assortedtips.html

一本完整的描述Unix Shell 编程的工具书的所有范例

  35 #  Parameterize the filters in lines 11 - 13 (as with $FILTER),
  36 #+ so that they can be specified by passing arguments to a function.
  37 
  38 #  For a slightly different approach to anagramming,
  39&nbsp;#+ see the agram2.sh script.</PRE
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><HR></DIV
><P
>See also <A
HREF="procref1.html#CONSTAT"
>Example 27-3</A
>, <A
HREF="textproc.html#CRYPTOQUOTE"
>Example 12-22</A
>, and <A
HREF="contributed-scripts.html#SOUNDEX"
>Example A-9</A
>.</P
></LI
><LI
><P
>Use <SPAN
CLASS="QUOTE"
>"<A
HREF="here-docs.html#ANONHEREDOC0"
>anonymous here
	    documents</A
>"</SPAN
> to comment out blocks of code,
	    to save having to individually comment out each line with
	    a <SPAN
CLASS="TOKEN"
>#</SPAN
>.  See <A
HREF="here-docs.html#COMMENTBLOCK"
>Example 17-11</A
>.</P
></LI
><LI
><P
>Running a script on a machine that relies on a command
	    that might not be installed is dangerous. Use <A
HREF="filearchiv.html#WHATISREF"
>whatis</A
> to avoid potential problems
	    with this.</P
><P
>	    <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;CMD=command1                 # First choice.
   2&nbsp;PlanB=command2               # Fallback option.
   3&nbsp;
   4&nbsp;command_test=$(whatis "$CMD" | grep 'nothing appropriate')
   5&nbsp;#  If 'command1' not found on system , 'whatis' will return
   6&nbsp;#+ "command1: nothing appropriate."
   7&nbsp;#
   8&nbsp;#  A safer alternative is:
   9&nbsp;#     command_test=$(whereis "$CMD" | grep \/)
  10&nbsp;#  But then the sense of the following test would have to be reversed,
  11&nbsp;#+ since the $command_test variable holds content only if
  12&nbsp;#+ the $CMD exists on the system.
  13&nbsp;#     (Thanks, bojster.)
  14&nbsp;
  15&nbsp;
  16&nbsp;if [[ -z "$command_test" ]]  # Check whether command present.
  17&nbsp;then
  18&nbsp;  $CMD option1 option2       #  Run command1 with options.
  19&nbsp;else                         #  Otherwise,
  20&nbsp;  $PlanB                     #+ run command2. 
  21&nbsp;fi</PRE
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>
          </P
></LI
><LI
><P
>An <A
HREF="tests.html#IFGREPREF"
>if-grep test</A
> may not
	    return expected results in an error case, when text is output to
	    <TT
CLASS="FILENAME"
>stderr</TT
>, rather that
	    <TT
CLASS="FILENAME"
>stdout</TT
>.
	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;if ls -l nonexistent_filename | grep -q 'No such file or directory'
   2&nbsp;  then echo "File \"nonexistent_filename\" does not exist."
   3&nbsp;fi</PRE
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></P
><P
><A
HREF="io-redirection.html#IOREDIRREF"
>Redirecting</A
>
	    <TT
CLASS="FILENAME"
>stderr</TT
> to <TT
CLASS="FILENAME"
>stdout</TT
> fixes
	    this.
	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;if ls -l nonexistent_filename 2&#62;&#38;1 | grep -q 'No such file or directory'
   2&nbsp;#                             ^^^^
   3&nbsp;  then echo "File \"nonexistent_filename\" does not exist."
   4&nbsp;fi
   5&nbsp;
   6&nbsp;# Thanks, Chris Martin, for pointing this out.</PRE
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></P
></LI
><LI
><P
>The <A
HREF="extmisc.html#RUNPARTSREF"
>run-parts</A
>
	    command is handy for running a set of command
	    scripts in sequence, particularly in combination
	    with <A
HREF="system.html#CRONREF"
>cron</A
> or <A
HREF="timedate.html#ATREF"
>at</A
>.</P
></LI
><LI
><P
>It would be nice to be able to invoke X-Windows widgets
	    from a shell script. There happen to exist
	    several packages that purport to do so, namely
	    <I
CLASS="EMPHASIS"
>Xscript</I
>, <I
CLASS="EMPHASIS"
>Xmenu</I
>,
	    and <I
CLASS="EMPHASIS"
>widtools</I
>.	The first two of
	    these no longer seem to be maintained.  Fortunately, it is
	    still possible to obtain <I
CLASS="EMPHASIS"
>widtools</I
> <A
HREF="http://www.batse.msfc.nasa.gov/~mallozzi/home/software/xforms/src/widtools-2.0.tgz"
TARGET="_top"
>here</A
>.
