503 lines
7.1 KiB
HTML
503 lines
7.1 KiB
HTML
<HTML
|
|
><HEAD
|
|
><TITLE
|
|
>Usage</TITLE
|
|
><META
|
|
NAME="GENERATOR"
|
|
CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
|
|
REL="HOME"
|
|
TITLE="GNU/Linux Command-Line Tools Summary"
|
|
HREF="book1.htm"><LINK
|
|
REL="UP"
|
|
TITLE="Directing Input/Output"
|
|
HREF="c2269.htm"><LINK
|
|
REL="PREVIOUS"
|
|
TITLE="Directing Input/Output"
|
|
HREF="c2269.htm"><LINK
|
|
REL="NEXT"
|
|
TITLE="Command Substitution"
|
|
HREF="x2563.htm"></HEAD
|
|
><BODY
|
|
CLASS="SECT1"
|
|
BGCOLOR="#FFFFFF"
|
|
TEXT="#000000"
|
|
LINK="#0000FF"
|
|
VLINK="#840084"
|
|
ALINK="#0000FF"
|
|
><DIV
|
|
CLASS="NAVHEADER"
|
|
><TABLE
|
|
SUMMARY="Header navigation table"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TH
|
|
COLSPAN="3"
|
|
ALIGN="center"
|
|
>GNU/Linux Command-Line Tools Summary</TH
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="10%"
|
|
ALIGN="left"
|
|
VALIGN="bottom"
|
|
><A
|
|
HREF="c2269.htm"
|
|
ACCESSKEY="P"
|
|
>Prev</A
|
|
></TD
|
|
><TD
|
|
WIDTH="80%"
|
|
ALIGN="center"
|
|
VALIGN="bottom"
|
|
>Chapter 6. Directing Input/Output</TD
|
|
><TD
|
|
WIDTH="10%"
|
|
ALIGN="right"
|
|
VALIGN="bottom"
|
|
><A
|
|
HREF="x2563.htm"
|
|
ACCESSKEY="N"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"></DIV
|
|
><DIV
|
|
CLASS="SECT1"
|
|
><H1
|
|
CLASS="SECT1"
|
|
><A
|
|
NAME="USAGE-INPUT-OUTPUT"
|
|
></A
|
|
>Usage</H1
|
|
><P
|
|
></P
|
|
><DIV
|
|
CLASS="VARIABLELIST"
|
|
><DL
|
|
><DT
|
|
>></DT
|
|
><DD
|
|
><P
|
|
><A
|
|
NAME="AEN2368"
|
|
></A
|
|
>The greater <A
|
|
NAME="AEN2370"
|
|
></A
|
|
>than symbol <A
|
|
NAME="AEN2372"
|
|
></A
|
|
>is used to send <A
|
|
NAME="AEN2374"
|
|
></A
|
|
>information somewhere (for example a text file)</P
|
|
><P
|
|
>Example:</P
|
|
><PRE
|
|
CLASS="SCREEN"
|
|
>cat file1 file2 > file1_and_2.txt</PRE
|
|
><P
|
|
>This will concatenate <A
|
|
NAME="AEN2379"
|
|
></A
|
|
>the files together into one big file named “file1_and_2.txt”. Note that this will overwrite <A
|
|
NAME="AEN2381"
|
|
></A
|
|
>any existing <A
|
|
NAME="AEN2383"
|
|
></A
|
|
>file.</P
|
|
></DD
|
|
><DT
|
|
><</DT
|
|
><DD
|
|
><P
|
|
><A
|
|
NAME="AEN2389"
|
|
></A
|
|
>The less <A
|
|
NAME="AEN2391"
|
|
></A
|
|
>than symbol will insert <A
|
|
NAME="AEN2393"
|
|
></A
|
|
>information from somewhere (a text file) as if you typed it yourself. Often used with commands that are designed <A
|
|
NAME="AEN2395"
|
|
></A
|
|
>to get information from standard input <A
|
|
NAME="AEN2397"
|
|
></A
|
|
>only.</P
|
|
><P
|
|
>For example (using tr):</P
|
|
><PRE
|
|
CLASS="SCREEN"
|
|
>tr '[A-Z]' '[a-z]' < fileName.txt > fileNameNew.txt</PRE
|
|
><P
|
|
>The example above would insert <A
|
|
NAME="AEN2402"
|
|
></A
|
|
>the contents <A
|
|
NAME="AEN2404"
|
|
></A
|
|
>of “fileName.txt” into the input <A
|
|
NAME="AEN2406"
|
|
></A
|
|
>of <SPAN
|
|
CLASS="emphasis"
|
|
><I
|
|
CLASS="EMPHASIS"
|
|
>tr</I
