filearchiv.html

Shall高级编程

><DL
><DT
><A
NAME="GZIPREF"
></A
><B
CLASS="COMMAND"
>gzip</B
></DT
><DD
><P
>The standard GNU/UNIX compression utility, replacing
	      the inferior and proprietary
	      <B
CLASS="COMMAND"
>compress</B
>. The corresponding decompression
	      command is <B
CLASS="COMMAND"
>gunzip</B
>, which is the equivalent of
	      <B
CLASS="COMMAND"
>gzip -d</B
>.</P
><DIV
CLASS="NOTE"
><TABLE
CLASS="NOTE"
WIDTH="90%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="common/note.png"
HSPACE="5"
ALT="Note"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>The <TT
CLASS="OPTION"
>-c</TT
> option sends the output of
	      <B
CLASS="COMMAND"
>gzip</B
> to <TT
CLASS="FILENAME"
>stdout</TT
>. This
	      is useful when <A
HREF="special-chars.html#PIPEREF"
>piping</A
> to other
	      commands.</P
></TD
></TR
></TABLE
></DIV
><P
><A
NAME="ZCATREF"
></A
></P
><P
>The <B
CLASS="COMMAND"
>zcat</B
> filter decompresses a
	      <I
CLASS="FIRSTTERM"
>gzipped</I
> file to
	      <TT
CLASS="FILENAME"
>stdout</TT
>, as possible input to a pipe or
	      redirection. This is, in effect, a <B
CLASS="COMMAND"
>cat</B
>
	      command that works on compressed files (including files
	      processed with the older <A
HREF="filearchiv.html#COMPRESSREF"
>compress</A
>
	      utility). The <B
CLASS="COMMAND"
>zcat</B
> command is equivalent to
	      <B
CLASS="COMMAND"
>gzip -dc</B
>.</P
><DIV
CLASS="CAUTION"
><TABLE
CLASS="CAUTION"
WIDTH="90%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="common/caution.png"
HSPACE="5"
ALT="Caution"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>On some commercial UNIX systems, <B
CLASS="COMMAND"
>zcat</B
>
	      is a synonym for <B
CLASS="COMMAND"
>uncompress -c</B
>,
	      and will not work on <I
CLASS="FIRSTTERM"
>gzipped</I
>
	      files.</P
></TD
></TR
></TABLE
></DIV
><P
>See also <A
HREF="comparison-ops.html#EX14"
>Example 7-7</A
>.</P
></DD
><DT
><A
NAME="BZIPREF"
></A
><B
CLASS="COMMAND"
>bzip2</B
></DT
><DD
><P
>An alternate compression utility, usually more efficient
	      (but slower) than <B
CLASS="COMMAND"
>gzip</B
>, especially on
	      large files. The corresponding decompression command is
	      <B
CLASS="COMMAND"
>bunzip2</B
>.</P
><DIV
CLASS="NOTE"
><TABLE
CLASS="NOTE"
WIDTH="90%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="common/note.png"
HSPACE="5"
ALT="Note"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>Newer versions of <A
HREF="filearchiv.html#TARREF"
>tar</A
> have been patched with
	      <B
CLASS="COMMAND"
>bzip2</B
> support.</P
></TD
></TR
></TABLE
></DIV
></DD
><DT
><A
NAME="COMPRESSREF"
></A
><B
CLASS="COMMAND"
>compress</B
>, <A
NAME="UNCOMPRESSREF"
></A
><B
