arrays.html

Shall高级编程

  17                         # All elements.
  18 
  19 echo ${arrayZ[@]:1}     # two three four five five
  20                         # All elements following element[0].
  21 
  22 echo ${arrayZ[@]:1:2}   # two three
  23                         # Only the two elements after element[0].
  24 
  25 echo "-----------------------"
  26 
  27 #  Substring Removal
  28 #  Removes shortest match from front of string(s),
  29 #+ where the substring is a regular expression.
  30 
  31 echo ${arrayZ[@]#f*r}   # one two three five five
  32                         # Applied to all elements of the array.
  33                         # Matches "four" and removes it.
  34 
  35 # Longest match from front of string(s)
  36 echo ${arrayZ[@]##t*e}  # one two four five five
  37                         # Applied to all elements of the array.
  38                         # Matches "three" and removes it.
  39 
  40 # Shortest match from back of string(s)
  41 echo ${arrayZ[@]%h*e}   # one two t four five five
  42                         # Applied to all elements of the array.
  43                         # Matches "hree" and removes it.
  44 
  45 # Longest match from back of string(s)
  46 echo ${arrayZ[@]%%t*e}  # one two four five five
  47                         # Applied to all elements of the array.
  48                         # Matches "three" and removes it.
  49 
  50 echo "-----------------------"
  51 
  52 # Substring Replacement
  53 
  54 # Replace first occurance of substring with replacement
  55 echo ${arrayZ[@]/fiv/XYZ}   # one two three four XYZe XYZe
  56                             # Applied to all elements of the array.
  57 
  58 # Replace all occurances of substring
  59 echo ${arrayZ[@]//iv/YY}    # one two three four fYYe fYYe
  60                             # Applied to all elements of the array.
  61 
  62 # Delete all occurances of substring
  63 # Not specifing a replacement means 'delete'
  64 echo ${arrayZ[@]//fi/}      # one two three four ve ve
  65                             # Applied to all elements of the array.
  66 
  67 # Replace front-end occurances of substring
  68 echo ${arrayZ[@]/#fi/XY}    # one two three four XYve XYve
  69                             # Applied to all elements of the array.
  70 
  71 # Replace back-end occurances of substring
  72 echo ${arrayZ[@]/%ve/ZZ}    # one two three four fiZZ fiZZ
  73                             # Applied to all elements of the array.
  74 
  75 echo ${arrayZ[@]/%o/XX}     # one twXX three four five five
  76                             # Why?
  77 
  78 echo "-----------------------"
  79 
  80 
  81 # Before reaching for awk (or anything else) --
  82 # Recall:
  83 #   $( ... ) is command substitution.
  84 #   Functions run as a sub-process.
  85 #   Functions write their output to stdout.
  86 #   Assignment reads the function's stdout.
  87 #   The name[@] notation specifies a "for-each" operation.
  88 
  89 newstr() {
  90     echo -n "!!!"
  91 }
  92 
  93 echo ${arrayZ[@]/%e/$(newstr)}
  94 # on!!! two thre!!! four fiv!!! fiv!!!
  95 # Q.E.D: The replacement action is an 'assignment.'
  96 
  97 #  Accessing the "For-Each"
  98 echo ${arrayZ[@]//*/$(newstr optional_arguments)}
  99 #  Now, if Bash would just pass the matched string as $0
 100 #+ to the function being called . . .
 101 
 102 echo
 103 
 104&nbsp;exit 0</PRE
></TD
></TR
></TABLE
><HR></DIV
><P
><A
HREF="commandsub.html#COMMANDSUBREF"
>Command substitution</A
> can
        construct the individual elements of an array.</P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="SCRIPTARRAY"
></A
><P
><B
>Example 26-5. Loading the contents of a script into an array</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# script-array.sh: Loads this script into an array.
   3&nbsp;# Inspired by an e-mail from Chris Martin (thanks!).
   4&nbsp;
   5&nbsp;script_contents=( $(cat "$0") )  #  Stores contents of this script ($0)
   6&nbsp;                                 #+ in an array.
