string-manipulation.html

Shall高级编程

	    <TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
>.</P
></DD
><DT
>${string##substring}</DT
><DD
><P
>Strips longest match of
	    <TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> from
	    <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>front</I
></SPAN
> of
	    <TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
>.</P
><P
>  
	  <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;stringZ=abcABC123ABCabc
   2&nbsp;#       |----|
   3&nbsp;#       |----------|
   4&nbsp;
   5&nbsp;echo ${stringZ#a*C}      # 123ABCabc
   6&nbsp;# Strip out shortest match between 'a' and 'C'.
   7&nbsp;
   8&nbsp;echo ${stringZ##a*C}     # abc
   9&nbsp;# Strip out longest match between 'a' and 'C'.</PRE
></TD
></TR
></TABLE
>
	  </P
></DD
><DT
>${string%substring}</DT
><DD
><P
>Strips shortest match of
	    <TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> from
	    <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>back</I
></SPAN
> of
	    <TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
>.</P
><P
>For example:
	    <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;# Rename all filenames in $PWD with "TXT" suffix to a "txt" suffix.
   2&nbsp;# For example, "file1.TXT" becomes "file1.txt" . . .
   3&nbsp;
   4&nbsp;SUFF=TXT
   5&nbsp;suff=txt
   6&nbsp;
   7&nbsp;for i in $(ls *.$SUFF)
   8&nbsp;do
   9&nbsp;  mv -f $i ${i%.$SUFF}.$suff
  10&nbsp;  #  Leave unchanged everything *except* the shortest pattern match
  11&nbsp;  #+ starting from the right-hand-side of the variable $i . . .
  12&nbsp;done ### This could be condensed into a "one-liner" if desired.
  13&nbsp;
  14&nbsp;# Thank you, Rory Winston.</PRE
></TD
></TR
></TABLE
>
	  </P
></DD
><DT
>${string%%substring}</DT
><DD
><P
>Strips longest match of
	    <TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> from
	    <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>back</I
></SPAN
> of
	    <TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
>.</P
><P
>  
	  <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;stringZ=abcABC123ABCabc
   2&nbsp;#                    ||
   3&nbsp;#        |------------|
   4&nbsp;
   5&nbsp;echo ${stringZ%b*c}      # abcABC123ABCa
   6&nbsp;# Strip out shortest match between 'b' and 'c', from back of $stringZ.
   7&nbsp;
   8&nbsp;echo ${stringZ%%b*c}     # a
   9&nbsp;# Strip out longest match between 'b' and 'c', from back of $stringZ.</PRE
></TD
></TR
></TABLE
>
	  </P
><P
>This operator is useful for generating filenames.</P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="CVT"
></A
><P
><B
>Example 9-12. Converting graphic file formats, with filename change</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;#  cvt.sh:
   3&nbsp;#  Converts all the MacPaint image files in a directory to "pbm" format.
   4&nbsp;
   5&nbsp;#  Uses the "macptopbm" binary from the "netpbm" package,
   6&nbsp;#+ which is maintained by Brian Henderson ([e-mail]).
   7&nbsp;#  Netpbm is a standard part of most Linux distros.
   8&nbsp;
   9&nbsp;OPERATION=macptopbm
  10&nbsp;SUFFIX=pbm          # New filename suffix. 
  11&nbsp;
  12&nbsp;if [ -n "$1" ]
  13&nbsp;then
  14&nbsp;  directory=$1      # If directory name given as a script argument...
  15&nbsp;else
  16&nbsp;  directory=$PWD    # Otherwise use current working directory.
  17&nbsp;fi  
  18&nbsp;  
  19&nbsp;#  Assumes all files in the target directory are MacPaint image files,
  20&nbsp;#+ with a ".mac" filename suffix.
  21&nbsp;
  22&nbsp;for file in $directory/*    # Filename globbing.
