Bash 脚本高级编程指南
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36.2. Shell 包装器

一个 包装器 是一个 shell 脚本，它嵌入一个系统命令或实用程序，接受并将一组参数传递给该命令。 [1] 将脚本包装在复杂的命令行周围简化了调用它。 这对于 sed 和 awk 尤其有用。

一个 sed 或 awk 脚本通常通过以下方式从命令行调用：sed -e'commands'或awk'commands'。 将这样的脚本嵌入到 Bash 脚本中可以更简单地调用它，并使其 可重用。 这也使得能够结合 sed 和 awk 的功能，例如将一组 sed 命令的输出 管道传输 到 awk。 作为已保存的可执行文件，您可以重复地以其原始形式或修改后的形式调用它，而无需在命令行中重新键入它的不便。

示例 36-1. shell 包装器

#!/bin/bash

# This simple script removes blank lines from a file.
# No argument checking.
#
# You might wish to add something like:
#
# E_NOARGS=85
# if [ -z "$1" ]
# then
#  echo "Usage: `basename $0` target-file"
#  exit $E_NOARGS
# fi



sed -e /^$/d "$1"
# Same as
#    sed -e '/^$/d' filename
# invoked from the command-line.

#  The '-e' means an "editing" command follows (optional here).
#  '^' indicates the beginning of line, '$' the end.
#  This matches lines with nothing between the beginning and the end --
#+ blank lines.
#  The 'd' is the delete command.

#  Quoting the command-line arg permits
#+ whitespace and special characters in the filename.

#  Note that this script doesn't actually change the target file.
#  If you need to do that, redirect its output.

exit

示例 36-2. 一个稍微复杂的 shell 包装器

#!/bin/bash

#  subst.sh: a script that substitutes one pattern for
#+ another in a file,
#+ i.e., "sh subst.sh Smith Jones letter.txt".
#                     Jones replaces Smith.

ARGS=3         # Script requires 3 arguments.
E_BADARGS=85   # Wrong number of arguments passed to script.

if [ $# -ne "$ARGS" ]
then
  echo "Usage: `basename $0` old-pattern new-pattern filename"
  exit $E_BADARGS
fi

old_pattern=$1
new_pattern=$2

if [ -f "$3" ]
then
    file_name=$3
else
    echo "File \"$3\" does not exist."
    exit $E_BADARGS
fi


# -----------------------------------------------
#  Here is where the heavy work gets done.
sed -e "s/$old_pattern/$new_pattern/g" $file_name
# -----------------------------------------------

#  's' is, of course, the substitute command in sed,
#+ and /pattern/ invokes address matching.
#  The 'g,' or global flag causes substitution for EVERY
#+ occurence of $old_pattern on each line, not just the first.
#  Read the 'sed' docs for an in-depth explanation.

exit $?  # Redirect the output of this script to write to a file.

示例 36-3. 一个通用的 shell 包装器，它写入日志文件

#!/bin/bash
#  logging-wrapper.sh
#  Generic shell wrapper that performs an operation
#+ and logs it.

DEFAULT_LOGFILE=logfile.txt

# Set the following two variables.
OPERATION=
#         Can be a complex chain of commands,
#+        for example an awk script or a pipe . . .

LOGFILE=
if [ -z "$LOGFILE" ]
then     # If not set, default to ...
  LOGFILE="$DEFAULT_LOGFILE"
fi

#         Command-line arguments, if any, for the operation.
OPTIONS="$@"


# Log it.
echo "`date` + `whoami` + $OPERATION "$@"" >> $LOGFILE
# Now, do it.
exec $OPERATION "$@"

# It's necessary to do the logging before the operation.
# Why?

示例 36-4. 一个围绕 awk 脚本的 shell 包装器

#!/bin/bash
# pr-ascii.sh: Prints a table of ASCII characters.

START=33   # Range of printable ASCII characters (decimal).
END=127    # Will not work for unprintable characters (> 127).

echo " Decimal   Hex     Character"   # Header.
echo " -------   ---     ---------"

for ((i=START; i<=END; i++))
do
  echo $i | awk '{printf("  %3d       %2x         %c\n", $1, $1, $1)}'
# The Bash printf builtin will not work in this context:
#     printf "%c" "$i"
done

exit 0


#  Decimal   Hex     Character
#  -------   ---     ---------
#    33       21         !
#    34       22         "
#    35       23         #
#    36       24         $
#
#    . . .
#
#   122       7a         z
#   123       7b         {
#   124       7c         |
#   125       7d         }


#  Redirect the output of this script to a file
#+ or pipe it to "more":  sh pr-asc.sh | more

示例 36-5. 一个围绕另一个 awk 脚本的 shell 包装器

#!/bin/bash

# Adds up a specified column (of numbers) in the target file.
# Floating-point (decimal) numbers okay, because awk can handle them.

