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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><HTML><HEAD><TITLE>Shell Wrappers</TITLE><METANAME="GENERATOR"CONTENT="Modular DocBook HTML Stylesheet Version 1.76b+"><LINKREL="HOME"TITLE="Advanced Bash-Scripting Guide"HREF="index.html"><LINKREL="UP"TITLE="Miscellany"HREF="miscellany.html"><LINKREL="PREVIOUS"TITLE="Operator Precedence"HREF="opprecedence.html"><LINKREL="NEXT"TITLE="Tests and Comparisons: Alternatives"HREF="testsandcomparisons.html"><METAHTTP-EQUIV="Content-Style-Type"CONTENT="text/css"><LINKREL="stylesheet"HREF="common/kde-common.css"TYPE="text/css"><METAHTTP-EQUIV="Content-Type"CONTENT="text/html; charset=iso-8859-1"><METAHTTP-EQUIV="Content-Language"CONTENT="en"><LINKREL="stylesheet"HREF="common/kde-localised.css"TYPE="text/css"TITLE="KDE-English"><LINKREL="stylesheet"HREF="common/kde-default.css"TYPE="text/css"TITLE="KDE-Default"></HEAD><BODYCLASS="SECT1"BGCOLOR="#FFFFFF"TEXT="#000000"LINK="#AA0000"VLINK="#AA0055"ALINK="#AA0000"STYLE="font-family: sans-serif;"><DIVCLASS="NAVHEADER"><TABLESUMMARY="Header navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><THCOLSPAN="3"ALIGN="center">Advanced Bash-Scripting Guide: An in-depth exploration of the art of shell scripting</TH></TR><TR><TDWIDTH="10%"ALIGN="left"VALIGN="bottom"><AHREF="opprecedence.html"ACCESSKEY="P">Prev</A></TD><TDWIDTH="80%"ALIGN="center"VALIGN="bottom">Chapter 33. Miscellany</TD><TDWIDTH="10%"ALIGN="right"VALIGN="bottom"><AHREF="testsandcomparisons.html"ACCESSKEY="N">Next</A></TD></TR></TABLE><HRALIGN="LEFT"WIDTH="100%"></DIV><DIVCLASS="SECT1"><H1CLASS="SECT1"><ANAME="WRAPPER"></A>33.3. Shell Wrappers</H1><P><ANAME="SHWRAPPER"></A></P><P>A <SPANCLASS="QUOTE">"wrapper"</SPAN> is a shell script that embeds a system command or utility, that saves a set of parameters passed to that command. <ANAME="AEN18594"HREF="#FTN.AEN18594">[1]</A> Wrapping a script around a complex command line simplifies invoking it. This is expecially useful with <AHREF="sedawk.html#SEDREF">sed</A> and <AHREF="awk.html#AWKREF">awk</A>.</P><P>A <BCLASS="COMMAND"> sed</B> or <BCLASS="COMMAND"> awk</B> script would normally be invoked from the command line by a <TTCLASS="USERINPUT"><B>sed -e <TTCLASS="REPLACEABLE"><I>'commands'</I></TT></B></TT> or <TTCLASS="USERINPUT"><B>awk <TTCLASS="REPLACEABLE"><I>'commands'</I></TT></B></TT>. Embedding such a script in a Bash script permits calling it more simply, and makes it <SPANCLASS="QUOTE">"reusable"</SPAN>. This also enables combining the functionality of <BCLASS="COMMAND">sed</B> and <BCLASS="COMMAND">awk</B>, for example <AHREF="special-chars.html#PIPEREF">piping</A> the output of a set of <BCLASS="COMMAND">sed</B> commands to <BCLASS="COMMAND">awk</B>. As a saved executable file, you can then repeatedly invoke it in its original form or modified, without the inconvenience of retyping it on the command line.</P><DIVCLASS="EXAMPLE"><HR><ANAME="EX3"></A><P><B>Example 33-1. <ICLASS="FIRSTTERM">shell wrapper</I></B></P><TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="100%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 #!/bin/bash 2 3 # This is a simple script that removes blank lines from a file. 4 # No argument checking. 5 # 6 # You might wish to add something like: 7 # 8 # E_NOARGS=65 9 # if [ -z "$1" ] 10 # then 11 # echo "Usage: `basename $0` target-file" 12 # exit $E_NOARGS 13 # fi 14 15 16 # Same as 17 # sed -e '/^$/d' filename 18 # invoked from the command line. 19 20 sed -e /^$/d "$1" 21 # The '-e' means an "editing" command follows (optional here). 22 # '^' is the beginning of line, '$' is the end. 23 # This match lines with nothing between the beginning and the end, 24 #+ blank lines. 25 # The 'd' is the delete command. 26 27 # Quoting the command-line arg permits 28 #+ whitespace and special characters in the filename. 29 30 # Note that this script doesn't actually change the target file. 31 # If you need to do that, redirect its output. 32 33 exit 0</PRE></TD></TR></TABLE><HR></DIV><DIVCLASS="EXAMPLE"><HR><ANAME="EX4"></A><P><B>Example 33-2. A slightly more complex <ICLASS="FIRSTTERM">shell wrapper</I></B></P><TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="100%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 #!