textproc.html

Shall高级编程

CLASS="COMMAND"
>egrep</B
>, <B
CLASS="COMMAND"
>fgrep</B
>.
	      They are handy for searching through a mixed set of files,
	      some compressed, some not.</P
><P
><A
NAME="BZGREPREF"
></A
></P
><P
>To search <A
HREF="filearchiv.html#BZIPREF"
>bzipped</A
>
	      files, use <B
CLASS="COMMAND"
>bzgrep</B
>.</P
></TD
></TR
></TABLE
></DIV
></DD
><DT
><A
NAME="LOOKREF"
></A
><B
CLASS="COMMAND"
>look</B
></DT
><DD
><P
>The command <B
CLASS="COMMAND"
>look</B
> works like
	      <B
CLASS="COMMAND"
>grep</B
>, but does a lookup on
	      a <SPAN
CLASS="QUOTE"
>"dictionary,"</SPAN
> a sorted word list.
	      By default, <B
CLASS="COMMAND"
>look</B
> searches for a match
	      in <TT
CLASS="FILENAME"
>/usr/dict/words</TT
>, but a different
	      dictionary file may be specified.</P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="LOOKUP"
></A
><P
><B
>Example 15-19. Checking words in a list for validity</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# lookup: Does a dictionary lookup on each word in a data file.
   3&nbsp;
   4&nbsp;file=words.data  # Data file from which to read words to test.
   5&nbsp;
   6&nbsp;echo
   7&nbsp;
   8&nbsp;while [ "$word" != end ]  # Last word in data file.
   9&nbsp;do               # ^^^
  10&nbsp;  read word      # From data file, because of redirection at end of loop.
  11&nbsp;  look $word &#62; /dev/null  # Don't want to display lines in dictionary file.
  12&nbsp;  lookup=$?      # Exit status of 'look' command.
  13&nbsp;
  14&nbsp;  if [ "$lookup" -eq 0 ]
  15&nbsp;  then
  16&nbsp;    echo "\"$word\" is valid."
  17&nbsp;  else
  18&nbsp;    echo "\"$word\" is invalid."
  19&nbsp;  fi  
  20&nbsp;
  21&nbsp;done &#60;"$file"    # Redirects stdin to $file, so "reads" come from there.
  22&nbsp;
  23&nbsp;echo
  24&nbsp;
  25&nbsp;exit 0
  26&nbsp;
  27&nbsp;# ----------------------------------------------------------------
  28&nbsp;# Code below line will not execute because of "exit" command above.
  29&nbsp;
  30&nbsp;
  31&nbsp;# Stephane Chazelas proposes the following, more concise alternative:
  32&nbsp;
  33&nbsp;while read word &#38;&#38; [[ $word != end ]]
  34&nbsp;do if look "$word" &#62; /dev/null
  35&nbsp;   then echo "\"$word\" is valid."
  36&nbsp;   else echo "\"$word\" is invalid."
  37&nbsp;   fi
  38&nbsp;done &#60;"$file"
  39&nbsp;
  40&nbsp;exit 0</PRE
></TD
></TR
></TABLE
><HR></DIV
></DD
><DT
><B
CLASS="COMMAND"
>sed</B
>, <B
CLASS="COMMAND"
>awk</B
></DT
><DD
><P
>Scripting languages especially suited for parsing text
	      files and command output. May be embedded singly or in
	      combination in pipes and shell scripts.</P
></DD
><DT
><B
CLASS="COMMAND"
><A
HREF="sedawk.html#SEDREF"
>sed</A
></B
></DT
><DD
><P
>Non-interactive <SPAN
CLASS="QUOTE"
>"stream editor"</SPAN
>, permits using
	      many <B
CLASS="COMMAND"
>ex</B
> commands in <A
HREF="timedate.html#BATCHPROCREF"
>batch</A
> mode. It finds many
	      uses in shell scripts.</P
></DD
><DT
><B
CLASS="COMMAND"
><A
HREF="awk.html#AWKREF"
>awk</A
></B
></DT
><DD
><P
>Programmable file extractor and formatter, good for
	      manipulating and/or extracting fields (columns) in
	      structured text files. Its syntax is similar to C.</P
></DD
><DT
><A
NAME="WCREF"
></A
><B
CLASS="COMMAND"
>wc</B
></DT
><DD
><P
><I
CLASS="FIRSTTERM"
>wc</I
> gives a <SPAN
CLASS="QUOTE"
>"word
	      count"</SPAN
> on a file or I/O stream:

