如何从 bash 变量回显/打印特定行
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how can I echo/print specific lines from a bash variable
提问by lacrosse1991
I am trying to print specific lines from a multi-line bash variable. I've found the following:
我正在尝试从多行 bash 变量打印特定行。我发现了以下内容：
while read line; do echo LINE: "$line"; done <<< "$x"
where x would be the variable, but that simply prints out all lines instead of just a single one (say line 1 for instance). How could I go about adapting this to print out a specific line instead of all of them? (would like to avoid having to write the variable to a file instead)
其中 x 将是变量，但这只是打印出所有行而不是单行（例如第 1 行）。我该如何调整它以打印出特定的行而不是所有的行？（希望避免将变量写入文件）
回答by William Pursell
To print the Nth line:
打印第 N 行：
sed -n ${N}p <<< "$x"
or (more portably):
或（更便携）：
sed -n ${N}p << EOF
$x
EOF
or
或者
echo "$x" | sed -n "$N"p
or
或者
echo "$x" | sed -n ${N}p
or (for the specific case N==3)
或（对于特定情况 N==3）
echo "$x" | sed -n 3p
or
或者
while read line; do echo LINE: "$line"; done <<< "$x" | sed -n ${N}p
or
或者
while read line; do echo LINE: "$line"; done << EOF | sed -n ${N}p
$x
EOF
回答by FatalError
You can split it into an array like:
您可以将其拆分为一个数组，例如：
IFS=$'\n' lines=($x)
Then you can access any line by indexing the array, e.g.:
然后您可以通过索引数组来访问任何行，例如：
echo ${lines[1]}
(of course, lines[0]is "line 1").
（当然lines[0]是“第1行”）。
回答by ghoti
If you don't want to use an array for some reason, and you want to do this within bash rather than by spawning an external tool like sed, you can simply count lines:
如果您出于某种原因不想使用数组，并且您想在 bash 中执行此操作而不是通过生成外部工具（如 ）sed，则可以简单地计算行数：
[ghoti@pc ~]$ x=$'one\ntwo\nthree\nfour\nfive\n'
[ghoti@pc ~]$ n=3
[ghoti@pc ~]$ for (( c=0; c<n; c++ )); do read line; done <<< "$x"
[ghoti@pc ~]$ echo $line
three
[ghoti@pc ~]$
Or using one fewer variable:
或者少使用一个变量：
[ghoti@pc ~]$ n=2
[ghoti@pc ~]$ for (( ; n>0; n-- )); do read line; done <<< "$x"
[ghoti@pc ~]$ echo $line
two
These methods use what's sometimes called a "three expression for loop". It's a construct that's common in many languages, from bash to awk to perl to PHP to C (but not Python!). Getting to know them will help your programming in general.
这些方法使用有时称为“循环的三个表达式”的方法。这是一种在许多语言中都很常见的结构，从 bash 到 awk 到 perl，再到 PHP 到 C（但不是 Python！）。了解它们将有助于您的编程。
Though ... you probably don't want to be using bash to learn "real" programming. :-)
虽然……您可能不想使用 bash 来学习“真正的”编程。:-)