	    </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
>The <I
CLASS="EMPHASIS"
>widtools</I
> (widget tools)
	    package requires the <I
CLASS="EMPHASIS"
>XForms</I
> library to
	    be installed. Additionally, the <A
HREF="filearchiv.html#MAKEFILEREF"
>Makefile</A
> needs some judicious
	    editing before the package will build on a typical Linux
	    system. Finally, three of the six widgets offered do not work
	    (and, in fact, segfault).</P
></TD
></TR
></TABLE
></DIV
><P
><A
NAME="DIALOGREF"
></A
></P
><P
>The <I
CLASS="EMPHASIS"
>dialog</I
> family of tools offers a method
	    of calling <SPAN
CLASS="QUOTE"
>"dialog"</SPAN
> widgets from a shell script. The
	    original <B
CLASS="COMMAND"
>dialog</B
> utility works in a text
	    console, but its successors, <B
CLASS="COMMAND"
>gdialog</B
>,
	    <B
CLASS="COMMAND"
>Xdialog</B
>, and <B
CLASS="COMMAND"
>kdialog</B
>
	    use X-Windows-based widget sets.</P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="DIALOG"
></A
><P
><B
>Example 33-19. <B
CLASS="COMMAND"
>Widgets invoked from a shell script</B
></B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# dialog.sh: Using 'gdialog' widgets.
   3&nbsp;# Must have 'gdialog' installed on your system to run this script.
   4&nbsp;# Version 1.1 (corrected 04/05/05)
   5&nbsp;
   6&nbsp;# This script was inspired by the following article.
   7&nbsp;#     "Scripting for X Productivity," by Marco Fioretti,
   8&nbsp;#      LINUX JOURNAL, Issue 113, September 2003, pp. 86-9.
   9&nbsp;# Thank you, all you good people at LJ.
  10&nbsp;
  11&nbsp;
  12&nbsp;# Input error in dialog box.
  13&nbsp;E_INPUT=65
  14&nbsp;# Dimensions of display, input widgets.
  15&nbsp;HEIGHT=50
  16&nbsp;WIDTH=60
  17&nbsp;
  18&nbsp;# Output file name (constructed out of script name).
  19&nbsp;OUTFILE=$0.output
  20&nbsp;
  21&nbsp;# Display this script in a text widget.
  22&nbsp;gdialog --title "Displaying: $0" --textbox $0 $HEIGHT $WIDTH
  23&nbsp;
  24&nbsp;
  25&nbsp;
  26&nbsp;# Now, we'll try saving input in a file.
  27&nbsp;echo -n "VARIABLE=" &#62; $OUTFILE
  28&nbsp;gdialog --title "User Input" --inputbox "Enter variable, please:" \
  29&nbsp;$HEIGHT $WIDTH 2&#62;&#62; $OUTFILE
  30&nbsp;
  31&nbsp;
  32&nbsp;if [ "$?" -eq 0 ]
  33&nbsp;# It's good practice to check exit status.
  34&nbsp;then
  35&nbsp;  echo "Executed \"dialog box\" without errors."
  36&nbsp;else
  37&nbsp;  echo "Error(s) in \"dialog box\" execution."
  38&nbsp;        # Or, clicked on "Cancel", instead of "OK" button.
  39&nbsp;  rm $OUTFILE
  40&nbsp;  exit $E_INPUT
  41&nbsp;fi
  42&nbsp;
  43&nbsp;
  44&nbsp;
  45&nbsp;# Now, we'll retrieve and display the saved variable.
  46&nbsp;. $OUTFILE   # 'Source' the saved file.
  47&nbsp;echo "The variable input in the \"input box\" was: "$VARIABLE""
  48&nbsp;
  49&nbsp;
  50&nbsp;rm $OUTFILE  # Clean up by removing the temp file.
  51&nbsp;             # Some applications may need to retain this file.
  52&nbsp;
  53&nbsp;exit $?</PRE
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><HR></DIV
><P
>For other methods of scripting with widgets, try
	    <I
CLASS="EMPHASIS"
>Tk</I
> or <I
CLASS="EMPHASIS"
>wish</I
>
	    (<I
CLASS="EMPHASIS"
>Tcl</I
> derivatives),
	    <I
CLASS="EMPHASIS"
>PerlTk</I
> (Perl with Tk extensions),
	    <I
CLASS="EMPHASIS"
>tksh</I
> (ksh with Tk extensions),
	    <I
CLASS="EMPHASIS"
>XForms4Perl</I
> (Perl with XForms
	    extensions), <I
CLASS="EMPHASIS"
>Gtk-Perl</I
> (Perl with Gtk
	    extensions), or <I
CLASS="EMPHASIS"
>PyQt</I
> (Python with
	    Qt extensions).</P
></LI
><LI
><P
>For doing multiple revisions on a complex script, use the
	    <I
CLASS="EMPHASIS"
>rcs</I
> Revision Control System package.</P
><P
> Among
	    other benefits of this is automatically updated ID
	    header tags. The <B
CLASS="COMMAND"
>co</B
> command in
	    <I
CLASS="EMPHASIS"
>rcs</I
> does a parameter replacement of
	    certain reserved key words, for example, replacing
	    <TT
CLASS="PARAMETER"
><I
>#$Id$</I
></TT
> in a script with something like:
	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#$Id: hello-world.sh,v 1.1 2004/10/16 02:43:05 bozo Exp $</PRE
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