[英]Replace entire line with bash variable using sed
I want to use sed to replace the entire line at a match with a bash variable. 我想用sed在比赛中用bash变量替换整行。 Replacing with plain text is fine.
用纯文本替换就可以了。
$ echo -e "foo bar\nfooy bary\nfoot bart" | sed '/fooy/c\text'
foo bar
text
foot bart
If the text I want to replace with is stored in a bash variable, however, this does not work. 但是,如果我要替换的文本存储在bash变量中,则此方法不起作用。
$ var="This is poetry."
$ echo -e "foo bar\nfooy bary\nfoot bart" | sed "/fooy/c\$var"
foo bar
$var
foot bart
How can I achieve this? 我该如何实现?
If you want to do this with sed (which you shouldn't, see below), use 如果您想使用sed进行此操作(不应该这样做,请参见下文),请使用
sed "/fooy/c\\$var"
This is a shell expansion problem. 这是外壳扩展问题。
\\$
in a doubly quoted string means a literal dollar, so $var
is not expanded. 用双引号引起来的
\\$
表示文字美元,因此$var
不会扩展。 GNU sed also accepts GNU sed也接受
sed "/fooy/c$var"
as long as you don't specify --posix
, but BSD sed (as you may have on FreeBSD or MacOS X) will complain about it. 只要您不指定
--posix
,但BSD sed(可能在FreeBSD或MacOS X上就可以)都会对此抱怨。
However, doing this with sed is not a good idea. 但是,使用sed执行此操作不是一个好主意。 Substituting shell variables into sed code is almost never a good idea, because it makes you vulnerable to code injection.
将shell变量替换为sed代码几乎不是一个好主意,因为它使您容易受到代码注入的攻击。 Take, for example,
举个例子
$ var=$(echo -e 'something\nd')
$ echo -e "foo bar\nfooy bary\nfoot bart" | sed --posix "/fooy/c\\$var"
something
That wasn't what we expected, was it? 那不是我们所期望的,是吗? What happens here is that
sed
, since it is unable do distinguish what you want it to treat as data ( $var
) and code, treats $var
as code, and therefore it treats the d
after the \\n
in it as a command (to delete the current line). 此处发生的是
sed
,因为它无法区分想要将其视为数据( $var
)和代码,将$var
视为代码,因此它将\\n
后的d
视为命令(删除当前行)。 A better way is to use awk
: 更好的方法是使用
awk
:
$ var=$(echo -e 'something\nd')
$ echo -e "foo bar\nfooy bary\nfoot bart" | awk -v var="$var" '/fooy/ { print var; next } 1'
foo bar
something
d
foot bart
This sidesteps the code injection issue by not treating $var
as code. 通过不将
$var
视为代码来避开代码注入问题。
Don't escape the $
symbol. 不要逃避
$
符号。 In bash, variables are referred by $variable-name
. 在bash中,变量由
$variable-name
引用。 If you do escaping the $
symbol, then the bash won't consider it as a variable. 如果您确实转义了
$
符号,则bash不会将其视为变量。 It would treat $var
as literal $var
. 它将
$var
当作文字$var
。
$ echo -e "foo bar\nfooy bary\nfoot bart" | sed "/fooy/c$var"
foo bar
This is poetry.
foot bart
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