|
|
></SPAN
|
|
> <A
|
|
NAME="AEN2409"
|
|
></A
|
|
>and output the results <A
|
|
NAME="AEN2411"
|
|
></A
|
|
>to “fileNameNew.txt”.</P
|
|
></DD
|
|
><DT
|
|
>>></DT
|
|
><DD
|
|
><P
|
|
><A
|
|
NAME="AEN2417"
|
|
></A
|
|
>The >> symbol <A
|
|
NAME="AEN2419"
|
|
></A
|
|
>appends (adds) information to the end of a file or creates one if the file doesn't exist.<A
|
|
NAME="AEN2421"
|
|
></A
|
|
></P
|
|
></DD
|
|
><DT
|
|
><<</DT
|
|
><DD
|
|
><P
|
|
><A
|
|
NAME="AEN2427"
|
|
></A
|
|
>The << symbol <A
|
|
NAME="AEN2429"
|
|
></A
|
|
>is sometimes used with commands that use standard input<A
|
|
NAME="AEN2431"
|
|
></A
|
|
> to take information. You simply type <SPAN
|
|
CLASS="emphasis"
|
|
><I
|
|
CLASS="EMPHASIS"
|
|
><< word</I
|
|
></SPAN
|
|
> (where word can be any string) at the end <A
|
|
NAME="AEN2434"
|
|
></A
|
|
>of the command. However its main use is in shell scripting.<A
|
|
NAME="AEN2436"
|
|
></A
|
|
> </P
|
|
><P
|
|
>The command takes your input until you type “word”, which causes the command to terminate <A
|
|
NAME="AEN2439"
|
|
></A
|
|
>and process <A
|
|
NAME="AEN2441"
|
|
></A
|
|
>the input. </P
|
|
><P
|
|
>Using << is similar to using
|
|
<B
|
|
CLASS="KEYCAP"
|
|
>CTRL</B
|
|
>-<B
|
|
CLASS="KEYCAP"
|
|
>D</B
|
|
>
|
|
<A
|
|
NAME="AEN2447"
|
|
></A
|
|
>
|
|
(EOF key)<SPAN
|
|
CLASS="emphasis"
|
|
><I
|
|
CLASS="EMPHASIS"
|
|
>, </I
|
|
></SPAN
|
|
>except it uses a string <A
|
|
NAME="AEN2450"
|
|
></A
|
|
>to perform <A
|
|
NAME="AEN2452"
|
|
></A
|
|
>the end-of-file function. This design allows it to be used in shell scripts.<A
|
|
NAME="AEN2454"
|
|
></A
|
|
></P
|
|
><P
|
|
>For example type "cat"<A
|
|
NAME="AEN2457"
|
|
></A
|
|
> (with no options...) and it will work on standard input.<A
|
|
NAME="AEN2459"
|
|
></A
|
|
></P
|
|
><P
|
|
>To stop <A
|
|
NAME="AEN2462"
|
|
></A
|
|
>entering standard input <A
|
|
NAME="AEN2464"
|
|
></A
|
|
>you would normally hit
|
|
<B
|
|
CLASS="KEYCAP"
|
|
>CTRL</B
|
|
>-<B
|
|
CLASS="KEYCAP"
|
|
>D</B
|
|
>
|
|
<A
|
|
NAME="AEN2469"
|
|
></A
|
|
>
|
|
.</P
|
|
><P
|
|
>As an alternative <A
|
|
NAME="AEN2472"
|
|
></A
|
|
>you can type "cat << FINISHED", then type what you want. </P
|
|
><P
|
|
>When you are finished,<A
|
|
NAME="AEN2475"
|
|
></A
|
|
> instead of hitting <A
|
|
NAME="AEN2477"
|
|
></A
|
|
>
|
|
<B
|
|
CLASS="KEYCAP"
|
|
>CTRL</B
|
|
>-<B
|
|
CLASS="KEYCAP"
|
|
>D</B
|
|
>
|
|
<A
|
|
NAME="AEN2482"
|
|
></A
|
|
>
|
|
you could type "FINISHED"<A
|
|
NAME="AEN2484"
|
|
></A
|
|
> and it will end (the word FINISHED will not be recorded).</P
|
|
><P
|
|
></P
|
|
></DD
|
|
><DT
|
|
>2></DT
|
|
><DD
|
|
><P
|
|
><A
|
|
NAME="AEN2491"
|
|
></A
|
|
>Redirects error output.<A
|
|
NAME="AEN2493"
|
|
></A
|
|
> For example, to redirect <A
|
|
NAME="AEN2495"
|
|
></A
|
|
>the error output <A
|
|
NAME="AEN2497"
|
|
></A
|
|
>to /dev/null<A
|
|
NAME="AEN2499"
|
|
></A
|
|
