textproc.html

Shall高级编程

CLASS="PROGRAMLISTING"
>   1 grep -c txt *.sgml   # (number of occurrences of "txt" in "*.sgml" files)
   2 
   3 
   4 #   grep -cz .
   5 #            ^ dot
   6 # means count (-c) zero-separated (-z) items matching "."
   7 # that is, non-empty ones (containing at least 1 character).
   8 # 
   9 printf 'a b\nc  d\n\n\n\n\n\000\n\000e\000\000\nf' | grep -cz .     # 3
  10 printf 'a b\nc  d\n\n\n\n\n\000\n\000e\000\000\nf' | grep -cz '$'   # 5
  11 printf 'a b\nc  d\n\n\n\n\n\000\n\000e\000\000\nf' | grep -cz '^'   # 5
  12 #
  13 printf 'a b\nc  d\n\n\n\n\n\000\n\000e\000\000\nf' | grep -c '$'    # 9
  14 # By default, newline chars (\n) separate items to match. 
  15 
  16 # Note that the -z option is GNU "grep" specific.
  17 
  18 
  19&nbsp;# Thanks, S.C.</PRE
></TD
></TR
></TABLE
>
            </P
><P
>The <TT
CLASS="OPTION"
>--color</TT
> (or <TT
CLASS="OPTION"
>--colour</TT
>)
	      option marks the matching string in color (on the console
	      or in an <I
CLASS="FIRSTTERM"
>xterm</I
> window). Since
	      <I
CLASS="FIRSTTERM"
>grep</I
> prints out each entire line
	      containing the matching pattern, this lets you see exactly
	      <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>what</I
></SPAN
> is being matched. See also
	      the <TT
CLASS="OPTION"
>-o</TT
> option, which shows only the
	      matching portion of the line(s).</P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="FROMSH"
></A
><P
><B
>Example 15-16. Printing out the <I
CLASS="FIRSTTERM"
>From</I
> lines in
	        stored e-mail messages</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# from.sh
   3&nbsp;
   4&nbsp;#  Emulates the useful "from" utility in Solaris, BSD, etc.
   5&nbsp;#  Echoes the "From" header line in all messages
   6&nbsp;#+ in your e-mail directory.
   7&nbsp;
   8&nbsp;
   9&nbsp;MAILDIR=~/mail/*               #  No quoting of variable. Why?
  10&nbsp;GREP_OPTS="-H -A 5 --color"    #  Show file, plus extra context lines
  11&nbsp;                               #+ and display "From" in color.
  12&nbsp;TARGETSTR="^From"              # "From" at beginning of line.
  13&nbsp;
  14&nbsp;for file in $MAILDIR           #  No quoting of variable.
  15&nbsp;do
  16&nbsp;  grep $GREP_OPTS "$TARGETSTR" "$file"
  17&nbsp;  #    ^^^^^^^^^^              #  Again, do not quote this variable.
  18&nbsp;  echo
  19&nbsp;done
  20&nbsp;
  21&nbsp;exit $?
  22&nbsp;
  23&nbsp;#  Might wish to pipe the output of this script to 'more' or
  24&nbsp;#+ redirect it to a file . . .</PRE
></TD
></TR
></TABLE
><HR></DIV
><P
>When invoked with more than one target file given,
	      <B
CLASS="COMMAND"
>grep</B
> specifies which file contains
	      matches.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>grep Linux osinfo.txt misc.txt</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>osinfo.txt:This is a file containing information about Linux.
 osinfo.txt:The GPL governs the distribution of the Linux operating system.
 misc.txt:The Linux operating system is steadily gaining in popularity.</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </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
>To force <B
CLASS="COMMAND"
>grep</B
> to show the filename
	      when searching only one target file, simply give
	      <TT
CLASS="FILENAME"
>/dev/null</TT
> as the second file.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>grep Linux osinfo.txt /dev/null</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>osinfo.txt:This is a file containing information about Linux.
 osinfo.txt:The GPL governs the distribution of the Linux operating system.</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
></TD
></TR
></TABLE
></DIV
><P
>If there is a successful match, <B
CLASS="COMMAND"
>grep</B
>
	      returns an <A
HREF="exit-status.html#EXITSTATUSREF"
>exit status</A
>
	      of 0, which makes it useful in a condition test in a
	      script, especially in combination with the <TT
CLASS="OPTION"
>-q</TT
>
	      option to suppress output.
