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 38 
 39 case "$answer" in
 40 [yY]) rm -f $OF
 41       echo "$OF erased."
 42       ;;
 43 *)    echo "$OF not erased.";;
 44 esac
 45 
 46 echo
 47 
 48 # Exercise:
 49 # Change the above "case" statement to also accept "yes" and "Yes" as input.
 50 
 51&nbsp;exit 0</PRE
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><DIV
CLASS="EXAMPLE"
><HR><A
NAME="COLLATZ"
></A
><P
><B
>例子 A-6. Collatz序列</B
></P
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BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
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><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>  1&nbsp;#!/bin/bash
  2&nbsp;# collatz.sh
  3&nbsp;
  4&nbsp;#  The notorious "hailstone" or Collatz series.
  5&nbsp;#  -------------------------------------------
  6&nbsp;#  1) Get the integer "seed" from the command line.
  7&nbsp;#  2) NUMBER &#60;--- seed
  8&nbsp;#  3) Print NUMBER.
  9&nbsp;#  4)  If NUMBER is even, divide by 2, or
 10&nbsp;#  5)+ if odd, multiply by 3 and add 1.
 11&nbsp;#  6) NUMBER &#60;--- result 
 12&nbsp;#  7) Loop back to step 3 (for specified number of iterations).
 13&nbsp;#
 14&nbsp;#  The theory is that every sequence,
 15&nbsp;#+ no matter how large the initial value,
 16&nbsp;#+ eventually settles down to repeating "4,2,1..." cycles,
 17&nbsp;#+ even after fluctuating through a wide range of values.
 18&nbsp;#
 19&nbsp;#  This is an instance of an "iterate",
 20&nbsp;#+ an operation that feeds its output back into the input.
 21&nbsp;#  Sometimes the result is a "chaotic" series.
 22&nbsp;
 23&nbsp;
 24&nbsp;MAX_ITERATIONS=200
 25&nbsp;# For large seed numbers (&#62;32000), increase MAX_ITERATIONS.
 26&nbsp;
 27&nbsp;h=${1:-$$}                      #  Seed
 28&nbsp;                                #  Use $PID as seed,
 29&nbsp;                                #+ if not specified as command-line arg.
 30&nbsp;
 31&nbsp;echo
 32&nbsp;echo "C($h) --- $MAX_ITERATIONS Iterations"
 33&nbsp;echo
 34&nbsp;
 35&nbsp;for ((i=1; i&#60;=MAX_ITERATIONS; i++))
 36&nbsp;do
 37&nbsp;
 38&nbsp;echo -n "$h	"
 39&nbsp;#          ^^^^^
 40&nbsp;#           tab
 41&nbsp;
 42&nbsp;  let "remainder = h % 2"
 43&nbsp;  if [ "$remainder" -eq 0 ]   # Even?
 44&nbsp;  then
 45&nbsp;    let "h /= 2"              # Divide by 2.
 46&nbsp;  else
 47&nbsp;    let "h = h*3 + 1"         # Multiply by 3 and add 1.
 48&nbsp;  fi
 49&nbsp;
 50&nbsp;
 51&nbsp;COLUMNS=10                    # Output 10 values per line.
 52&nbsp;let "line_break = i % $COLUMNS"
 53&nbsp;if [ "$line_break" -eq 0 ]
 54&nbsp;then
 55&nbsp;  echo
 56&nbsp;fi  
 57&nbsp;
 58&nbsp;done
 59&nbsp;
 60&nbsp;echo
 61&nbsp;
 62&nbsp;#  For more information on this mathematical function,
 63&nbsp;#+ see "Computers, Pattern, Chaos, and Beauty", by Pickover, p. 185 ff.,
 64&nbsp;#+ as listed in the bibliography.
 65&nbsp;
 66&nbsp;exit 0</PRE
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><DIV
CLASS="EXAMPLE"
><HR><A
NAME="DAYSBETWEEN"
></A
><P
><B
>例子 A-7. <B
CLASS="COMMAND"
>days-between</B
>: 计算两个日期之间天数差</B
></P
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BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
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><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>  1&nbsp;#!/bin/bash
  2&nbsp;# days-between.sh:    Number of days between two dates.
