# 暗无天日

=============>随便,谢谢

# 如何保留命令替换结果中的换行符

seq 1 2
echo "---------------------------------"
a=$(seq 1 2) echo$a

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2
---------------------------------
1 2


Command Substitution

.......

Bash  performs  the  expansion by executing command and replacing the
command substitution with the standard output of  the  command,  with
any  trailing  newlines  deleted.  *Embedded newlines are not deleted,
but they may be removed during word splitting.*  The command substitu‐
tion  $(cat file) can be replaced by the equivalent but faster$(<
file).

.......

*,If  the substitution appears within double quotes, word splitting and
pathname expansion are not performed on the results.*


Word Splitting
The shell scans the results of parameter expansion, command substitu‐
tion,  and  arithmetic  expansion  that  *did  not occur within double
quotes for word splitting*.

The shell treats each character of IFS as a delimiter, and splits the
results  of  the other expansions into words on these characters.  If
IFS is unset, or its  value  is  exactly  <space><tab><newline>,  the
default,  then  sequences  of  <space>,  <tab>,  and <newline> at the
beginning and end of the  results  of  the  previous  expansions  are
ignored,  and  any sequence of IFS characters not at the beginning or
end serves to delimit words.  If IFS  has  a  value  other  than  the
default,  then  sequences  of the whitespace characters space and tab
are ignored at the beginning and end of the  word,  as  long  as  the
whitespace  character is in the value of IFS (an IFS whitespace char‐
acter).  Any character in IFS that is not IFS whitespace, along  with
any adjacent IFS whitespace characters, delimits a field.  A sequence
of IFS whitespace characters is also treated as a delimiter.  If  the
value of IFS is null, no word splitting occurs.

Explicit  null  arguments ("" or '') are retained.  Unquoted implicit
null arguments, resulting from the expansion of parameters that  have
no  values,  are  removed.   If a parameter with no value is expanded
within double quotes, a null argument results and is retained.

Note that if no expansion occurs, no splitting is performed.


1. 把命令替换放到双引号中,如下所示:

a="$(seq 1 2)" echo "$a"

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2

2. IFS 设置为空，如下所示:

IFS=''
a=$(seq 1 2) echo$a

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