2566"
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></A
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> is basically another way to do a pipe,<A
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NAME="AEN2568"
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></A
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> you can use pipes and command substitution interchangeably,<A
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NAME="AEN2570"
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></A
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> 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 <A
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NAME="AEN2573"
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></A
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>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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> </P
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></DD
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><DT
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>Method One (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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> </P
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><P
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>Simply type:</P
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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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><P
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>This will execute <A
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NAME="AEN2588"
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></A
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>“command_2” and it's output <A
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NAME="AEN2590"
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></A
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>will become the input to “command_1”.</P
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><DIV
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CLASS="TIP"
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><BLOCKQUOTE
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CLASS="TIP"
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><P
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><B
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>Backquote key: </B
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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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></BLOCKQUOTE
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></DIV
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></DD
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><DT
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>Method Two (dollars 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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> </P
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><P
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>Simply type:</P
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><PRE
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CLASS="SCREEN"
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>command_1 $(command_2)</PRE
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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 the pipe 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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> </P
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><P
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>You can of course use pipes <A
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NAME="AEN2609"
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></A
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>to do the same thing, if you don't know what a pipe <A
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NAME="AEN2611"
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></A
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>is, please see <A
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HREF="x2361.htm"
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>the Section called <I
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>Usage</I
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></A
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>. For example instead of doing:</P
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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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><P
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>You could do:</P
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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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><P
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>And end up with exactly <A
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NAME="AEN2618"
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></A
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>the same result,<A
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NAME="AEN2620"
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></A
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> 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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>Prev</A
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>Home</A
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HREF="x2622.htm"
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>Next</A
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></TD
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><TR
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>Usage</TD
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><TD
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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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