37.3. Bash，版本 4
Chet Ramey 于 2009 年 2 月 20 日发布了 Bash 版本 4。此版本具有许多重要的新功能，以及一些重要的错误修复。
新功能包括
关联数组。[1]
示例 37-5. 一个简单的地址数据库
#!/bin/bash4 # fetch_address.sh declare -A address # -A option declares associative array. address[Charles]="414 W. 10th Ave., Baltimore, MD 21236" address[John]="202 E. 3rd St., New York, NY 10009" address[Wilma]="1854 Vermont Ave, Los Angeles, CA 90023" echo "Charles's address is ${address[Charles]}." # Charles's address is 414 W. 10th Ave., Baltimore, MD 21236. echo "Wilma's address is ${address[Wilma]}." # Wilma's address is 1854 Vermont Ave, Los Angeles, CA 90023. echo "John's address is ${address[John]}." # John's address is 202 E. 3rd St., New York, NY 10009. echo echo "${!address[*]}" # The array indices ... # Charles John Wilma示例 37-6. 一个稍微复杂的地址数据库
#!/bin/bash4 # fetch_address-2.sh # A more elaborate version of fetch_address.sh. SUCCESS=0 E_DB=99 # Error code for missing entry. declare -A address # -A option declares associative array. store_address () { address[$1]="$2" return $? } fetch_address () { if [[ -z "${address[$1]}" ]] then echo "$1's address is not in database." return $E_DB fi echo "$1's address is ${address[$1]}." return $? } store_address "Lucas Fayne" "414 W. 13th Ave., Baltimore, MD 21236" store_address "Arvid Boyce" "202 E. 3rd St., New York, NY 10009" store_address "Velma Winston" "1854 Vermont Ave, Los Angeles, CA 90023" # Exercise: # Rewrite the above store_address calls to read data from a file, #+ then assign field 1 to name, field 2 to address in the array. # Each line in the file would have a format corresponding to the above. # Use a while-read loop to read from file, sed or awk to parse the fields. fetch_address "Lucas Fayne" # Lucas Fayne's address is 414 W. 13th Ave., Baltimore, MD 21236. fetch_address "Velma Winston" # Velma Winston's address is 1854 Vermont Ave, Los Angeles, CA 90023. fetch_address "Arvid Boyce" # Arvid Boyce's address is 202 E. 3rd St., New York, NY 10009. fetch_address "Bozo Bozeman" # Bozo Bozeman's address is not in database. exit $? # In this case, exit code = 99, since that is function return.有关关联数组的有趣用法，请参阅示例 A-53。
索引数组的元素可以包含嵌入的空格字符，甚至前导和/或尾随空格字符。但是，包含仅空白的索引数组元素是不允许的。
address[ ]="Blank" # Error!
case 结构增强：;;&和;&终止符。
示例 37-7. 测试字符
#!/bin/bash4 test_char () { case "$1" in [[:print:]] ) echo "$1 is a printable character.";;& # | # The ;;& terminator continues to the next pattern test. | [[:alnum:]] ) echo "$1 is an alpha/numeric character.";;& # v [[:alpha:]] ) echo "$1 is an alphabetic character.";;& # v [[:lower:]] ) echo "$1 is a lowercase alphabetic character.";;& [[:digit:]] ) echo "$1 is an numeric character.";& # | # The ;& terminator executes the next statement ... # | %%%@@@@@ ) echo "********************************";; # v # ^^^^^^^^ ... even with a dummy pattern. esac } echo test_char 3 # 3 is a printable character. # 3 is an alpha/numeric character. # 3 is an numeric character. # ******************************** echo test_char m # m is a printable character. # m is an alpha/numeric character. # m is an alphabetic character. # m is a lowercase alphabetic character. echo test_char / # / is a printable character. echo # The ;;& terminator can save complex if/then conditions. # The ;& is somewhat less useful.新的 coproc 内置命令使两个并行进程能够通信和交互。正如 Chet Ramey 在Bash FAQ [2] ver. 4.01 中所述
有一个新的 'coproc' 保留字，用于指定协进程
一个异步命令，运行并带有两个管道连接到创建它的
shell。协进程可以被命名。输入和输出文件描述符
以及协进程的 PID 在调用 shell 中可用
变量，这些变量带有特定于协进程的名称。
