与sed，awk，tr和朋友删除尾随/开始的换行符 [英] Removing trailing / starting newlines with sed, awk, tr, and friends

问题描述

我想从文件中删除所有空行，但是仅当它们在文件的末尾/开始时才删除(也就是说，如果在它们之前没有非空行，则在开始处；以及如果在它们之后没有非空行，那么最后.)

I would like to remove all of the empty lines from a file, but only when they are at the end/start of a file (that is, if there are no non-empty lines before them, at the start; and if there are no non-empty lines after them, at the end.)

在诸如Perl或Ruby之类的功能齐全的脚本语言之外，这是否可能?如果可能，我希望使用sed或awk进行此操作.基本上，任何轻量级且广泛可用的UNIX-y工具都可以，特别是我可以快速了解更多的工具(因此，不包括Perl.)

Is this possible outside of a fully-featured scripting language like Perl or Ruby? I’d prefer to do this with sed or awk if possible. Basically, any light-weight and widely available UNIX-y tool would be fine, especially one I can learn more about quickly (Perl, thus, not included.)

推荐答案

来自 用于sed的单行脚本 :

From Useful one-line scripts for sed:

# Delete all leading blank lines at top of file (only).
sed '/./,$!d' file

# Delete all trailing blank lines at end of file (only).
sed -e :a -e '/^\n*$/{$d;N;};/\n$/ba' file

因此，要从文件中删除开头和结尾的空白行，可以将以上命令合并为:

Therefore, to remove both leading and trailing blank lines from a file, you can combine the above commands into:

sed -e :a -e '/./,$!d;/^\n*$/{$d;N;};/\n$/ba' file

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