bash 如何使用 sed 从字符串中删除前 X 个字符？
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How can I strip first X characters from string using sed?
提问by Kokesh
I am writing shell script for embedded Linux in a small industrial box. I have a variable containing the text pid: 1234and I want to strip first X characters from the line, so only 1234 stays. I have more variables I need to "clean", so I need to cut away X first characters and ${string:5}doesn't work for some reason in my system.
我正在一个小型工业盒子中为嵌入式 Linux 编写 shell 脚本。我有一个包含文本的变量pid: 1234，我想从行中删除前 X 个字符，所以只有 1234 保留。我有更多的变量需要“清理”，所以我需要删除 X 个第一个字符，${string:5}并且由于某种原因在我的系统中不起作用。
The only thing the box seems to have is sed.
盒子里似乎只有sed.
I am trying to make the following to work:
我正在尝试使以下内容起作用：
result=$(echo "$pid" | sed 's/^.\{4\}//g')
Any ideas?
有任何想法吗？
采纳答案by Arnaud F.
This will do the job too:
这也将完成这项工作：
echo "$pid"|awk '{print }'
回答by chepner
The following should work:
以下应该工作：
var="pid: 1234"
var=${var:5}
Are you sure bashis the shell executing your script?
你确定bashshell 正在执行你的脚本吗？
Even the POSIX-compliant
即使是符合 POSIX 的
var=${var#?????}
would be preferable to using an external process, although this requires you to hard-code the 5 in the form of a fixed-length pattern.
比使用外部过程更可取，尽管这需要您以固定长度模式的形式对 5 进行硬编码。
回答by Randy the Dev
Here's a concise method to cut the first X characters using cut(1). This example removes the first 4 characters by cutting a substring starting with 5th character.
这是使用cut(1). 此示例通过剪切从第 5 个字符开始的子字符串来删除前 4 个字符。
echo "$pid" | cut -c 5-
回答by Mark Longair
Use the -roption ("use extended regular expressions in the script") to sedin order to use the {n}syntax:
使用-r选项（“在脚本中使用扩展正则表达式”）sed以使用以下{n}语法：
$ echo 'pid: 1234'| sed -r 's/^.{5}//'
1234
回答by dtp70
Cut first two characters from string:
从字符串中剪切前两个字符：
$ string="1234567890"; echo "${string:2}"
34567890
回答by Ben
pipe it through awk '{print substr($0,42)}'where 42 is one more than the number of characters to drop. For example:
将它通过管道，awk '{print substr($0,42)}'其中 42 比要删除的字符数多 1。例如：
$ echo abcde| awk '{print substr([me@home]$ echo "pid: 1234" | cut -d" " -f2
1234
,2)}'
bcde
$
回答by Shawn Chin
回答by Mecki
Well, there have been solutions here with sed, awk, cutand using bashsyntax. I just want to throw in another POSIX conform variant:
那么，有这里已经解决方案sed，awk，cut以及使用bash的语法。我只想加入另一个符合 POSIX 的变体：
result=`echo $pid | cut -c 5-`
-ctells tail at which byte offset to start, counting from the end of the input data, yet if the the number starts with a +sign, it is from the beginning of the input data to the end.
-c告诉tail从哪个字节偏移开始，从输入数据的末尾开始计数，但如果数字以+符号开头，则是从输入数据的开头到结尾。
回答by Evgeny
Another way, using cutinstead of sed.
另一种方式，使用cut代替sed.
result=\`echo "$pid" | sed '/./ { s/pid:\ //g; }'\``
回答by treehead
I found the answer in pure sed supplied by this question(admittedly, posted after this question was posted). This does exactly what you asked, solely in sed:
我在这个问题提供的纯 sed 中找到了答案（诚然，在发布这个问题之后发布）。这完全符合您的要求，仅在 sed 中：
# Uncomment a line:
sed -i '/#\ COMMENTED_LINE_TO_MATCH/ { s/#\ //g; }' /path/to/target/file
The dot in sed '/./) is whatever you want to match. Your question is exactly what I was attempting to, except in my case I wanted to match a specific line in a file and then uncomment it. In my case it was:
) 中的点sed '/./是您想要匹配的任何内容。你的问题正是我想要的，除了在我的情况下，我想匹配文件中的特定行然后取消注释。就我而言，它是：
The -iafter sedis to edit the file in place (remove this switch if you want to test your matching expression prior to editing the file).
在-i之后sed是编辑而不是文件（如果你想编辑文件之前，测试你的匹配表达式删除此开关）。
(FTR, I posted this answer not for credit, but simply because I wanted to do this entirely with sed as this question asked and none of the previous answered solved that problem.)
（FTR，我发布这个答案不是为了信用，而仅仅是因为我想在提出这个问题时完全使用 sed 来做到这一点，而且之前的回答都没有解决这个问题。）