George Dimitriu 解释说，
"... coproc ... 是 Bash 进程替换中使用的功能，
现在已公开可用。"
这意味着它可以在脚本中显式调用，而不是
仅仅是 Bash 在幕后使用的机制。
协进程使用文件描述符。文件描述符使进程和管道能够通信。
#!/bin/bash4 # A coprocess communicates with a while-read loop. coproc { cat mx_data.txt; sleep 2; } # ^^^^^^^ # Try running this without "sleep 2" and see what happens. while read -u ${COPROC[0]} line # ${COPROC[0]} is the do #+ file descriptor of the coprocess. echo "$line" | sed -e 's/line/NOT-ORIGINAL-TEXT/' done kill $COPROC_PID # No longer need the coprocess, #+ so kill its PID.但是，请小心！
#!/bin/bash4 echo; echo a=aaa b=bbb c=ccc coproc echo "one two three" while read -u ${COPROC[0]} a b c; # Note that this loop do #+ runs in a subshell. echo "Inside while-read loop: "; echo "a = $a"; echo "b = $b"; echo "c = $c" echo "coproc file descriptor: ${COPROC[0]}" done # a = one # b = two # c = three # So far, so good, but ... echo "-----------------" echo "Outside while-read loop: " echo "a = $a" # a = echo "b = $b" # b = echo "c = $c" # c = echo "coproc file descriptor: ${COPROC[0]}" echo # The coproc is still running, but ... #+ it still doesn't enable the parent process #+ to "inherit" variables from the child process, the while-read loop. # Compare this to the "badread.sh" script.协进程是异步的，这可能会导致问题。它可能在另一个进程完成与其通信之前终止。
#!/bin/bash4 coproc cpname { for i in {0..10}; do echo "index = $i"; done; } # ^^^^^^ This is a *named* coprocess. read -u ${cpname[0]} echo $REPLY # index = 0 echo ${COPROC[0]} #+ No output ... the coprocess timed out # after the first loop iteration. # However, George Dimitriu has a partial fix. coproc cpname { for i in {0..10}; do echo "index = $i"; done; sleep 1; echo hi > myo; cat - >> myo; } # ^^^^^ This is a *named* coprocess. echo "I am main"$'\04' >&${cpname[1]} myfd=${cpname[0]} echo myfd=$myfd ### while read -u $myfd ### do ### echo $REPLY; ### done echo $cpname_PID # Run this with and without the commented-out while-loop, and it is #+ apparent that each process, the executing shell and the coprocess, #+ waits for the other to finish writing in its own write-enabled pipe.新的 mapfile 内置命令使得加载包含文本文件内容的数组成为可能，而无需使用循环或命令替换。
#!/bin/bash4 mapfile Arr1 < $0 # Same result as Arr1=( $(cat $0) ) echo "${Arr1[@]}" # Copies this entire script out to stdout. echo "--"; echo # But, not the same as read -a !!! read -a Arr2 < $0 echo "${Arr2[@]}" # Reads only first line of script into the array. exitread 内置命令进行了一些小的改进。-t timeout 选项现在接受（十进制）小数值 [3]，并且-i选项允许预加载编辑缓冲区。[4] 不幸的是，这些增强功能仍在开发中，尚未（还）在脚本中可用。
参数替换获得了大小写修改运算符。
#!/bin/bash4 var=veryMixedUpVariable echo ${var} # veryMixedUpVariable echo ${var^} # VeryMixedUpVariable # * First char --> uppercase. echo ${var^^} # VERYMIXEDUPVARIABLE # ** All chars --> uppercase. echo ${var,} # veryMixedUpVariable # * First char --> lowercase. echo ${var,,} # verymixedupvariable # ** All chars --> lowercase.declare 内置命令现在接受-l 小写和-c 首字母大写选项。
#!/bin/bash4 declare -l var1 # Will change to lowercase var1=MixedCaseVARIABLE echo "$var1" # mixedcasevariable # Same effect as echo $var1 | tr A-Z a-z declare -c var2 # Changes only initial char to uppercase. var2=originally_lowercase echo "$var2" # Originally_lowercase # NOT the same effect as echo $var2 | tr a-z A-Z
花括号展开有更多选项。
递增/递减，在花括号内的最后一项中指定。
#!/bin/bash4 echo {40..60..2} # 40 42 44 46 48 50 52 54 56 58 60 # All the even numbers, between 40 and 60. echo {60..40..2} # 60 58 56 54 52 50 48 46 44 42 40 # All the even numbers, between 40 and 60, counting backwards. # In effect, a decrement. echo {60..40..-2} # The same output. The minus sign is not necessary. # But, what about letters and symbols? echo {X..d} # X Y Z [ ] ^ _ ` a b c d # Does not echo the \ which escapes a space.零填充，在花括号内的第一项中指定，在输出中的每一项前缀相同数量的零。
