bash 如果在使用 read 时没有以换行符 (\n) 终止，则尊重最后一行
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Respect last line if it's not terminated with a new line char (\n) when using read
提问by michaelmeyer
I have noticed for a while that readnever actually reads the last line of a file if there is not, at the end of it, a "newline" character. This is understandable if one consider that, as long as there is not a "newline" character in a file, it is as if it contained 0 line (which is quite difficult to admit !). See, for example, the following:
一段时间以来，我注意到read如果文件末尾没有“换行符”字符，则它永远不会真正读取文件的最后一行。这是可以理解的，如果有人认为，只要文件中没有“换行”字符，就好像它包含 0 行（这很难承认！）。例如，请参阅以下内容：
$ echo 'foo' > bar ; wc -l bar
1 bar
But...
但...
$ echo -n 'bar' > foo ; wc -l foo
0 foo
The question is then: how can I handle such situations when using readto process files which have not been created or modified by myself, and about which I don't know if they actually end up with a "newline" character ?
那么问题是：在read用于处理不是由我自己创建或修改的文件时，我如何处理这种情况，我不知道它们是否真的以“换行符”结束？
回答by kopischke
readdoes, in fact, read an unterminated line into the assigned var ($REPLYby default). It also returns false on such a line, which just means ‘end of file'; directly using its return value in the classic whileloop thus skips that one last line. If you change the loop logic slightly, you can process non-new line terminated files correctly, without need for prior sanitisation, with read:
read实际上，确实将未终止的行读入分配的 var（$REPLY默认情况下）。它还在这样的行上返回 false，这仅表示“文件结束”；直接在经典while循环中使用它的返回值从而跳过最后一行。如果您稍微更改循环逻辑，您可以正确处理非新行终止的文件，无需事先清理，使用read：
while read -r || [[ -n "$REPLY" ]]; do
# your processing of $REPLY here
done < "/path/to/file"
Note this is much faster than solutions relying on externals.
请注意，这比依赖外部的解决方案快得多。
Hat tip to Gordon Davissonfor improving the loop logic.
帽尖到戈登戴维森用于改善循环逻辑。
回答by JakeGould
POSIX requires any line in a file have a newline character at the end to denote it is a line. But this siteoffers a solution to exactly the scenario you are describing. Final product is this chunklet.
POSIX 要求文件中的任何行在末尾都有一个换行符来表示它是一行。但是该站点为您所描述的场景提供了一个解决方案。最终产品是这个小块。
newline='
'
lastline=$(tail -n 1 file; echo x); lastline=${lastline%x}
[ "${lastline#"${lastline%?}"}" != "$newline" ] && echo >> file
# Now file is sane; do our normal processing here...
回答by EJK
If you must use read, try this:
如果你必须使用 read，试试这个：
awk '{ print (cat file; tail -c1 file | grep -qx . && echo) | while read line
do
...
done
}' foo | while read line; do
echo the line is $line
done
as awk seems to recognize lines even without the newline char
因为即使没有换行符，awk 似乎也能识别行
回答by user123444555621
This is more or less a combination of the answers given so far.
这或多或少是迄今为止给出的答案的组合。
It does not modify the files in place.
它不会就地修改文件。
##代码##