CLASS="COMMAND"
>uncompress</B
></DT
><DD
><P
>This is an older, proprietary compression
	      utility found in commercial UNIX distributions. The
	      more efficient <B
CLASS="COMMAND"
>gzip</B
> has largely
	      replaced it. Linux distributions generally include a
	      <B
CLASS="COMMAND"
>compress</B
> workalike for compatibility,
	      although <B
CLASS="COMMAND"
>gunzip</B
> can unarchive files
	      treated with <B
CLASS="COMMAND"
>compress</B
>.</P
><DIV
CLASS="TIP"
><TABLE
CLASS="TIP"
WIDTH="90%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="common/tip.png"
HSPACE="5"
ALT="Tip"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>The <B
CLASS="COMMAND"
>znew</B
> command transforms
	      <I
CLASS="FIRSTTERM"
>compressed</I
> files into
	      <I
CLASS="FIRSTTERM"
>gzipped</I
> ones.</P
></TD
></TR
></TABLE
></DIV
></DD
><DT
><A
NAME="SQREF"
></A
><B
CLASS="COMMAND"
>sq</B
></DT
><DD
><P
>Yet another compression (<B
CLASS="COMMAND"
>sq</B
>ueeze)
	      utility, a filter that works only on sorted
	      ASCII word lists. It uses the standard invocation
	      syntax for a filter, <B
CLASS="COMMAND"
>sq &#60; input-file &#62;
	      output-file</B
>.  Fast, but not nearly as efficient
	      as <A
HREF="filearchiv.html#GZIPREF"
>gzip</A
>.  The corresponding
	      uncompression filter is <B
CLASS="COMMAND"
>unsq</B
>, invoked
	      like <B
CLASS="COMMAND"
>sq</B
>.</P
><DIV
CLASS="TIP"
><TABLE
CLASS="TIP"
WIDTH="90%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="common/tip.png"
HSPACE="5"
ALT="Tip"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>The output of <B
CLASS="COMMAND"
>sq</B
> may be
	        piped to <B
CLASS="COMMAND"
>gzip</B
> for further
		compression.</P
></TD
></TR
></TABLE
></DIV
></DD
><DT
><A
NAME="ZIPREF"
></A
><B
CLASS="COMMAND"
>zip</B
>, <B
CLASS="COMMAND"
>unzip</B
></DT
><DD
><P
>Cross-platform file archiving and compression utility
	      compatible with DOS <I
CLASS="FIRSTTERM"
>pkzip.exe</I
>.
	      <SPAN
CLASS="QUOTE"
>"Zipped"</SPAN
> archives seem to be a more
	      common medium of file exchange on the Internet than
	      <SPAN
CLASS="QUOTE"
>"tarballs."</SPAN
></P
></DD
><DT
><A
NAME="UNARCREF"
></A
><B
CLASS="COMMAND"
>unarc</B
>, <B
CLASS="COMMAND"
>unarj</B
>, <B
CLASS="COMMAND"
>unrar</B
></DT
><DD
><P
>These Linux utilities permit unpacking archives
	      compressed with the DOS <I
CLASS="FIRSTTERM"
>arc.exe</I
>,
	      <I
CLASS="FIRSTTERM"
>arj.exe</I
>, and
	      <I
CLASS="FIRSTTERM"
>rar.exe</I
> programs.</P
></DD
><DT
><A
NAME="LZMAREF"
></A
><B
CLASS="COMMAND"
>lzma</B
>, <B
CLASS="COMMAND"
>unlzma</B
>, <B
CLASS="COMMAND"
>lzcat</B
></DT
><DD
><P
>Highly efficient Lempel-Ziv-Markov compression.