  3&nbsp;# Usage: ./days-between.sh [M]M/[D]D/YYYY [M]M/[D]D/YYYY
  4&nbsp;#
  5&nbsp;# Note: Script modified to account for changes in Bash 2.05b
  6&nbsp;#+      that closed the loophole permitting large negative
  7&nbsp;#+      integer return values.
  8&nbsp;
  9&nbsp;ARGS=2                # Two command line parameters expected.
 10&nbsp;E_PARAM_ERR=65        # Param error.
 11&nbsp;
 12&nbsp;REFYR=1600            # Reference year.
 13&nbsp;CENTURY=100
 14&nbsp;DIY=365
 15&nbsp;ADJ_DIY=367           # Adjusted for leap year + fraction.
 16&nbsp;MIY=12
 17&nbsp;DIM=31
 18&nbsp;LEAPCYCLE=4
 19&nbsp;
 20&nbsp;MAXRETVAL=255         #  Largest permissable
 21&nbsp;                      #+ positive return value from a function.
 22&nbsp;
 23&nbsp;diff=                 # Declare global variable for date difference.
 24&nbsp;value=                # Declare global variable for absolute value.
 25&nbsp;day=                  # Declare globals for day, month, year.
 26&nbsp;month=
 27&nbsp;year=
 28&nbsp;
 29&nbsp;
 30&nbsp;Param_Error ()        # Command line parameters wrong.
 31&nbsp;{
 32&nbsp;  echo "Usage: `basename $0` [M]M/[D]D/YYYY [M]M/[D]D/YYYY"
 33&nbsp;  echo "       (date must be after 1/3/1600)"
 34&nbsp;  exit $E_PARAM_ERR
 35&nbsp;}  
 36&nbsp;
 37&nbsp;
 38&nbsp;Parse_Date ()                 # Parse date from command line params.
 39&nbsp;{
 40&nbsp;  month=${1%%/**}
 41&nbsp;  dm=${1%/**}                 # Day and month.
 42&nbsp;  day=${dm#*/}
 43&nbsp;  let "year = `basename $1`"  # Not a filename, but works just the same.
 44&nbsp;}  
 45&nbsp;
 46&nbsp;
 47&nbsp;check_date ()                 # Checks for invalid date(s) passed.
 48&nbsp;{
 49&nbsp;  [ "$day" -gt "$DIM" ] || [ "$month" -gt "$MIY" ] || [ "$year" -lt "$REFYR" ] &#38;&#38; Param_Error
 50&nbsp;  # Exit script on bad value(s).
 51&nbsp;  # Uses "or-list / and-list".
 52&nbsp;  #
 53&nbsp;  # Exercise: Implement more rigorous date checking.
 54&nbsp;}
 55&nbsp;
 56&nbsp;
 57&nbsp;strip_leading_zero () #  Better to strip possible leading zero(s)
 58&nbsp;{                     #+ from day and/or month
 59&nbsp;  return ${1#0}       #+ since otherwise Bash will interpret them
 60&nbsp;}                     #+ as octal values (POSIX.2, sect 2.9.2.1).
 61&nbsp;
 62&nbsp;
 63&nbsp;day_index ()          # Gauss' Formula:
 64&nbsp;{                     # Days from Jan. 3, 1600 to date passed as param.
 65&nbsp;
 66&nbsp;  day=$1
 67&nbsp;  month=$2
 68&nbsp;  year=$3
 69&nbsp;
 70&nbsp;  let "month = $month - 2"
 71&nbsp;  if [ "$month" -le 0 ]
 72&nbsp;  then
 73&nbsp;    let "month += 12"
 74&nbsp;    let "year -= 1"
 75&nbsp;  fi  
 76&nbsp;
 77&nbsp;  let "year -= $REFYR"
 78&nbsp;  let "indexyr = $year / $CENTURY"
 79&nbsp;
 80&nbsp;
 81&nbsp;  let "Days = $DIY*$year + $year/$LEAPCYCLE - $indexyr + $indexyr/$LEAPCYCLE + $ADJ_DIY*$month/$MIY + $day - $DIM"
 82&nbsp;  #  For an in-depth explanation of this algorithm, see
 83&nbsp;  #+ http://home.t-online.de/home/berndt.schwerdtfeger/cal.htm
 84&nbsp;
 85&nbsp;
 86&nbsp;  echo $Days
 87&nbsp;
 88&nbsp;}  
 89&nbsp;
 90&nbsp;
 91&nbsp;calculate_difference ()            # Difference between to day indices.