bash4$ echo {010..15} 010 011 012 013 014 015 bash4$ echo {000..10} 000 001 002 003 004 005 006 007 008 009 010位置参数的子字符串提取现在以 $0 作为零索引开始。（这纠正了位置参数处理中的不一致性。）
#!/bin/bash # show-params.bash # Requires version 4+ of Bash. # Invoke this scripts with at least one positional parameter. E_BADPARAMS=99 if [ -z "$1" ] then echo "Usage $0 param1 ..." exit $E_BADPARAMS fi echo ${@:0} # bash3 show-params.bash4 one two three # one two three # bash4 show-params.bash4 one two three # show-params.bash4 one two three # $0 $1 $2 $3新的 ** globbing 运算符递归地匹配文件名和目录。
#!/bin/bash4 # filelist.bash4 shopt -s globstar # Must enable globstar, otherwise ** doesn't work. # The globstar shell option is new to version 4 of Bash. echo "Using *"; echo for filename in * do echo "$filename" done # Lists only files in current directory ($PWD). echo; echo "--------------"; echo echo "Using **" for filename in ** do echo "$filename" done # Lists complete file tree, recursively. exit Using * allmyfiles filelist.bash4 -------------- Using ** allmyfiles allmyfiles/file.index.txt allmyfiles/my_music allmyfiles/my_music/me-singing-60s-folksongs.ogg allmyfiles/my_music/me-singing-opera.ogg allmyfiles/my_music/piano-lesson.1.ogg allmyfiles/my_pictures allmyfiles/my_pictures/at-beach-with-Jade.png allmyfiles/my_pictures/picnic-with-Melissa.png filelist.bash4新的 $BASHPID 内部变量。
有一个新的 builtin 错误处理函数，名为 command_not_found_handle。
#!/bin/bash4 command_not_found_handle () { # Accepts implicit parameters. echo "The following command is not valid: \""$1\""" echo "With the following argument(s): \""$2\"" \""$3\""" # $4, $5 ... } # $1, $2, etc. are not explicitly passed to the function. bad_command arg1 arg2 # The following command is not valid: "bad_command" # With the following argument(s): "arg1" "arg2"
编者评论 关联数组？协进程？我们已经了解和喜爱的精简 Bash 发生了什么？它是否正在遭受（可怕的！）“功能蔓延”？或者甚至可能是 Korn shell 羡慕？ 给 Chet Ramey 的注释：请在未来的 Bash 版本中仅添加必要的功能——也许是 for-each 循环和对多维数组的支持。[5] 大多数 Bash 用户不需要、不会使用，并且可能不会非常欣赏复杂的“功能”，例如内置调试器、Perl 接口和外挂式火箭助推器。 |
37.3.1. Bash，版本 4.1
Bash 版本 4.1 于 2010 年 5 月发布，主要是错误修复更新。
在双括号内，> 和 < 字符串比较运算符现在符合locale。由于 locale 设置可能会影响字符串表达式的排序顺序，因此这对 [[ ... ]] 表达式内的比较测试具有副作用。
read 内置命令现在接受-N选项（read -N chars），这会导致 read 在读取 chars 个字符后终止。
嵌入在 $( ... ) 命令替换构造中的 Here 文档 可以用简单的 ) 终止。
示例 37-9. 使用here 文档设置变量
#!/bin/bash # here-commsub.sh # Requires Bash version -ge 4.1 ... multi_line_var=$( cat <<ENDxxx ------------------------------ This is line 1 of the variable This is line 2 of the variable This is line 3 of the variable ------------------------------ ENDxxx) # Rather than what Bash 4.0 requires: #+ that the terminating limit string and #+ the terminating close-parenthesis be on separate lines. # ENDxxx # ) echo "$multi_line_var" # Bash still emits a warning, though. # warning: here-document at line 10 delimited #+ by end-of-file (wanted `ENDxxx')
37.3.2. Bash，版本 4.2
Bash 版本 4.2 于 2011 年 2 月发布，除了错误修复外，还包含许多新功能和增强功能。
Bash 现在支持\u和\U Unicode 转义。