  23&nbsp;do
  24&nbsp;  filename=${file%.*c}      #  Strip ".mac" suffix off filename
  25&nbsp;                            #+ ('.*c' matches everything
  26&nbsp;			    #+ between '.' and 'c', inclusive).
  27&nbsp;  $OPERATION $file &#62; "$filename.$SUFFIX"
  28&nbsp;                            # Redirect conversion to new filename.
  29&nbsp;  rm -f $file               # Delete original files after converting.   
  30&nbsp;  echo "$filename.$SUFFIX"  # Log what is happening to stdout.
  31&nbsp;done
  32&nbsp;
  33&nbsp;exit 0
  34&nbsp;
  35&nbsp;# Exercise:
  36&nbsp;# --------
  37&nbsp;#  As it stands, this script converts *all* the files in the current
  38&nbsp;#+ working directory.
  39&nbsp;#  Modify it to work *only* on files with a ".mac" suffix.</PRE
></TD
></TR
></TABLE
><HR></DIV
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="RA2OGG"
></A
><P
><B
>Example 9-13. Converting streaming audio files to
	      <I
CLASS="FIRSTTERM"
>ogg</I
></B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# ra2ogg.sh: Convert streaming audio files (*.ra) to ogg.
   3&nbsp;
   4&nbsp;# Uses the "mplayer" media player program:
   5&nbsp;#      http://www.mplayerhq.hu/homepage
   6&nbsp;#      Appropriate codecs may need to be installed for this script to work.
   7&nbsp;# Uses the "ogg" library and "oggenc":
   8&nbsp;#      http://www.xiph.org/
   9&nbsp;
  10&nbsp;
  11&nbsp;OFILEPREF=${1%%ra}      # Strip off the "ra" suffix.
  12&nbsp;OFILESUFF=wav           # Suffix for wav file.
  13&nbsp;OUTFILE="$OFILEPREF""$OFILESUFF"
  14&nbsp;E_NOARGS=65
  15&nbsp;
  16&nbsp;if [ -z "$1" ]          # Must specify a filename to convert.
  17&nbsp;then
  18&nbsp;  echo "Usage: `basename $0` [filename]"
  19&nbsp;  exit $E_NOARGS
  20&nbsp;fi
  21&nbsp;
  22&nbsp;
  23&nbsp;##########################################################################
  24&nbsp;mplayer "$1" -ao pcm:file=$OUTFILE
  25&nbsp;oggenc "$OUTFILE"  # Correct file extension automatically added by oggenc.
  26&nbsp;##########################################################################
  27&nbsp;
  28&nbsp;rm "$OUTFILE"      # Delete intermediate *.wav file.
  29&nbsp;                   # If you want to keep it, comment out above line.
  30&nbsp;
  31&nbsp;exit $?
  32&nbsp;
  33&nbsp;#  Note:
  34&nbsp;#  ----
  35&nbsp;#  On a Website, simply clicking on a *.ram streaming audio file
  36&nbsp;#+ usually only downloads the URL of the actual audio file, the *.ra file.
  37&nbsp;#  You can then use "wget" or something similar
  38&nbsp;#+ to download the *.ra file itself.
  39&nbsp;
  40&nbsp;
  41&nbsp;#  Exercises:
  42&nbsp;#  ---------
  43&nbsp;#  As is, this script converts only *.ra filenames.
  44&nbsp;#  Add flexibility by permitting use of *.ram and other filenames.
  45&nbsp;#
  46&nbsp;#  If you're really ambitious, expand the script
  47&nbsp;#+ to do automatic downloads and conversions of streaming audio files.
  48&nbsp;#  Given a URL, batch download streaming audio files (using "wget")
  49&nbsp;#+ and convert them.</PRE
></TD
></TR
></TABLE
><HR></DIV
><P
><A
NAME="GETOPTSIMPLE1"
></A
></P
><P
>A simple emulation of <A
HREF="extmisc.html#GETOPTY"
>getopt</A
>
	    using substring extraction constructs.</P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="GETOPTSIMPLE"
></A
><P
><B
>Example 9-14. Emulating <I
CLASS="FIRSTTERM"
>getopt</I
></B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# getopt-simple.sh
   3&nbsp;# Author: Chris Morgan
   4&nbsp;# Used in the ABS Guide with permission.