 92&nbsp;{
 93&nbsp;  let "diff = $1 - $2"             # Global variable.
 94&nbsp;}  
 95&nbsp;
 96&nbsp;
 97&nbsp;abs ()                             #  Absolute value
 98&nbsp;{                                  #  Uses global "value" variable.
 99&nbsp;  if [ "$1" -lt 0 ]                #  If negative
100&nbsp;  then                             #+ then
101&nbsp;    let "value = 0 - $1"           #+ change sign,
102&nbsp;  else                             #+ else
103&nbsp;    let "value = $1"               #+ leave it alone.
104&nbsp;  fi
105&nbsp;}
106&nbsp;
107&nbsp;
108&nbsp;
109&nbsp;if [ $# -ne "$ARGS" ]              # Require two command line params.
110&nbsp;then
111&nbsp;  Param_Error
112&nbsp;fi  
113&nbsp;
114&nbsp;Parse_Date $1
115&nbsp;check_date $day $month $year       #  See if valid date.
116&nbsp;
117&nbsp;strip_leading_zero $day            #  Remove any leading zeroes
118&nbsp;day=$?                             #+ on day and/or month.
119&nbsp;strip_leading_zero $month
120&nbsp;month=$?
121&nbsp;
122&nbsp;let "date1 = `day_index $day $month $year`"
123&nbsp;
124&nbsp;
125&nbsp;Parse_Date $2
126&nbsp;check_date $day $month $year
127&nbsp;
128&nbsp;strip_leading_zero $day
129&nbsp;day=$?
130&nbsp;strip_leading_zero $month
131&nbsp;month=$?
132&nbsp;
133&nbsp;date2=$(day_index $day $month $year) # Command substitution.
134&nbsp;
135&nbsp;
136&nbsp;calculate_difference $date1 $date2
137&nbsp;
138&nbsp;abs $diff                            # Make sure it's positive.
139&nbsp;diff=$value
140&nbsp;
141&nbsp;echo $diff
142&nbsp;
143&nbsp;exit 0
144&nbsp;#  Compare this script with
145&nbsp;#+ the implementation of Gauss' Formula in a C program at:
146&nbsp;#+    http://buschencrew.hypermart.net/software/datedif</PRE
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><HR></DIV
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="MAKEDICT"
></A
><P
><B
>例子 A-8. 构造一个<SPAN
CLASS="QUOTE"
>"字典"</SPAN
></B
></P
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BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
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COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>  1&nbsp;#!/bin/bash
  2&nbsp;# makedict.sh  [make dictionary]
  3&nbsp;
  4&nbsp;# Modification of /usr/sbin/mkdict script.
  5&nbsp;# Original script copyright 1993, by Alec Muffett.
  6&nbsp;#
  7&nbsp;#  This modified script included in this document in a manner
  8&nbsp;#+ consistent with the "LICENSE" document of the "Crack" package
  9&nbsp;#+ that the original script is a part of.
 10&nbsp;
 11&nbsp;#  This script processes text files to produce a sorted list
 12&nbsp;#+ of words found in the files.
 13&nbsp;#  This may be useful for compiling dictionaries
 14&nbsp;#+ and for lexicographic research.
 15&nbsp;
 16&nbsp;
 17&nbsp;E_BADARGS=65
 18&nbsp;
 19&nbsp;if [ ! -r "$1" ]                     #  Need at least one
 20&nbsp;then                                 #+ valid file argument.
 21&nbsp;  echo "Usage: $0 files-to-process"
 22&nbsp;  exit $E_BADARGS
 23&nbsp;fi  
 24&nbsp;
 25&nbsp;
 26&nbsp;# SORT="sort"                        #  No longer necessary to define options
 27&nbsp;                                     #+ to sort. Changed from original script.
