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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 18] 18.5 Creating and Removing Links </TITLE><METANAME="DC.title"CONTENT="UNIX Power Tools"><METANAME="DC.creator"CONTENT="Jerry Peek, Tim O'Reilly & Mike Loukides"><METANAME="DC.publisher"CONTENT="O'Reilly & Associates, Inc."><METANAME="DC.date"CONTENT="1998-08-04T21:39:00Z"><METANAME="DC.type"CONTENT="Text.Monograph"><METANAME="DC.format"CONTENT="text/html"SCHEME="MIME"><METANAME="DC.source"CONTENT="1-56592-260-3"SCHEME="ISBN"><METANAME="DC.language"CONTENT="en-US"><METANAME="generator"CONTENT="Jade 1.1/O'Reilly DocBook 3.0 to HTML 4.0"><LINKREV="made"HREF="mailto:online-books@oreilly.com"TITLE="Online Books Comments"><LINKREL="up"HREF="ch18_01.htm"TITLE="18. Linking, Renaming, and Copying Files"><LINKREL="prev"HREF="ch18_04.htm"TITLE="18.4 More About Links "><LINKREL="next"HREF="ch18_06.htm"TITLE="18.6 Stale Symbolic Links "></HEAD><BODYBGCOLOR="#FFFFFF"TEXT="#000000"><DIVCLASS="htmlnav"><H1><IMGSRC="gifs/smbanner.gif"ALT="UNIX Power Tools"USEMAP="#srchmap"BORDER="0"></H1><MAPNAME="srchmap"><AREASHAPE="RECT"COORDS="0,0,466,58"HREF="index.htm"ALT="UNIX Power Tools"><AREASHAPE="RECT"COORDS="467,0,514,18"HREF="jobjects/fsearch.htm"ALT="Search this book"></MAP><TABLEWIDTH="515"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch18_04.htm"TITLE="18.4 More About Links "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 18.4 More About Links "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 18<BR>Linking, Renaming, and Copying Files</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch18_06.htm"TITLE="18.6 Stale Symbolic Links "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 18.6 Stale Symbolic Links "BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-7945">18.5 Creating and Removing Links </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-20373"></A><ACLASS="indexterm"NAME="AUTOID-20375"></A><ACLASS="indexterm"NAME="AUTOID-20378"></A>The <EMCLASS="emphasis">ln</EM> command creates both<SPANCLASS="link">hard and soft (symbolic) links (<ACLASS="linkend"HREF="ch18_04.htm"TITLE="More About Links ">18.4</A>)</SPAN>.Only UNIX versions with symbolic links have the <EMCLASS="emphasis">-s</EM> option, though:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>ln</B></CODE> <CODECLASS="replaceable"><I>filename linkname</I></CODE> <EMCLASS="emphasis">To create a hard link</EM>% <CODECLASS="userinput"><B>ln -s</B></CODE> <CODECLASS="replaceable"><I>filename linkname</I></CODE> <EMCLASS="emphasis">To create a symbolic link</EM></PRE></BLOCKQUOTE></P><PCLASS="para">In either case, <CODECLASS="replaceable"><I>filename</I></CODE> must already exist. Otherwise youwill get an error message.If you are using Berkeley UNIX, <CODECLASS="replaceable"><I>linkname</I></CODE> must not exist - if it does, you will get an error.Under System V, <CODECLASS="replaceable"><I>linkname</I></CODE> may already exist; if you areallowed to write the file, <EMCLASS="emphasis">ln</EM> destroys its old contents andcreates your link.If you don't have write access for <CODECLASS="replaceable"><I>linkname</I></CODE>, <EMCLASS="emphasis">ln</EM> asks whether or not it is OK to override thefile's protection.For example:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>ln foo bar</B></CODE>ln: override protection 444 for bar? <CODECLASS="userinput"><B>y</B></CODE></PRE></BLOCKQUOTE></P><PCLASS="para">Typing <CODECLASS="literal">y</CODE> gives <EMCLASS="emphasis">ln</EM> permission to destroy the file <EMCLASS="emphasis">bar</EM> and createthe link.Note that this will still fail if you don't have writeaccess to the directory.</P><PCLASS="para">You are allowed to omit the <CODECLASS="replaceable"><I>linkname</I></CODE> argument from the <EMCLASS="emphasis">ln</EM>command.In this case, <EMCLASS="emphasis">ln</EM> takes the last component of <CODECLASS="replaceable"><I>filename</I></CODE> (i.e., everything after the last slash) and uses it for <CODECLASS="replaceable"><I>linkname</I></CODE>.Of course, this assumes that <CODECLASS="replaceable"><I>filename</I></CODE> doesn'trefer to the current directory.If it does, the command will fail:the link will already exist.For example, the commands below are the same:</P><PCLASS="para"><TABLECLASS="screen.co"BORDER="1"><TR><THVALIGN="TOP"><PRECLASS="calloutlist"><ACLASS="co"HREF="ch01_21.htm"TITLE="1.21 Making Pathnames ">&..