   5&nbsp;
   6&nbsp;
   7&nbsp;getopt_simple()
   8&nbsp;{
   9&nbsp;    echo "getopt_simple()"
  10&nbsp;    echo "Parameters are '$*'"
  11&nbsp;    until [ -z "$1" ]
  12&nbsp;    do
  13&nbsp;      echo "Processing parameter of: '$1'"
  14&nbsp;      if [ ${1:0:1} = '/' ]
  15&nbsp;      then
  16&nbsp;          tmp=${1:1}               # Strip off leading '/' . . .
  17&nbsp;          parameter=${tmp%%=*}     # Extract name.
  18&nbsp;          value=${tmp##*=}         # Extract value.
  19&nbsp;          echo "Parameter: '$parameter', value: '$value'"
  20&nbsp;          eval $parameter=$value
  21&nbsp;      fi
  22&nbsp;      shift
  23&nbsp;    done
  24&nbsp;}
  25&nbsp;
  26&nbsp;# Pass all options to getopt_simple().
  27&nbsp;getopt_simple $*
  28&nbsp;
  29&nbsp;echo "test is '$test'"
  30&nbsp;echo "test2 is '$test2'"
  31&nbsp;
  32&nbsp;exit 0
  33&nbsp;
  34&nbsp;---
  35&nbsp;
  36&nbsp;sh getopt_example.sh /test=value1 /test2=value2
  37&nbsp;
  38&nbsp;Parameters are '/test=value1 /test2=value2'
  39&nbsp;Processing parameter of: '/test=value1'
  40&nbsp;Parameter: 'test', value: 'value1'
  41&nbsp;Processing parameter of: '/test2=value2'
  42&nbsp;Parameter: 'test2', value: 'value2'
  43&nbsp;test is 'value1'
  44&nbsp;test2 is 'value2'</PRE
></TD
></TR
></TABLE
><HR></DIV
></DD
></DL
></DIV
><DIV
CLASS="VARIABLELIST"
><P
><B
>Substring Replacement</B
></P
><DL
><DT
><A
NAME="SUBSTRREPL00"
></A
>${string/substring/replacement}</DT
><DD
><P
>Replace first match of
	    <TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> with
	    <TT
CLASS="REPLACEABLE"
><I
>$replacement</I
></TT
>.</P
></DD
><DT
><A
NAME="SUBSTRREPL01"
></A
>${string//substring/replacement}</DT
><DD
><P
>Replace all matches of
	    <TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> with
	    <TT
CLASS="REPLACEABLE"
><I
>$replacement</I
></TT
>.</P
><P
>  
	  <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;stringZ=abcABC123ABCabc
   2&nbsp;
   3&nbsp;echo ${stringZ/abc/xyz}           # xyzABC123ABCabc
   4&nbsp;                                  # Replaces first match of 'abc' with 'xyz'.
   5&nbsp;
   6&nbsp;echo ${stringZ//abc/xyz}          # xyzABC123ABCxyz
   7&nbsp;                                  # Replaces all matches of 'abc' with # 'xyz'.</PRE
></TD
></TR
></TABLE
>
	  </P
></DD
><DT
><A
NAME="SUBSTRREPL02"
></A
>${string/#substring/replacement}</DT
><DD
><P
>If <TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> matches
	    <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>front</I
></SPAN
> end of
	    <TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
>, substitute
	    <TT
CLASS="REPLACEABLE"
><I
>$replacement</I
></TT
> for
	    <TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
>.</P
></DD
><DT
><A
NAME="SUBSTRREPL03"
></A
>${string/%substring/replacement}</DT
><DD
><P
>If <TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
> matches
	    <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>back</I
></SPAN
> end of
	    <TT
CLASS="REPLACEABLE"
><I
>$string</I
></TT
>, substitute
	    <TT
CLASS="REPLACEABLE"
><I
>$replacement</I
></TT
> for
	    <TT
CLASS="REPLACEABLE"
><I
>$substring</I
></TT
>.</P
><P
>  
          <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;stringZ=abcABC123ABCabc
   2&nbsp;
   3&nbsp;echo ${stringZ/#abc/XYZ}          # XYZABC123ABCabc
   4&nbsp;                                  # Replaces front-end match of 'abc' with 'XYZ'.