	        <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;SUCCESS=0                      # if grep lookup succeeds
   2&nbsp;word=Linux
   3&nbsp;filename=data.file
   4&nbsp;
   5&nbsp;grep -q "$word" "$filename"    #  The "-q" option
   6&nbsp;                               #+ causes nothing to echo to stdout.
   7&nbsp;if [ $? -eq $SUCCESS ]
   8&nbsp;# if grep -q "$word" "$filename"   can replace lines 5 - 7.
   9&nbsp;then
  10&nbsp;  echo "$word found in $filename"
  11&nbsp;else
  12&nbsp;  echo "$word not found in $filename"
  13&nbsp;fi</PRE
></TD
></TR
></TABLE
>
            </P
><P
><A
HREF="debugging.html#ONLINE"
>Example 29-6</A
> demonstrates how to use
	      <B
CLASS="COMMAND"
>grep</B
> to search for a word pattern in
	      a system logfile.</P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="GRP"
></A
><P
><B
>Example 15-17. Emulating <I
CLASS="FIRSTTERM"
>grep</I
> in a script</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# grp.sh: Very crude reimplementation of 'grep'.
   3&nbsp;
   4&nbsp;E_BADARGS=65
   5&nbsp;
   6&nbsp;if [ -z "$1" ]    # Check for argument to script.
   7&nbsp;then
   8&nbsp;  echo "Usage: `basename $0` pattern"
   9&nbsp;  exit $E_BADARGS
  10&nbsp;fi  
  11&nbsp;
  12&nbsp;echo
  13&nbsp;
  14&nbsp;for file in *     # Traverse all files in $PWD.
  15&nbsp;do
  16&nbsp;  output=$(sed -n /"$1"/p $file)  # Command substitution.
  17&nbsp;
  18&nbsp;  if [ ! -z "$output" ]           # What happens if "$output" is not quoted?
  19&nbsp;  then
  20&nbsp;    echo -n "$file: "
  21&nbsp;    echo $output
  22&nbsp;  fi              #  sed -ne "/$1/s|^|${file}: |p"  is equivalent to above.
  23&nbsp;
  24&nbsp;  echo
  25&nbsp;done  
  26&nbsp;
  27&nbsp;echo
  28&nbsp;
  29&nbsp;exit 0
  30&nbsp;
  31&nbsp;# Exercises:
  32&nbsp;# ---------
  33&nbsp;# 1) Add newlines to output, if more than one match in any given file.
  34&nbsp;# 2) Add features.</PRE
></TD
></TR
></TABLE
><HR></DIV
><P
>How can <B
CLASS="COMMAND"
>grep</B
> search for two (or
	      more) separate patterns? What if you want
	      <B
CLASS="COMMAND"
>grep</B
> to display all lines in a file
	      or files that contain both <SPAN
CLASS="QUOTE"
>"pattern1"</SPAN
>
	      <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>and</I
></SPAN
> <SPAN
CLASS="QUOTE"
>"pattern2"</SPAN
>?</P
><P
>One method is to <A
HREF="special-chars.html#PIPEREF"
>pipe</A
> the result of <B
CLASS="COMMAND"
>grep
	      pattern1</B
> to <B
CLASS="COMMAND"
>grep pattern2</B
>.</P
><P
>For example, given the following file:</P
><P
>	    <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;# Filename: tstfile
   2&nbsp;
   3&nbsp;This is a sample file.
   4&nbsp;This is an ordinary text file.
   5&nbsp;This file does not contain any unusual text.
   6&nbsp;This file is not unusual.