	      The syntax of <I
CLASS="FIRSTTERM"
>lzma</I
> is similar to
              that of <I
CLASS="FIRSTTERM"
>gzip</I
>. The <A
HREF="http://www.7-zip.org/sdk.html"
TARGET="_top"
>7-zip Website</A
>
              has more information.</P
></DD
></DL
></DIV
><DIV
CLASS="VARIABLELIST"
><P
><B
><A
NAME="FAINFORMATION1"
></A
>File Information</B
></P
><DL
><DT
><A
NAME="FILEREF"
></A
><B
CLASS="COMMAND"
>file</B
></DT
><DD
><P
>A utility for identifying file types. The command
	      <TT
CLASS="USERINPUT"
><B
>file file-name</B
></TT
> will return a
	      file specification for <TT
CLASS="FILENAME"
>file-name</TT
>,
	      such as <TT
CLASS="COMPUTEROUTPUT"
>ascii text</TT
> or
	      <TT
CLASS="COMPUTEROUTPUT"
>data</TT
>. It references
	      the <A
HREF="sha-bang.html#MAGNUMREF"
>magic numbers</A
>
	      found in <TT
CLASS="FILENAME"
>/usr/share/magic</TT
>,
	      <TT
CLASS="FILENAME"
>/etc/magic</TT
>, or
	      <TT
CLASS="FILENAME"
>/usr/lib/magic</TT
>, depending on the
	      Linux/UNIX distribution.</P
><P
>The <TT
CLASS="OPTION"
>-f</TT
> option causes
	      <B
CLASS="COMMAND"
>file</B
> to run in <A
HREF="timedate.html#BATCHPROCREF"
>batch</A
> mode, to read from
	      a designated file a list of filenames to analyze. The
	      <TT
CLASS="OPTION"
>-z</TT
> option, when used on a compressed
	      target file, forces an attempt to analyze the uncompressed
	      file type.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>file test.tar.gz</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>test.tar.gz: gzip compressed data, deflated,
 last modified: Sun Sep 16 13:34:51 2001, os: Unix</TT
>
 
 <TT
CLASS="PROMPT"
>bash </TT
><TT
CLASS="USERINPUT"
><B
>file -z test.tar.gz</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>test.tar.gz: GNU tar archive (gzip compressed data, deflated,
 last modified: Sun Sep 16 13:34:51 2001, os: Unix)</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;# Find sh and Bash scripts in a given directory:
   2&nbsp;
   3&nbsp;DIRECTORY=/usr/local/bin
   4&nbsp;KEYWORD=Bourne
   5&nbsp;# Bourne and Bourne-Again shell scripts
   6&nbsp;
   7&nbsp;file $DIRECTORY/* | fgrep $KEYWORD
   8&nbsp;
   9&nbsp;# Output:
  10&nbsp;
  11&nbsp;# /usr/local/bin/burn-cd:          Bourne-Again shell script text executable
  12&nbsp;# /usr/local/bin/burnit:           Bourne-Again shell script text executable
  13&nbsp;# /usr/local/bin/cassette.sh:      Bourne shell script text executable
  14&nbsp;# /usr/local/bin/copy-cd:          Bourne-Again shell script text executable
  15&nbsp;# . . .</PRE
></TD
></TR
></TABLE
>
	    </P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="STRIPC"
></A
><P
><B
>Example 15-31. Stripping comments from C program files</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# strip-comment.sh: Strips out the comments (/* COMMENT */) in a C program.
   3&nbsp;
   4&nbsp;E_NOARGS=0
   5&nbsp;E_ARGERROR=66
   6&nbsp;E_WRONG_FILE_TYPE=67
   7&nbsp;
   8&nbsp;if [ $# -eq "$E_NOARGS" ]
   9&nbsp;then
  10&nbsp;  echo "Usage: `basename $0` C-program-file" &#62;&#38;2 # Error message to stderr.
  11&nbsp;  exit $E_ARGERROR
  12&nbsp;fi  
  13&nbsp;
  14&nbsp;# Test for correct file type.
  15&nbsp;type=`file $1 | awk '{ print $2, $3, $4, $5 }'`
  16&nbsp;# "file $1" echoes file type . . .
  17&nbsp;# Then awk removes the first field, the filename . . .
  18&nbsp;# Then the result is fed into the variable "type."
  19&nbsp;correct_type="ASCII C program text"
  20&nbsp;
  21&nbsp;if [ "$type" != "$correct_type" ]
  22&nbsp;then
  23&nbsp;  echo
  24&nbsp;  echo "This script works on C program files only."
  25&nbsp;  echo
  26&nbsp;  exit $E_WRONG_FILE_TYPE
  27&nbsp;fi  
  28&nbsp;
  29&nbsp;
  30&nbsp;# Rather cryptic sed script:
  31&nbsp;#--------
  32&nbsp;sed '
  33&nbsp;/^\/\*/d
  34&nbsp;/.*\*\//d
  35&nbsp;' $1
  36&nbsp;#--------
  37&nbsp;# Easy to understand if you take several hours to learn sed fundamentals.