/bin/bash 2 3 # "subst", a script that substitutes one pattern for 4 #+ another in a file, 5 #+ i.e., "subst Smith Jones letter.txt". 6 7 ARGS=3 # Script requires 3 arguments. 8 E_BADARGS=65 # Wrong number of arguments passed to script. 9 10 if [ $# -ne "$ARGS" ] 11 # Test number of arguments to script (always a good idea). 12 then 13 echo "Usage: `basename $0` old-pattern new-pattern filename" 14 exit $E_BADARGS 15 fi 16 17 old_pattern=$1 18 new_pattern=$2 19 20 if [ -f "$3" ] 21 then 22 file_name=$3 23 else 24 echo "File \"$3\" does not exist." 25 exit $E_BADARGS 26 fi 27 28 29 # Here is where the heavy work gets done. 30 31 # ----------------------------------------------- 32 sed -e "s/$old_pattern/$new_pattern/g" $file_name 33 # ----------------------------------------------- 34 35 # 's' is, of course, the substitute command in sed, 36 #+ and /pattern/ invokes address matching. 37 # The "g", or global flag causes substitution for *every* 38 #+ occurence of $old_pattern on each line, not just the first. 39 # Read the literature on 'sed' for an in-depth explanation. 40 41 exit 0 # Successful invocation of the script returns 0.</PRE></TD></TR></TABLE><HR></DIV><DIVCLASS="EXAMPLE"><HR><ANAME="LOGGINGWRAPPER"></A><P><B>Example 33-3. A generic <ICLASS="FIRSTTERM">shell wrapper</I> that writes to a logfile</B></P><TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="100%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 #!/bin/bash 2 # Generic shell wrapper that performs an operation 3 #+ and logs it. 4 5 # Must set the following two variables. 6 OPERATION= 7 # Can be a complex chain of commands, 8 #+ for example an awk script or a pipe . . . 9 LOGFILE= 10 # Command-line arguments, if any, for the operation. 11 12 13 OPTIONS="$@" 14 15 16 # Log it. 17 echo "`date` + `whoami` + $OPERATION "$@"" >> $LOGFILE 18 # Now, do it. 19 exec $OPERATION "$@" 20 21 # It's necessary to do the logging before the operation. 22 # Why?</PRE></TD></TR></TABLE><HR></DIV><DIVCLASS="EXAMPLE"><HR><ANAME="PRASC"></A><P><B>Example 33-4. A <ICLASS="FIRSTTERM">shell wrapper</I> around an awk script</B></P><TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="100%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 #!/bin/bash 2 # pr-ascii.sh: Prints a table of ASCII characters. 3 4 START=33 # Range of printable ASCII characters (decimal). 5 END=125 6 7 echo " Decimal Hex Character" # Header. 8 echo " ------- --- ---------" 9 10 for ((i=START; i<=END; i++)) 11 do 12 echo $i | awk '{printf(" %3d %2x %c\n", $1, $1, $1)}' 13 # The Bash printf builtin will not work in this context: 14 # printf "%c" "$i" 15 done 16 17 exit 0 18 19 20 # Decimal Hex Character 21 # ------- --- --------- 22 # 33 21 ! 23 # 34 22 " 24 # 35 23 # 25 # 36 24 $ 26 # 27 # . . . 28 # 29 # 122 7a z 30 # 123 7b { 31 # 124 7c | 32 # 125 7d } 33 34 35 # Redirect the output of this script to a file 36 #+ or pipe it to "more": sh pr-asc.sh | more</PRE></TD></TR></TABLE><HR></DIV><DIVCLASS="EXAMPLE"><HR><ANAME="COLTOTALER"></A><P><B>Example 33-5. A <ICLASS="FIRSTTERM">shell wrapper</I> around another awk script</B></P><TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="100%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 #!/bin/bash 2 3 # Adds up a specified column (of numbers) in the target file. 4 5 ARGS=2 6 E_WRONGARGS=65 7 8 if [ $# -ne "$ARGS" ] # Check for proper no. of command line args. 9 then 10 echo "Usage: `basename $0` filename column-number" 11 exit $E_WRONGARGS 12 fi 13 14 filename=$1 15 column_number=$2 16 17 # Passing shell variables to the awk part of the script is a bit tricky. 18 # One method is to strong-quote the Bash-script variable 19 #+ within the awk script. 20 # $'$BASH_SCRIPT_VAR' 21 # ^ ^ 22 # This is done in the embedded awk script below. 23 # See the awk documentation for more details. 24 25 # A multi-line awk script is invoked by: awk ' ..... ' 26 27 28 # Begin awk script. 29 # ----------------------------- 30 awk ' 31 32 { total += $'"${column_number}"' 33 } 34 END { 35 print total 36 } 37 38 ' "$filename" 39 # ----------------------------- 40 # End awk script. 