</A> </PRE></TH><TDVALIGN="TOP"><PRECLASS="screen">% <CODECLASS="userinput"><B>ln -s ../archive/file.c</B></CODE>% <CODECLASS="userinput"><B>ln -s ../archive/file.c file.c</B></CODE></PRE></TD></TR></TABLE></P><PCLASS="para">Both create a link from <EMCLASS="emphasis">file.c</EM> in the current directory to<EMCLASS="emphasis">../archive/file.c</EM>.</P><PCLASS="para"><EMCLASS="emphasis">ln</EM> also lets you create a group of links with one command,provided that all of the links are in the same directory.Here's how:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>ln</B></CODE> <CODECLASS="replaceable"><I>file1 file2 file3 ... filen directory</I></CODE></PRE></BLOCKQUOTE></P><PCLASS="para">This command uses the filename from each pathname(after the last slash) as each link's name. Itthen creates all the links within the given <CODECLASS="replaceable"><I>directory</I></CODE>.For example, the first command below is equivalent to the next two:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>ln ../s/f1 ../s/f2 current</B></CODE>% <CODECLASS="userinput"><B>ln ../s/f1 current/f1</B></CODE>% <CODECLASS="userinput"><B>ln ../s/f2 current/f2</B></CODE></PRE></BLOCKQUOTE></P><PCLASS="para">You can replace this list of files with a<SPANCLASS="link">wildcard expression (<ACLASS="linkend"HREF="ch15_02.htm"TITLE="Filename Wildcards in a Nutshell ">15.2</A>)</SPAN>,as in:</P><PCLASS="para"><TABLECLASS="screen.co"BORDER="1"><TR><THVALIGN="TOP"><PRECLASS="calloutlist"><ACLASS="co"HREF="ch01_21.htm"TITLE="1.21 Making Pathnames ">&.</A> </PRE></TH><TDVALIGN="TOP"><PRECLASS="screen">% <CODECLASS="userinput"><B>ln -s ../newversion/*.[ch] </B></CODE></PRE></TD></TR></TABLE></P><PCLASS="para"><ACLASS="indexterm"NAME="UPT-ART-7945-IX-STALE-SYMBOLIC-LINKS"></A><ACLASS="indexterm"NAME="UPT-ART-7945-IX-SYMBOLIC-LINKS-STALE"></A>Note that symbolic links can<SPANCLASS="link">get out-of-date (<ACLASS="linkend"HREF="ch18_06.htm"TITLE="Stale Symbolic Links ">18.6</A>)</SPAN>.[Hard links can also be "broken" in some situations.For example, a text editor might rename the link <EMCLASS="emphasis">textfile</EM> to<EMCLASS="emphasis">textfile.bak</EM>, then create a new <EMCLASS="emphasis">textfile</EM> during editing.Previous links to <EMCLASS="emphasis">textfile</EM> will now give you <EMCLASS="emphasis">textfile.bak</EM>.To track down this problem,<SPANCLASS="link">find the links (<ACLASS="linkend"HREF="ch17_22.htm"TITLE="Finding the Links to a File ">17.22</A>)</SPAN>to each file.-<EMCLASS="emphasis">JP</EM> ]</P><PCLASS="para">To remove a link, either hard or symbolic, use the <EMCLASS="emphasis">rm</EM> command.<ACLASS="indexterm"NAME="AUTOID-20457"></A></P><DIVCLASS="sect1info"><PCLASS="SECT1INFO">- <SPANCLASS="authorinitials">ML</SPAN></P></DIV></DIV><DIVCLASS="htmlnav"><P></P><HRALIGN="LEFT"WIDTH="515"TITLE="footer"><TABLEWIDTH="515"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch18_04.htm"TITLE="18.4 More About Links "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 18.4 More About Links "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><ACLASS="book"HREF="index.htm"TITLE="UNIX Power Tools"><IMGSRC="gifs/txthome.gif"SRC="gifs/txthome.gif"ALT="UNIX Power Tools"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch18_06.htm"TITLE="18.6 Stale Symbolic Links "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 18.6 Stale Symbolic Links "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">18.4 More About Links </TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><ACLASS="index"HREF="index/idx_0.htm"TITLE="Book Index"><IMGSRC="gifs/index.gif"SRC="gifs/index.gif"ALT="Book Index"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172">18.6 Stale Symbolic Links </TD></TR></TABLE><HRALIGN="LEFT"WIDTH="515"TITLE="footer"><IMGSRC="gifs/smnavbar.gif"SRC="gifs/smnavbar.gif"USEMAP="#map"BORDER="0"ALT="The UNIX CD Bookshelf Navigation"><MAPNAME="map"><AREASHAPE="RECT"COORDS="0,0,73,21"HREF="../index.htm"ALT="The UNIX CD Bookshelf"><AREASHAPE="RECT"COORDS="74,0,163,21"HREF="index.htm"ALT="UNIX Power Tools"><AREASHAPE="RECT"COORDS="164,0,257,21"HREF="../unixnut/index.htm"ALT="UNIX in a Nutshell"><AREASHAPE="RECT"COORDS="258,0,321,21"HREF="../vi/index.htm"ALT="Learning the vi Editor"><AREASHAPE="RECT"COORDS="322,0,378,21"HREF="../sedawk/index.htm"ALT="sed & awk"><AREASHAPE="RECT"COORDS="379,0,438,21"HREF="../ksh/index.htm"ALT="Learning the Korn Shell"><AREASHAPE="RECT"COORDS="439,0,514,21"HREF="../lrnunix/index.htm"ALT="Learning the UNIX Operating System"></MAP></DIV></BODY></HTML>⌨️ 快捷键说明
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