ARGS=2
E_WRONGARGS=85

if [ $# -ne "$ARGS" ] # Check for proper number of command-line args.
then
   echo "Usage: `basename $0` filename column-number"
   exit $E_WRONGARGS
fi

filename=$1
column_number=$2

#  Passing shell variables to the awk part of the script is a bit tricky.
#  One method is to strong-quote the Bash-script variable
#+ within the awk script.
#     $'$BASH_SCRIPT_VAR'
#      ^                ^
#  This is done in the embedded awk script below.
#  See the awk documentation for more details.

# A multi-line awk script is here invoked by
#   awk '
#   ...
#   ...
#   ...
#   '


# Begin awk script.
# -----------------------------
awk '

{ total += $'"${column_number}"'
}
END {
     print total
}     

' "$filename"
# -----------------------------
# End awk script.


#   It may not be safe to pass shell variables to an embedded awk script,
#+  so Stephane Chazelas proposes the following alternative:
#   ---------------------------------------
#   awk -v column_number="$column_number" '
#   { total += $column_number
#   }
#   END {
#       print total
#   }' "$filename"
#   ---------------------------------------


exit 0

对于那些需要一个多功能工具（瑞士军刀）的脚本来说，有 Perl。 Perl 结合了 sed 和 awk 的功能，并加入了 C 的一个大型子集。 它是模块化的，并包含从面向对象编程到应有尽有的一切支持。 短小的 Perl 脚本适合嵌入到 shell 脚本中，并且 Perl 可以完全取代 shell 脚本的说法可能有一些道理（尽管《ABS 指南》的作者仍然持怀疑态度）。

示例 36-6. 嵌入在 Bash 脚本中的 Perl

#!/bin/bash

# Shell commands may precede the Perl script.
echo "This precedes the embedded Perl script within \"$0\"."
echo "==============================================================="

perl -e 'print "This line prints from an embedded Perl script.\n";'
# Like sed, Perl also uses the "-e" option.

echo "==============================================================="
echo "However, the script may also contain shell and system commands."

exit 0

甚至可以将 Bash 脚本和 Perl 脚本组合在同一个文件中。 根据脚本的调用方式，Bash 部分或 Perl 部分将执行。

示例 36-7. Bash 和 Perl 脚本的组合

#!/bin/bash
# bashandperl.sh

echo "Greetings from the Bash part of the script, $0."
# More Bash commands may follow here.

exit
# End of Bash part of the script.

# =======================================================

#!/usr/bin/perl
# This part of the script must be invoked with
#    perl -x bashandperl.sh

print "Greetings from the Perl part of the script, $0.\n";
#      Perl doesn't seem to like "echo" ...
# More Perl commands may follow here.

# End of Perl part of the script.

bash$ bash bashandperl.sh
Greetings from the Bash part of the script.


bash$ perl -x bashandperl.sh
Greetings from the Perl part of the script.

当然，也可以在 shell 包装器中嵌入更具异国情调的脚本语言。 例如，Python ...

示例 36-8. 嵌入在 Bash 脚本中的 Python

#!/bin/bash
# ex56py.sh

# Shell commands may precede the Python script.
echo "This precedes the embedded Python script within \"$0.\""
echo "==============================================================="

python -c 'print "This line prints from an embedded Python script.\n";'
# Unlike sed and perl, Python uses the "-c" option.
python -c 'k = raw_input( "Hit a key to exit to outer script. " )'

echo "==============================================================="
echo "However, the script may also contain shell and system commands."

exit 0

将脚本包装在 mplayer 和 Google 的翻译服务器周围，您可以创建可以与您对话的东西。

示例 36-9. 一个会说话的脚本

#!/bin/bash
#   Courtesy of:
#   http://elinux.org/RPi_Text_to_Speech_(Speech_Synthesis)

#  You must be on-line for this script to work,
#+ so you can access the Google translation server.
#  Of course, mplayer must be present on your computer.

speak()
  {
  local IFS=+
  # Invoke mplayer, then connect to Google translation server.
  /usr/bin/mplayer -ao alsa -really-quiet -noconsolecontrols \
 "http://translate.google.com/translate_tts?tl=en&q="$*""
  # Google translates, but can also speak.
  }

LINES=4

spk=$(tail -$LINES $0) # Tail end of same script!
speak "$spk"
exit
# Browns. Nice talking to you.

一个关于复杂 shell 包装器的有趣例子是 Martin Matusiak 的 undvd 脚本，它为复杂的 mencoder 实用程序提供了一个易于使用的命令行界面。 另一个例子是 Itzchak Rehberg 的 Ext3Undel，这是一组用于恢复 ext3 文件系统上已删除文件的脚本。

注释

[1]

实际上，相当多的 Linux 实用程序是 shell 包装器。 一些例子是：/usr/bin/pdf2ps, /usr/bin/batch，以及/usr/bin/xmkmf.

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