echo -e '\u2630' # Horizontal triple bar character. # Equivalent to the more roundabout: echo -e "\xE2\x98\xB0" # Recognized by earlier Bash versions. echo -e '\u220F' # PI (Greek letter and mathematical symbol) echo -e '\u0416' # Capital "ZHE" (Cyrillic letter) echo -e '\u2708' # Airplane (Dingbat font) symbol echo -e '\u2622' # Radioactivity trefoil echo -e "The amplifier circuit requires a 100 \u2126 pull-up resistor." unicode_var='\u2640' echo -e $unicode_var # Female symbol printf "$unicode_var \n" # Female symbol, with newline # And for something a bit more elaborate . . . # We can store Unicode symbols in an associative array, #+ then retrieve them by name. # Run this in a gnome-terminal or a terminal with a large, bold font #+ for better legibility. declare -A symbol # Associative array. symbol[script_E]='\u2130' symbol[script_F]='\u2131' symbol[script_J]='\u2110' symbol[script_M]='\u2133' symbol[Rx]='\u211E' symbol[TEL]='\u2121' symbol[FAX]='\u213B' symbol[care_of]='\u2105' symbol[account]='\u2100' symbol[trademark]='\u2122' echo -ne "${symbol[script_E]} " echo -ne "${symbol[script_F]} " echo -ne "${symbol[script_J]} " echo -ne "${symbol[script_M]} " echo -ne "${symbol[Rx]} " echo -ne "${symbol[TEL]} " echo -ne "${symbol[FAX]} " echo -ne "${symbol[care_of]} " echo -ne "${symbol[account]} " echo -ne "${symbol[trademark]} " echo
上面的示例使用了 $' ... ' 字符串展开构造。
当lastpipeshell 选项被设置时，管道中的最后一个命令不在子 shell 中运行。
示例 37-10. 将输入通过管道传递给 read
#!/bin/bash # lastpipe-option.sh line='' # Null value. echo "\$line = "$line"" # $line = echo shopt -s lastpipe # Error on Bash version -lt 4.2. echo "Exit status of attempting to set \"lastpipe\" option is $?" # 1 if Bash version -lt 4.2, 0 otherwise. echo head -1 $0 | read line # Pipe the first line of the script to read. # ^^^^^^^^^ Not in a subshell!!! echo "\$line = "$line"" # Older Bash releases $line = # Bash version 4.2 $line = #!/bin/bash
负数组索引允许从数组末尾向后计数。
示例 37-11. 负数组索引
#!/bin/bash # neg-array.sh # Requires Bash, version -ge 4.2. array=( zero one two three four five ) # Six-element array. # 0 1 2 3 4 5 # -6 -5 -4 -3 -2 -1 # Negative array indices now permitted. echo ${array[-1]} # five echo ${array[-2]} # four # ... echo ${array[-6]} # zero # Negative array indices count backward from the last element+1. # But, you cannot index past the beginning of the array. echo ${array[-7]} # array: bad array subscript # So, what is this new feature good for? echo "The last element in the array is "${array[-1]}"" # Which is quite a bit more straightforward than: echo "The last element in the array is "${array[${#array[*]}-1]}"" echo # And ... index=0 let "neg_element_count = 0 - ${#array[*]}" # Number of elements, converted to a negative number. while [ $index -gt $neg_element_count ]; do ((index--)); echo -n "${array[index]} " done # Lists the elements in the array, backwards. # We have just simulated the "tac" command on this array. echo # See also neg-offset.sh.子字符串提取使用负长度参数来指定距目标字符串末尾的偏移量。
示例 37-12. 字符串提取构造中的负参数
#!/bin/bash # Bash, version -ge 4.2 # Negative length-index in substring extraction. # Important: It changes the interpretation of this construct! stringZ=abcABC123ABCabc echo ${stringZ} # abcABC123ABCabc # Position within string: 0123456789..... echo ${stringZ:2:3} # cAB # Count 2 chars forward from string beginning, and extract 3 chars. # ${string:position:length} # So far, nothing new, but now ... # abcABC123ABCabc # Position within string: 0123....6543210 echo ${stringZ:3:-6} # ABC123 # ^ # Index 3 chars forward from beginning and 6 chars backward from end, #+ and extract everything in between. # ${string:offset-from-front:offset-from-end} # When the "length" parameter is negative, #+ it serves as an offset-from-end parameter. # See also neg-array.sh.