41 42 43 # It may not be safe to pass shell variables to an embedded awk script, 44 #+ so Stephane Chazelas proposes the following alternative: 45 # --------------------------------------- 46 # awk -v column_number="$column_number" ' 47 # { total += $column_number 48 # } 49 # END { 50 # print total 51 # }' "$filename" 52 # --------------------------------------- 53 54 55 exit 0</PRE></TD></TR></TABLE><HR></DIV><P><ANAME="PERLREF"></A>For those scripts needing a single do-it-all tool, a Swiss army knife, there is <ICLASS="FIRSTTERM">Perl</I>. Perl combines the capabilities of <BCLASS="COMMAND">sed</B> and <BCLASS="COMMAND">awk</B>, and throws in a large subset of <ICLASS="FIRSTTERM">C</I>, to boot. It is modular and contains support for everything ranging from object-oriented programming up to and including the kitchen sink. Short Perl scripts lend themselves to embedding in shell scripts, and there may even be some substance to the claim that Perl can totally replace shell scripting (though the author of this document remains skeptical).</P><P><ANAME="PERLEMB"></A></P><DIVCLASS="EXAMPLE"><HR><ANAME="EX56"></A><P><B>Example 33-6. Perl embedded in a <ICLASS="FIRSTTERM">Bash</I> script</B></P><TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="100%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 #!/bin/bash 2 3 # Shell commands may precede the Perl script. 4 echo "This precedes the embedded Perl script within \"$0\"." 5 echo "===============================================================" 6 7 perl -e 'print "This is an embedded Perl script.\n";' 8 # Like sed, Perl also uses the "-e" option. 9 10 echo "===============================================================" 11 echo "However, the script may also contain shell and system commands." 12 13 exit 0</PRE></TD></TR></TABLE><HR></DIV><P>It is even possible to combine a Bash script and Perl script within the same file. Depending on how the script is invoked, either the Bash part or the Perl part will execute.</P><P><ANAME="BASHANDPERL0"></A></P><DIVCLASS="EXAMPLE"><HR><ANAME="BASHANDPERL"></A><P><B>Example 33-7. Bash and Perl scripts combined</B></P><TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="100%"><TR><TD><PRECLASS="PROGRAMLISTING"> 1 #!/bin/bash 2 # bashandperl.sh 3 4 echo "Greetings from the Bash part of the script." 5 # More Bash commands may follow here. 6 7 exit 0 8 # End of Bash part of the script. 9 10 # ======================================================= 11 12 #!/usr/bin/perl 13 # This part of the script must be invoked with -x option. 14 15 print "Greetings from the Perl part of the script.\n"; 16 # More Perl commands may follow here. 17 18 # End of Perl part of the script.</PRE></TD></TR></TABLE><HR></DIV><P> <TABLEBORDER="0"BGCOLOR="#E0E0E0"WIDTH="100%"><TR><TD><PRECLASS="SCREEN"> <TTCLASS="PROMPT">bash$ </TT><TTCLASS="USERINPUT"><B>bash bashandperl.sh</B></TT> <TTCLASS="COMPUTEROUTPUT">Greetings from the Bash part of the script.</TT> <TTCLASS="PROMPT">bash$ </TT><TTCLASS="USERINPUT"><B>perl -x bashandperl.sh</B></TT> <TTCLASS="COMPUTEROUTPUT">Greetings from the Perl part of the script.</TT> </PRE></TD></TR></TABLE> </P></DIV><H3CLASS="FOOTNOTES">Notes</H3><TABLEBORDER="0"CLASS="FOOTNOTES"WIDTH="100%"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="5%"><ANAME="FTN.AEN18594"HREF="wrapper.html#AEN18594">[1]</A></TD><TDALIGN="LEFT"VALIGN="TOP"WIDTH="95%"><P>Quite a number of Linux utilities are, in fact, shell wrappers. Some examples are <TTCLASS="FILENAME">/usr/bin/pdf2ps</TT>, <TTCLASS="FILENAME">/usr/bin/batch</TT>, and <TTCLASS="FILENAME">/usr/X11R6/bin/xmkmf</TT>.</P></TD></TR></TABLE><DIVCLASS="NAVFOOTER"><HRALIGN="LEFT"WIDTH="100%"><TABLESUMMARY="Footer navigation table"WIDTH="100%"BORDER="0"CELLPADDING="0"CELLSPACING="0"><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top"><AHREF="opprecedence.html"ACCESSKEY="P">Prev</A></TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="index.html"ACCESSKEY="H">Home</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top"><AHREF="testsandcomparisons.html"ACCESSKEY="N">Next</A></TD></TR><TR><TDWIDTH="33%"ALIGN="left"VALIGN="top">Operator Precedence</TD><TDWIDTH="34%"ALIGN="center"VALIGN="top"><AHREF="miscellany.html"ACCESSKEY="U">Up</A></TD><TDWIDTH="33%"ALIGN="right"VALIGN="top">Tests and Comparisons: Alternatives</TD></TR></TABLE></DIV></BODY></HTML>⌨️ 快捷键说明
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