   7&nbsp;Here is some text.</PRE
></TD
></TR
></TABLE
>
            </P
><P
>Now, let's search this file for lines containing
	      <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>both</I
></SPAN
> <SPAN
CLASS="QUOTE"
>"file"</SPAN
> and
	      <SPAN
CLASS="QUOTE"
>"text"</SPAN
> . . . </P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>grep file tstfile</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
># Filename: tstfile
 This is a sample file.
 This is an ordinary text file.
 This file does not contain any unusual text.
 This file is not unusual.</TT
>
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>grep file tstfile | grep text</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>This is an ordinary text file.
 This file does not contain any unusual text.</TT
></PRE
></TD
></TR
></TABLE
><P
>--</P
><P
><A
NAME="EGREPREF"
></A
><B
CLASS="COMMAND"
>egrep</B
>
	      -- <I
CLASS="FIRSTTERM"
>extended grep</I
> -- is the same
	      as <B
CLASS="COMMAND"
>grep -E</B
>. This uses a somewhat
	      different, extended set of <A
HREF="regexp.html#REGEXREF"
>Regular
	      Expressions</A
>, which can make the search a bit more
	      flexible. It also allows the boolean |
	      (<I
CLASS="FIRSTTERM"
>or</I
>) operator.
	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash $ </TT
><TT
CLASS="USERINPUT"
><B
>egrep 'matches|Matches' file.txt</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>Line 1 matches.
 Line 3 Matches.
 Line 4 contains matches, but also Matches</TT
>
               </PRE
></TD
></TR
></TABLE
>
	      </P
><P
><A
NAME="FGREPREF"
></A
><B
CLASS="COMMAND"
>fgrep</B
> --
	      <I
CLASS="FIRSTTERM"
>fast grep</I
> -- is the same as
	      <B
CLASS="COMMAND"
>grep -F</B
>. It does a literal string search
	      (no <A
HREF="regexp.html#REGEXREF"
>Regular Expressions</A
>),
	      which generally speeds things up a bit.</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
>On some Linux distros, <B
CLASS="COMMAND"
>egrep</B
> and
	      <B
CLASS="COMMAND"
>fgrep</B
> are symbolic links to, or aliases for
	      <B
CLASS="COMMAND"
>grep</B
>, but invoked with the
	      <TT
CLASS="OPTION"
>-E</TT
> and <TT
CLASS="OPTION"
>-F</TT
> options,
	      respectively.</P
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="DICTLOOKUP"
></A
><P
><B
>Example 15-18. Looking up definitions in <I
CLASS="CITETITLE"
>Webster's 1913 Dictionary</I
></B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# dict-lookup.sh
   3&nbsp;
   4&nbsp;#  This script looks up definitions in the 1913 Webster's Dictionary.
   5&nbsp;#  This Public Domain dictionary is available for download
   6&nbsp;#+ from various sites, including
   7&nbsp;#+ Project Gutenberg (http://www.gutenberg.org/etext/247).
   8&nbsp;#
   9&nbsp;#  Convert it from DOS to UNIX format (only LF at end of line)
  10&nbsp;#+ before using it with this script.
  11&nbsp;#  Store the file in plain, uncompressed ASCII.
  12&nbsp;#  Set DEFAULT_DICTFILE variable below to path/filename.
  13&nbsp;
  14&nbsp;
  15&nbsp;E_BADARGS=65
  16&nbsp;MAXCONTEXTLINES=50                        # Maximum number of lines to show.
  17&nbsp;DEFAULT_DICTFILE="/usr/share/dict/webster1913-dict.txt"
  18&nbsp;                                          # Default dictionary file pathname.
  19&nbsp;                                          # Change this as necessary.
  20&nbsp;#  Note:
  21&nbsp;#  ----
  22&nbsp;#  This particular edition of the 1913 Webster's
  23&nbsp;#+ begins each entry with an uppercase letter
  24&nbsp;#+ (lowercase for the remaining characters).