   7&nbsp;
   8&nbsp;for element in $(seq 0 $((${#script_contents[@]} - 1)))
   9&nbsp;  do                #  ${#script_contents[@]}
  10&nbsp;                    #+ gives number of elements in the array.
  11&nbsp;                    #
  12&nbsp;                    #  Question:
  13&nbsp;                    #  Why is  seq 0  necessary?
  14&nbsp;                    #  Try changing it to seq 1.
  15&nbsp;  echo -n "${script_contents[$element]}"
  16&nbsp;                    # List each field of this script on a single line.
  17&nbsp;  echo -n " -- "    # Use " -- " as a field separator.
  18&nbsp;done
  19&nbsp;
  20&nbsp;echo
  21&nbsp;
  22&nbsp;exit 0
  23&nbsp;
  24&nbsp;# Exercise:
  25&nbsp;# --------
  26&nbsp;#  Modify this script so it lists itself
  27&nbsp;#+ in its original format,
  28&nbsp;#+ complete with whitespace, line breaks, etc.</PRE
></TD
></TR
></TABLE
><HR></DIV
><P
>In an array context, some Bash <A
HREF="internal.html#BUILTINREF"
>builtins</A
> have a slightly
	altered meaning. <A
NAME="ARRAYUNSET"
></A
>For example, <A
HREF="internal.html#UNSETREF"
>unset</A
> deletes array elements, or even
	an entire array.</P
><P
><A
NAME="ARRAYSPECIALPROPS"
></A
></P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="EX67"
></A
><P
><B
>Example 26-6. Some special properties of arrays</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;
   3&nbsp;declare -a colors
   4&nbsp;#  All subsequent commands in this script will treat
   5&nbsp;#+ the variable "colors" as an array.
   6&nbsp;
   7&nbsp;echo "Enter your favorite colors (separated from each other by a space)."
   8&nbsp;
   9&nbsp;read -a colors    # Enter at least 3 colors to demonstrate features below.
  10&nbsp;#  Special option to 'read' command,
  11&nbsp;#+ allowing assignment of elements in an array.
  12&nbsp;
  13&nbsp;echo
  14&nbsp;
  15&nbsp;element_count=${#colors[@]}
  16&nbsp;# Special syntax to extract number of elements in array.
  17&nbsp;#     element_count=${#colors[*]} works also.
  18&nbsp;#
  19&nbsp;#  The "@" variable allows word splitting within quotes
  20&nbsp;#+ (extracts variables separated by whitespace).
  21&nbsp;#
  22&nbsp;#  This corresponds to the behavior of "$@" and "$*"
  23&nbsp;#+ in positional parameters. 
  24&nbsp;
  25&nbsp;index=0
  26&nbsp;
  27&nbsp;while [ "$index" -lt "$element_count" ]
  28&nbsp;do    # List all the elements in the array.
  29&nbsp;  echo ${colors[$index]}
  30&nbsp;  let "index = $index + 1"
  31&nbsp;  # Or:
  32&nbsp;  #    index+=1
  33&nbsp;  # if running Bash, version 3.1 or later.
  34&nbsp;done
  35&nbsp;# Each array element listed on a separate line.
  36&nbsp;# If this is not desired, use  echo -n "${colors[$index]} "
  37&nbsp;#
  38&nbsp;# Doing it with a "for" loop instead:
  39&nbsp;#   for i in "${colors[@]}"
  40&nbsp;#   do
  41&nbsp;#     echo "$i"
  42&nbsp;#   done
  43&nbsp;# (Thanks, S.C.)
  44&nbsp;
  45&nbsp;echo
  46&nbsp;
  47&nbsp;# Again, list all the elements in the array, but using a more elegant method.
  48&nbsp;  echo ${colors[@]}          # echo ${colors[*]} also works.
  49&nbsp;
  50&nbsp;echo
  51&nbsp;
  52&nbsp;# The "unset" command deletes elements of an array, or entire array.
  53&nbsp;unset colors[1]              # Remove 2nd element of array.
  54&nbsp;                             # Same effect as   colors[1]=
  55&nbsp;echo  ${colors[@]}           # List array again, missing 2nd element.