 28&nbsp;
 29&nbsp;cat $* |                             # Contents of specified files to stdout.
 30&nbsp;        tr A-Z a-z |                 # Convert to lowercase.
 31&nbsp;        tr ' ' '\012' |              # New: change spaces to newlines.
 32&nbsp;#       tr -cd '\012[a-z][0-9]' |    #  Get rid of everything non-alphanumeric
 33&nbsp;                                     #+ (original script).
 34&nbsp;        tr -c '\012a-z'  '\012' |    #  Rather than deleting
 35&nbsp;                                     #+ now change non-alpha to newlines.
 36&nbsp;        sort |                       # $SORT options unnecessary now.
 37&nbsp;        uniq |                       # Remove duplicates.
 38&nbsp;        grep -v '^#' |               # Delete lines beginning with a hashmark.
 39&nbsp;        grep -v '^$'                 # Delete blank lines.
 40&nbsp;
 41&nbsp;exit 0	</PRE
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><HR></DIV
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="SOUNDEX"
></A
><P
><B
>例子 A-9. Soundex转换</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="PROGRAMLISTING"
>  1&nbsp;#!/bin/bash
  2&nbsp;# soundex.sh: Calculate "soundex" code for names
  3&nbsp;
  4&nbsp;# =======================================================
  5&nbsp;#        Soundex script
  6&nbsp;#              by
  7&nbsp;#         Mendel Cooper
  8&nbsp;#     [e-mail]
  9&nbsp;#       23 January, 2002
 10&nbsp;#
 11&nbsp;#   Placed in the Public Domain.
 12&nbsp;#
 13&nbsp;# A slightly different version of this script appeared in
 14&nbsp;#+ Ed Schaefer's July, 2002 "Shell Corner" column
 15&nbsp;#+ in "Unix Review" on-line,
 16&nbsp;#+ http://www.unixreview.com/documents/uni1026336632258/
 17&nbsp;# =======================================================
 18&nbsp;
 19&nbsp;
 20&nbsp;ARGCOUNT=1                     # Need name as argument.
 21&nbsp;E_WRONGARGS=70
 22&nbsp;
 23&nbsp;if [ $# -ne "$ARGCOUNT" ]
 24&nbsp;then
 25&nbsp;  echo "Usage: `basename $0` name"
 26&nbsp;  exit $E_WRONGARGS
 27&nbsp;fi  
 28&nbsp;
 29&nbsp;
 30&nbsp;assign_value ()                #  Assigns numerical value
 31&nbsp;{                              #+ to letters of name.
 32&nbsp;
 33&nbsp;  val1=bfpv                    # 'b,f,p,v' = 1
 34&nbsp;  val2=cgjkqsxz                # 'c,g,j,k,q,s,x,z' = 2
 35&nbsp;  val3=dt                      #  etc.
 36&nbsp;  val4=l
 37&nbsp;  val5=mn
 38&nbsp;  val6=r
 39&nbsp;
 40&nbsp;# Exceptionally clever use of 'tr' follows.
 41&nbsp;# Try to figure out what is going on here.
 42&nbsp;
 43&nbsp;value=$( echo "$1" \
 44&nbsp;| tr -d wh \
 45&nbsp;| tr $val1 1 | tr $val2 2 | tr $val3 3 \
 46&nbsp;| tr $val4 4 | tr $val5 5 | tr $val6 6 \
 47&nbsp;| tr -s 123456 \
 48&nbsp;| tr -d aeiouy )
 49&nbsp;
 50&nbsp;# Assign letter values.
 51&nbsp;# Remove duplicate numbers, except when separated by vowels.
 52&nbsp;# Ignore vowels, except as separators, so delete them last.
 53&nbsp;# Ignore 'w' and 'h', even as separators, so delete them first.
 54&nbsp;#
 55&nbsp;# The above command substitution lays more pipe than a plumber &#60;g&#62;.
 56&nbsp;
 57&nbsp;}  
 58&nbsp;
 59&nbsp;
 60&nbsp;input_name="$1"