  38&nbsp;
  39&nbsp;
  40&nbsp;#  Need to add one more line to the sed script to deal with
  41&nbsp;#+ case where line of code has a comment following it on same line.
  42&nbsp;#  This is left as a non-trivial exercise.
  43&nbsp;
  44&nbsp;#  Also, the above code deletes non-comment lines with a "*/" . . .
  45&nbsp;#+ not a desirable result.
  46&nbsp;
  47&nbsp;exit 0
  48&nbsp;
  49&nbsp;
  50&nbsp;# ----------------------------------------------------------------
  51&nbsp;# Code below this line will not execute because of 'exit 0' above.
  52&nbsp;
  53&nbsp;# Stephane Chazelas suggests the following alternative:
  54&nbsp;
  55&nbsp;usage() {
  56&nbsp;  echo "Usage: `basename $0` C-program-file" &#62;&#38;2
  57&nbsp;  exit 1
  58&nbsp;}
  59&nbsp;
  60&nbsp;WEIRD=`echo -n -e '\377'`   # or WEIRD=$'\377'
  61&nbsp;[[ $# -eq 1 ]] || usage
  62&nbsp;case `file "$1"` in
  63&nbsp;  *"C program text"*) sed -e "s%/\*%${WEIRD}%g;s%\*/%${WEIRD}%g" "$1" \
  64&nbsp;     | tr '\377\n' '\n\377' \
  65&nbsp;     | sed -ne 'p;n' \
  66&nbsp;     | tr -d '\n' | tr '\377' '\n';;
  67&nbsp;  *) usage;;
  68&nbsp;esac
  69&nbsp;
  70&nbsp;#  This is still fooled by things like:
  71&nbsp;#  printf("/*");
  72&nbsp;#  or
  73&nbsp;#  /*  /* buggy embedded comment */
  74&nbsp;#
  75&nbsp;#  To handle all special cases (comments in strings, comments in string
  76&nbsp;#+ where there is a \", \\" ...),
  77&nbsp;#+ the only way is to write a C parser (using lex or yacc perhaps?).
  78&nbsp;
  79&nbsp;exit 0</PRE
></TD
></TR
></TABLE
><HR></DIV
></DD
><DT
><A
NAME="WHICHREF"
></A
><B
CLASS="COMMAND"
>which</B
></DT
><DD
><P
><B
CLASS="COMMAND"
>which command</B
> gives the full path
	      to <SPAN
CLASS="QUOTE"
>"command."</SPAN
> This is useful for finding
	      out whether a particular command or utility is installed
	      on the system.</P
><P
><TT
CLASS="USERINPUT"
><B
>$bash which rm</B
></TT
>
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="COMPUTEROUTPUT"
>/usr/bin/rm</TT
></PRE
></TD
></TR
></TABLE
>
	  </P
><P
>For an interesting use of this command, see <A
HREF="colorizing.html#HORSERACE"
>Example 33-14</A
>.</P
></DD
><DT
><A
NAME="WHEREISREF"
></A
><B
CLASS="COMMAND"
>whereis</B
></DT
><DD
><P
>Similar to <B
CLASS="COMMAND"
>which</B
>, above,
	      <B
CLASS="COMMAND"
>whereis command</B
> gives the
	      full path to <SPAN
CLASS="QUOTE"
>"command,"</SPAN
> but also to its
	      <A
HREF="external.html#MANREF"
>manpage</A
>.</P
><P
><TT
CLASS="USERINPUT"
><B
>$bash whereis rm</B
></TT
>
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="COMPUTEROUTPUT"
>rm: /bin/rm /usr/share/man/man1/rm.1.bz2</TT
></PRE
></TD
></TR
></TABLE
>
	  </P
></DD
><DT
><A
NAME="WHATISREF"
></A
><B
CLASS="COMMAND"
>whatis</B
></DT
><DD
><P
><B
CLASS="COMMAND"
>whatis command</B
> looks up
	      <SPAN
CLASS="QUOTE"