  56&nbsp;
  57&nbsp;unset colors                 # Delete entire array.
  58&nbsp;                             #  unset colors[*] and
  59&nbsp;                             #+ unset colors[@] also work.
  60&nbsp;echo; echo -n "Colors gone."			   
  61&nbsp;echo ${colors[@]}            # List array again, now empty.
  62&nbsp;
  63&nbsp;exit 0</PRE
></TD
></TR
></TABLE
><HR></DIV
><P
><A
NAME="ARRAYNUMELEMENTS"
></A
></P
><P
>As seen in the previous example, either
	<B
CLASS="COMMAND"
>${array_name[@]}</B
> or
	<B
CLASS="COMMAND"
>${array_name[*]}</B
> refers to
	<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>all</I
></SPAN
> the elements of the array.
	Similarly, to get a count of the number of elements in an
	array, use either <B
CLASS="COMMAND"
>${#array_name[@]}</B
>
	or <B
CLASS="COMMAND"
>${#array_name[*]}</B
>.
	<B
CLASS="COMMAND"
>${#array_name}</B
> is the length (number of
	characters) of <B
CLASS="COMMAND"
>${array_name[0]}</B
>, the first
	element of the array.</P
><P
><A
NAME="EMPTYARRAY0"
></A
></P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="EMPTYARRAY"
></A
><P
><B
>Example 26-7. Of empty arrays and empty elements</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# empty-array.sh
   3&nbsp;
   4&nbsp;#  Thanks to Stephane Chazelas for the original example,
   5&nbsp;#+ and to Michael Zick and Omair Eshkenazi for extending it.
   6&nbsp;
   7&nbsp;
   8&nbsp;# An empty array is not the same as an array with empty elements.
   9&nbsp;
  10&nbsp;  array0=( first second third )
  11&nbsp;  array1=( '' )   # "array1" consists of one empty element.
  12&nbsp;  array2=( )      # No elements . . . "array2" is empty.
  13&nbsp;  array3=(   )    # What about this array?
  14&nbsp;
  15&nbsp;echo
  16&nbsp;ListArray()
  17&nbsp;{
  18&nbsp;echo
  19&nbsp;echo "Elements in array0:  ${array0[@]}"
  20&nbsp;echo "Elements in array1:  ${array1[@]}"
  21&nbsp;echo "Elements in array2:  ${array2[@]}"
  22&nbsp;echo "Elements in array3:  ${array3[@]}"
  23&nbsp;echo
  24&nbsp;echo "Length of first element in array0 = ${#array0}"
  25&nbsp;echo "Length of first element in array1 = ${#array1}"
  26&nbsp;echo "Length of first element in array2 = ${#array2}"
  27&nbsp;echo "Length of first element in array3 = ${#array3}"
  28&nbsp;echo
  29&nbsp;echo "Number of elements in array0 = ${#array0[*]}"  # 3
  30&nbsp;echo "Number of elements in array1 = ${#array1[*]}"  # 1  (Surprise!)
  31&nbsp;echo "Number of elements in array2 = ${#array2[*]}"  # 0
  32&nbsp;echo "Number of elements in array3 = ${#array3[*]}"  # 0
  33&nbsp;}
  34&nbsp;
  35&nbsp;# ===================================================================
  36&nbsp;
  37&nbsp;ListArray
  38&nbsp;
  39&nbsp;# Try extending those arrays.
  40&nbsp;
  41&nbsp;# Adding an element to an array.
  42&nbsp;array0=( "${array0[@]}" "new1" )
  43&nbsp;array1=( "${array1[@]}" "new1" )
  44&nbsp;array2=( "${array2[@]}" "new1" )
  45&nbsp;array3=( "${array3[@]}" "new1" )
  46&nbsp;
  47&nbsp;ListArray
  48&nbsp;
  49&nbsp;# or
  50&nbsp;array0[${#array0[*]}]="new2"
  51&nbsp;array1[${#array1[*]}]="new2"
  52&nbsp;array2[${#array2[*]}]="new2"
  53&nbsp;array3[${#array3[*]}]="new2"
  54&nbsp;
  55&nbsp;ListArray
  56&nbsp;
  57&nbsp;# When extended as above; arrays are 'stacks'
  58&nbsp;# The above is the 'push'
  59&nbsp;# The stack 'height' is:
  60&nbsp;height=${#array2[@]}
  61&nbsp;echo
  62&nbsp;echo "Stack height for array2 = $height"
  63&nbsp;
  64&nbsp;# The 'pop' is:
  65&nbsp;unset array2[${#array2[@]}-1]   #  Arrays are zero-based,
  66&nbsp;height=${#array2[@]}            #+ which means first element has index 0.