>, so you do not see it, simply append this to the end of another command...</P
|
|
><P
|
|
>For example:</P
|
|
><PRE
|
|
CLASS="SCREEN"
|
|
>make some_file 2> /dev/null</PRE
|
|
><P
|
|
>This will run make on a file and send <A
|
|
NAME="AEN2504"
|
|
></A
|
|
>all error output to /dev/null</P
|
|
></DD
|
|
><DT
|
|
>|</DT
|
|
><DD
|
|
><P
|
|
><A
|
|
NAME="AEN2510"
|
|
></A
|
|
><A
|
|
NAME="AEN2512"
|
|
></A
|
|
>The “pipe” command allows the output of one command to be sent to the input of another.</P
|
|
><P
|
|
>For example:</P
|
|
><PRE
|
|
CLASS="SCREEN"
|
|
>cat file1.txt file2.txt | less</PRE
|
|
><P
|
|
>Concatenates <A
|
|
NAME="AEN2517"
|
|
></A
|
|
>the files together, then runs <SPAN
|
|
CLASS="emphasis"
|
|
><I
|
|
CLASS="EMPHASIS"
|
|
>less</I
|
|
></SPAN
|
|
> on them. If you are only going to look <A
|
|
NAME="AEN2520"
|
|
></A
|
|
>at a single file, you would simply use <SPAN
|
|
CLASS="emphasis"
|
|
><I
|
|
CLASS="EMPHASIS"
|
|
>less<A
|
|
NAME="AEN2523"
|
|
></A
|
|
></I
|
|
></SPAN
|
|
> on the file...</P
|
|
></DD
|
|
><DT
|
|
>tee</DT
|
|
><DD
|
|
><P
|
|
><A
|
|
NAME="AEN2529"
|
|
></A
|
|
>Sends output of a program to a file and to standard output.<A
|
|
NAME="AEN2531"
|
|
></A
|
|
> Think of it as a T intersection...it goes two ways.</P
|
|
><P
|
|
>For example:</P
|
|
><PRE
|
|
CLASS="SCREEN"
|
|
>ls /home/user | tee my_directories.txt</PRE
|
|
><P
|
|
>Lists <A
|
|
NAME="AEN2536"
|
|
></A
|
|
>the files (displays the output on the screen) and sends <A
|
|
NAME="AEN2538"
|
|
></A
|
|
>the output to a file: “my_directories.txt”.</P
|
|
></DD
|
|
><DT
|
|
>&></DT
|
|
><DD
|
|
><P
|
|
><A
|
|
NAME="AEN2544"
|
|
></A
|
|
>Redirects standard output <A
|
|
NAME="AEN2546"
|
|
></A
|
|
>and error output <A
|
|
NAME="AEN2548"
|
|
></A
|
|
>to a specific <A
|
|
NAME="AEN2550"
|
|
></A
|
|
>location.<A
|
|
NAME="AEN2552"
|
|
></A
|
|
></P
|
|
><P
|
|
>For example:</P
|
|
><PRE
|
|
CLASS="SCREEN"
|
|
>make &> /dev/null</PRE
|
|
><P
|
|
>Sends <A
|
|
NAME="AEN2557"
|
|
></A
|
|
>both error output <A
|
|
NAME="AEN2559"
|
|
></A
|
|
>and standard output <A
|
|
NAME="AEN2561"
|
|
></A
|
|
>to /dev/null so you won't see anything...</P
|
|
></DD
|
|
></DL
|
|
></DIV
|
|
></DIV
|
|
><DIV
|
|
CLASS="NAVFOOTER"
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"><TABLE
|
|
SUMMARY="Footer navigation table"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="c2269.htm"
|
|
ACCESSKEY="P"
|
|
>Prev</A
|
|
></TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="book1.htm"
|
|
ACCESSKEY="H"
|
|
>Home</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="x2563.htm"
|
|
ACCESSKEY="N"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
>Directing Input/Output</TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="c2269.htm"
|
|
ACCESSKEY="U"
|
|
>Up</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
>Command Substitution</TD
|
|
></TR
|
|
></TABLE
|
|
></DIV
|
|
></BODY
|
|
></HTML
|
|
> |