	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash $ </TT
><TT
CLASS="USERINPUT"
><B
>wc /usr/share/doc/sed-4.1.2/README</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>13  70  447 README</TT
>
 [13 lines  70 words  447 characters]</PRE
></TD
></TR
></TABLE
></P
><P
><TT
CLASS="USERINPUT"
><B
>wc -w</B
></TT
> gives only the word count.</P
><P
><TT
CLASS="USERINPUT"
><B
>wc -l</B
></TT
> gives only the line count.</P
><P
><TT
CLASS="USERINPUT"
><B
>wc -c</B
></TT
> gives only the byte count.</P
><P
><TT
CLASS="USERINPUT"
><B
>wc -m</B
></TT
> gives only the character count.</P
><P
><TT
CLASS="USERINPUT"
><B
>wc -L</B
></TT
> gives only the length of the longest line.</P
><P
>Using <B
CLASS="COMMAND"
>wc</B
> to count how many
	    <TT
CLASS="FILENAME"
>.txt</TT
> files are in current working directory:
	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;$ ls *.txt | wc -l
   2&nbsp;#  Will work as long as none of the "*.txt" files
   3&nbsp;#+ have a linefeed embedded in their name.
   4&nbsp;
   5&nbsp;#  Alternative ways of doing this are:
   6&nbsp;#      find . -maxdepth 1 -name \*.txt -print0 | grep -cz .
   7&nbsp;#      (shopt -s nullglob; set -- *.txt; echo $#)
   8&nbsp;
   9&nbsp;#  Thanks, S.C.</PRE
></TD
></TR
></TABLE
>
	    </P
><P
>Using <B
CLASS="COMMAND"
>wc</B
> to total up the size of all the
	      files whose names begin with letters in the range d - h
	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>wc [d-h]* | grep total | awk '{print $3}'</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>71832</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
><P
>Using <B
CLASS="COMMAND"
>wc</B
> to count the instances of the
	      word <SPAN
CLASS="QUOTE"
>"Linux"</SPAN
> in the main source file for
	      this book.
	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>grep Linux abs-book.sgml | wc -l</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>50</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
><P
>See also <A
HREF="filearchiv.html#EX52"
>Example 15-38</A
> and <A
HREF="redircb.html#REDIR4"
>Example 19-8</A
>.</P
><P
>Certain commands include some of the
	      functionality of <B
CLASS="COMMAND"
>wc</B
> as options.
	      
	    <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;... | grep foo | wc -l
   2&nbsp;# This frequently used construct can be more concisely rendered.
   3&nbsp;
   4&nbsp;... | grep -c foo
   5&nbsp;# Just use the "-c" (or "--count") option of grep.
   6&nbsp;
   7&nbsp;# Thanks, S.C.</PRE
></TD
></TR
></TABLE
></P
></DD
><DT
><A
NAME="TRREF"
></A
><B
CLASS="COMMAND"
>tr</B
></DT
><DD
><P
>character translation filter.</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
><A
HREF="special-chars.html#UCREF"
>Must use quoting and/or
	      brackets</A
>, as appropriate. Quotes prevent the
	      shell from reinterpreting the special characters in
	      <B
CLASS="COMMAND"
>tr</B
> command sequences. Brackets should be
	      quoted to prevent expansion by the shell.  </P
></TD
></TR
></TABLE
></DIV
><P
>Either <TT
CLASS="USERINPUT"
><B
>tr "A-Z" "*" &#60;filename</B
></TT
>
	      or <TT
CLASS="USERINPUT"
><B
>tr A-Z \* &#60;filename</B
></TT
> changes
	      all the uppercase letters in <TT
CLASS="FILENAME"
>filename</TT
>
	      to asterisks (writes to <TT
CLASS="FILENAME"
>stdout</TT
>).
	      On some systems this may not work, but <TT
CLASS="USERINPUT"
><B
>tr A-Z
	      '[**]'</B
></TT
> will.</P
><P
><A
NAME="TROPTIONS"
></A
></P
><P
>The <TT
CLASS="OPTION"
>-d</TT
> option deletes a range of
	      characters.
	    <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;echo "abcdef"                 # abcdef
   2&nbsp;echo "abcdef" | tr -d b-d     # aef
   3&nbsp;
   4&nbsp;
   5&nbsp;tr -d 0-9 &#60;filename
   6&nbsp;# Deletes all digits from the file "filename".</PRE
></TD
></TR
></TABLE
></P
><P
>The <TT
CLASS="OPTION"
>--squeeze-repeats</TT
> (or
              <TT
CLASS="OPTION"
>-s</TT
>) option deletes all but the
              first instance of a string of consecutive characters.
              This option is useful for removing excess <A
HREF="special-chars.html#WHITESPACEREF"
>whitespace</A
>.