   5&nbsp;
   6&nbsp;echo ${stringZ/%abc/XYZ}          # abcABC123ABCXYZ
   7&nbsp;                                  # Replaces back-end match of 'abc' with 'XYZ'.</PRE
></TD
></TR
></TABLE
>
	  </P
></DD
></DL
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AWKSTRINGMANIP"
></A
>9.2.1. Manipulating strings using awk</H2
><P
><A
NAME="AWKSTRINGMANIP2"
></A
></P
><P
>A Bash script may invoke the string manipulation facilities of
	    <A
HREF="awk.html#AWKREF"
>awk</A
> as an alternative to using its
	    built-in operations.</P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="SUBSTRINGEX"
></A
><P
><B
>Example 9-15. Alternate ways of extracting substrings</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# substring-extraction.sh
   3&nbsp;
   4&nbsp;String=23skidoo1
   5&nbsp;#      012345678    Bash
   6&nbsp;#      123456789    awk
   7&nbsp;# Note different string indexing system:
   8&nbsp;# Bash numbers first character of string as '0'.
   9&nbsp;# Awk  numbers first character of string as '1'.
  10&nbsp;
  11&nbsp;echo ${String:2:4} # position 3 (0-1-2), 4 characters long
  12&nbsp;                                         # skid
  13&nbsp;
  14&nbsp;# The awk equivalent of ${string:pos:length} is substr(string,pos,length).
  15&nbsp;echo | awk '
  16&nbsp;{ print substr("'"${String}"'",3,4)      # skid
  17&nbsp;}
  18&nbsp;'
  19&nbsp;#  Piping an empty "echo" to awk gives it dummy input,
  20&nbsp;#+ and thus makes it unnecessary to supply a filename.
  21&nbsp;
  22&nbsp;exit 0</PRE
></TD
></TR
></TABLE
><HR></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="STRFDISC"
></A
>9.2.2. Further Discussion</H2
><P
>For more on string manipulation in scripts, refer to <A
HREF="parameter-substitution.html"
>Section 9.3</A
> and the
       <A
HREF="moreadv.html#EXPEXTRSUB"
>relevant section</A
> of the <A
HREF="moreadv.html#EXPRREF"
>expr</A
> command listing. For script examples,
       see: <OL
TYPE="1"
><LI
><P
><A
HREF="moreadv.html#EX45"
>Example 15-9</A
></P
></LI
><LI
><P
><A
HREF="parameter-substitution.html#LENGTH"
>Example 9-18</A
></P
></LI
><LI
><P
><A
HREF="parameter-substitution.html#PATTMATCHING"
>Example 9-19</A
></P
></LI
><LI
><P
><A
HREF="parameter-substitution.html#RFE"
>Example 9-20</A
></P
></LI
><LI
><P
><A
HREF="parameter-substitution.html#VARMATCH"
>Example 9-22</A
></P
></LI
><LI
><P
><A
HREF="contributed-scripts.html#INSERTIONSORT"
>Example A-38</A
></P
></LI
></OL
>
      </P
></DIV
></DIV
><H3
CLASS="FOOTNOTES"
>Notes</H3
><TABLE
BORDER="0"
CLASS="FOOTNOTES"
WIDTH="100%"
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN5008"
HREF="string-manipulation.html#AEN5008"
>[1]</A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>This applies to either command-line
	       arguments or parameters passed to a <A
HREF="functions.html#FUNCTIONREF"
>function</A
>.</P
></TD
></TR
></TABLE
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