数组上的 Bash 子串扩展
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Bash substring expansion on array
提问by H?kon H?gland
I have a set of files with a given suffix. For instance, I have a set of pdf files with suffix .pdf. I would like to obtain the names of the files without the suffix using substring expansion.
我有一组带有给定后缀的文件。例如，我有一组后缀为 .pdf 的 pdf 文件.pdf。我想使用子字符串扩展获取没有后缀的文件名。
For a single file I can use:
对于单个文件，我可以使用：
file="test.pdf"
echo ${file:0 -4}
To do this operation for all files, I now tried:
要对所有文件执行此操作，我现在尝试：
files=( $(ls *.pdf) )
ff=( "${files[@]:0: -4}" )
echo ${ff[@]}
I now get an error saying that substring expression < 0..
我现在收到一个错误说substring expression < 0..
( I would like to avoid using a forloop )
（我想避免使用for循环）
回答by gniourf_gniourf
Use parameter expansionsto remove the .pdfpart like so:
使用参数扩展来删除.pdf部分，如下所示：
shopt -s nullglob
files=( *.pdf )
echo "${files[@]%.pdf}"
The shopt -s nullglobis always a good idea when using globs: it will make the glob expand to nothing if there are no matches.
在shopt -s nullglob使用时，水珠总是一个好主意：它将使水珠扩大到什么，如果没有匹配。
"${files[@]%.pdf}"will expand to an array with all the trailing .pdfremoved. You can, if you wish put this in another array as so:
"${files[@]%.pdf}"将扩展为.pdf删除所有尾随的数组。你可以，如果你想把它放在另一个数组中：
files_noext=( "${files[@]%.pdf}" )
All this is 100% safe regarding funny symbols in filenames (spaces, newlines, etc.), except for the echopart for files named -n.pdf, -e.pdfand -E.pdf... but the echowas just here for demonstration purposes. Your files=( $(ls *.pdf) )is really really bad! Do never parse the output of ls.
对于文件名中的有趣符号（空格、换行符等），所有这些都是 100% 安全的，除了echo名为-n.pdf,-e.pdf和-E.pdf... 的文件部分，但echo这里只是为了演示目的。你files=( $(ls *.pdf) )真的很糟糕！永远不要解析ls.
To answer your comment: substring expansions don't work on each field of the array. Taken from the reference manual linked above:
回答您的评论：子字符串扩展不适用于数组的每个字段。取自上面链接的参考手册：
${parameter:offset}
${parameter:offset:length}If
offsetevaluates to a number less than zero, the value is used as an offset from the end of the value ofparameter. Iflengthevaluates to a number less than zero, andparameteris not@and not an indexed or associative array, it is interpreted as an offset from the end of the value ofparameterrather than a number of characters, and the expansion is the characters between the two offsets. Ifparameteris@, the result islengthpositional parameters beginning at offset. Ifparameteris an indexed array name subscripted by@or*, the result is thelengthmembers of the array beginning with${parameter[offset]}.A negative offset is taken relative to one greater than the maximum index of the specified array. Substring expansion applied to an associative array produces undefined results.
${parameter:offset}
${parameter:offset:length}如果
offset计算结果为小于零的数字，则该值用作距 的值末尾的偏移量parameter。如果length计算结果为小于零的数字，并且parameter不是@索引或关联数组，则将其解释为距值末尾的偏移量parameter而不是多个字符，并且扩展是两个偏移量之间的字符. 如果parameter是@，则结果是length从偏移量开始的位置参数。如果parameter是一个以@或为下标的索引数组名称*，则结果为以length开头的数组成员${parameter[offset]}。相对于大于指定数组的最大索引的一个负偏移量。应用于关联数组的子字符串扩展会产生未定义的结果。
So, e.g.,
所以，例如，
$ array=( zero one two three four five six seven eight )
$ echo "${array[@]:3:2}"
three four
$