	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>echo "XXXXX" | tr --squeeze-repeats 'X'</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>X</TT
></PRE
></TD
></TR
></TABLE
></P
><P
>The <TT
CLASS="OPTION"
>-c</TT
> <SPAN
CLASS="QUOTE"
>"complement"</SPAN
>
	      option <I
CLASS="FIRSTTERM"
>inverts</I
> the character set to
	      match. With this option, <B
CLASS="COMMAND"
>tr</B
> acts only
	      upon those characters <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>not</I
></SPAN
> matching
	      the specified set.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>echo "acfdeb123" | tr -c b-d +</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>+c+d+b++++</TT
></PRE
></TD
></TR
></TABLE
>
            </P
><P
>Note that <B
CLASS="COMMAND"
>tr</B
> recognizes <A
HREF="regexp.html#POSIXREF"
>POSIX character classes</A
>.
	         <A
NAME="AEN10535"
HREF="#FTN.AEN10535"
>[1]</A
>
	      </P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>echo "abcd2ef1" | tr '[:alpha:]' -</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>----2--1</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="EX49"
></A
><P
><B
>Example 15-20. <I
CLASS="FIRSTTERM"
>toupper</I
>: Transforms a file
	      to all uppercase.</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# Changes a file to all uppercase.
   3&nbsp;
   4&nbsp;E_BADARGS=65
   5&nbsp;
   6&nbsp;if [ -z "$1" ]  # Standard check for command line arg.
   7&nbsp;then
   8&nbsp;  echo "Usage: `basename $0` filename"
   9&nbsp;  exit $E_BADARGS
  10&nbsp;fi  
  11&nbsp;
  12&nbsp;tr a-z A-Z &#60;"$1"
  13&nbsp;
  14&nbsp;# Same effect as above, but using POSIX character set notation:
  15&nbsp;#        tr '[:lower:]' '[:upper:]' &#60;"$1"
  16&nbsp;# Thanks, S.C.
  17&nbsp;
  18&nbsp;exit 0
  19&nbsp;
  20&nbsp;#  Exercise:
  21&nbsp;#  Rewrite this script to give the option of changing a file
  22&nbsp;#+ to *either* upper or lowercase.</PRE
></TD
></TR
></TABLE
><HR></DIV
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="LOWERCASE"
></A
><P
><B
>Example 15-21. <I
CLASS="FIRSTTERM"
>lowercase</I
>: Changes all
	      filenames in working directory to lowercase.</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;#
   3&nbsp;#  Changes every filename in working directory to all lowercase.
   4&nbsp;#
   5&nbsp;#  Inspired by a script of John Dubois,
   6&nbsp;#+ which was translated into Bash by Chet Ramey,
   7&nbsp;#+ and considerably simplified by the author of the ABS Guide.
   8&nbsp;
   9&nbsp;
  10&nbsp;for filename in *                # Traverse all files in directory.
  11&nbsp;do
  12&nbsp;   fname=`basename $filename`
  13&nbsp;   n=`echo $fname | tr A-Z a-z`  # Change name to lowercase.
  14&nbsp;   if [ "$fname" != "$n" ]       # Rename only files not already lowercase.
  15&nbsp;   then
  16&nbsp;     mv $fname $n
  17&nbsp;   fi  
  18&nbsp;done   
  19&nbsp;
  20&nbsp;exit $?
  21&nbsp;
  22&nbsp;
  23&nbsp;# Code below this line will not execute because of "exit".
  24&nbsp;#--------------------------------------------------------#
  25&nbsp;# To run it, delete script above line.
  26&nbsp;
  27&nbsp;# The above script will not work on filenames containing blanks or newlines.
  28&nbsp;# Stephane Chazelas therefore suggests the following alternative:
  29&nbsp;