  25&nbsp;#  Only the *very first line* of an entry begins this way,
  26&nbsp;#+ and that's why the search algorithm below works.
  27&nbsp;
  28&nbsp;
  29&nbsp;
  30&nbsp;if [[ -z $(echo "$1" | sed -n '/^[A-Z]/p') ]]
  31&nbsp;#  Must at least specify word to look up, and
  32&nbsp;#+ it must start with an uppercase letter.
  33&nbsp;then
  34&nbsp;  echo "Usage: `basename $0` Word-to-define [dictionary-file]"
  35&nbsp;  echo
  36&nbsp;  echo "Note: Word to look up must start with capital letter,"
  37&nbsp;  echo "with the rest of the word in lowercase."
  38&nbsp;  echo "--------------------------------------------"
  39&nbsp;  echo "Examples: Abandon, Dictionary, Marking, etc."
  40&nbsp;  exit $E_BADARGS
  41&nbsp;fi
  42&nbsp;
  43&nbsp;
  44&nbsp;if [ -z "$2" ]                            #  May specify different dictionary
  45&nbsp;                                          #+ as an argument to this script.
  46&nbsp;then
  47&nbsp;  dictfile=$DEFAULT_DICTFILE
  48&nbsp;else
  49&nbsp;  dictfile="$2"
  50&nbsp;fi
  51&nbsp;
  52&nbsp;# ---------------------------------------------------------
  53&nbsp;Definition=$(fgrep -A $MAXCONTEXTLINES "$1 \\" "$dictfile")
  54&nbsp;#                  Definitions in form "Word \..."
  55&nbsp;#
  56&nbsp;#  And, yes, "fgrep" is fast enough
  57&nbsp;#+ to search even a very large text file.
  58&nbsp;
  59&nbsp;
  60&nbsp;# Now, snip out just the definition block.
  61&nbsp;
  62&nbsp;echo "$Definition" |
  63&nbsp;sed -n '1,/^[A-Z]/p' |
  64&nbsp;#  Print from first line of output
  65&nbsp;#+ to the first line of the next entry.
  66&nbsp;sed '$d' | sed '$d'
  67&nbsp;#  Delete last two lines of output
  68&nbsp;#+ (blank line and first line of next entry).
  69&nbsp;# ---------------------------------------------------------
  70&nbsp;
  71&nbsp;exit 0
  72&nbsp;
  73&nbsp;# Exercises:
  74&nbsp;# ---------
  75&nbsp;# 1)  Modify the script to accept any type of alphabetic input
  76&nbsp;#   + (uppercase, lowercase, mixed case), and convert it
  77&nbsp;#   + to an acceptable format for processing.
  78&nbsp;#
  79&nbsp;# 2)  Convert the script to a GUI application,
  80&nbsp;#   + using something like 'gdialog' or 'zenity' . . .
  81&nbsp;#     The script will then no longer take its argument(s)
  82&nbsp;#   + from the command line.
  83&nbsp;#
  84&nbsp;# 3)  Modify the script to parse one of the other available
  85&nbsp;#   + Public Domain Dictionaries, such as the U.S. Census Bureau Gazetteer.</PRE
></TD
></TR
></TABLE
><HR></DIV
><P
><A
NAME="AGREPREF"
></A
></P
><P
><B
CLASS="COMMAND"
>agrep</B
> (<I
CLASS="FIRSTTERM"
>approximate
	      grep</I
>) extends the capabilities of
	      <B
CLASS="COMMAND"
>grep</B
> to approximate matching. The search
	      string may differ by a specified number of characters
	      from the resulting matches. This utility is not part of
	      the core Linux distribution.</P
><P
><A
NAME="ZEGREPREF"
></A
></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
>To search compressed files, use
	      <B
CLASS="COMMAND"
>zgrep</B
>, <B
CLASS="COMMAND"
>zegrep</B
>, or
	      <B
CLASS="COMMAND"
>zfgrep</B
>. These also work on non-compressed
	      files, though slower than plain <B
CLASS="COMMAND"
>grep</B
>,
	      <B