  67&nbsp;echo
  68&nbsp;echo "POP"
  69&nbsp;echo "New stack height for array2 = $height"
  70&nbsp;
  71&nbsp;ListArray
  72&nbsp;
  73&nbsp;# List only 2nd and 3rd elements of array0.
  74&nbsp;from=1		# Zero-based numbering.
  75&nbsp;to=2
  76&nbsp;array3=( ${array0[@]:1:2} )
  77&nbsp;echo
  78&nbsp;echo "Elements in array3:  ${array3[@]}"
  79&nbsp;
  80&nbsp;# Works like a string (array of characters).
  81&nbsp;# Try some other "string" forms.
  82&nbsp;
  83&nbsp;# Replacement:
  84&nbsp;array4=( ${array0[@]/second/2nd} )
  85&nbsp;echo
  86&nbsp;echo "Elements in array4:  ${array4[@]}"
  87&nbsp;
  88&nbsp;# Replace all matching wildcarded string.
  89&nbsp;array5=( ${array0[@]//new?/old} )
  90&nbsp;echo
  91&nbsp;echo "Elements in array5:  ${array5[@]}"
  92&nbsp;
  93&nbsp;# Just when you are getting the feel for this . . .
  94&nbsp;array6=( ${array0[@]#*new} )
  95&nbsp;echo # This one might surprise you.
  96&nbsp;echo "Elements in array6:  ${array6[@]}"
  97&nbsp;
  98&nbsp;array7=( ${array0[@]#new1} )
  99&nbsp;echo # After array6 this should not be a surprise.
 100&nbsp;echo "Elements in array7:  ${array7[@]}"
 101&nbsp;
 102&nbsp;# Which looks a lot like . . .
 103&nbsp;array8=( ${array0[@]/new1/} )
 104&nbsp;echo
 105&nbsp;echo "Elements in array8:  ${array8[@]}"
 106&nbsp;
 107&nbsp;#  So what can one say about this?
 108&nbsp;
 109&nbsp;#  The string operations are performed on
 110&nbsp;#+ each of the elements in var[@] in succession.
 111&nbsp;#  Therefore : Bash supports string vector operations
 112&nbsp;#+ if the result is a zero length string,
 113&nbsp;#+ that element disappears in the resulting assignment.
 114&nbsp;
 115&nbsp;#  Question, are those strings hard or soft quotes?
 116&nbsp;
 117&nbsp;zap='new*'
 118&nbsp;array9=( ${array0[@]/$zap/} )
 119&nbsp;echo
 120&nbsp;echo "Elements in array9:  ${array9[@]}"
 121&nbsp;
 122&nbsp;# Just when you thought you where still in Kansas . . .
 123&nbsp;array10=( ${array0[@]#$zap} )
 124&nbsp;echo
 125&nbsp;echo "Elements in array10:  ${array10[@]}"
 126&nbsp;
 127&nbsp;# Compare array7 with array10.
 128&nbsp;# Compare array8 with array9.
 129&nbsp;
 130&nbsp;# Answer: must be soft quotes.
 131&nbsp;
 132&nbsp;exit 0</PRE
></TD
></TR
></TABLE
><HR></DIV
><P
>The relationship of <B
CLASS="COMMAND"
>${array_name[@]}</B
>
	and <B
CLASS="COMMAND"
>${array_name[*]}</B
> is analogous to that
	between <A
HREF="variables2.html#APPREF"
>$@ and $*</A
>. This powerful
	array notation has a number of uses.</P
><P
><A
NAME="COPYARRAY0"
></A
></P
><P
>      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR