{"id":1574,"date":"2014-11-12T15:28:23","date_gmt":"2014-11-12T15:28:23","guid":{"rendered":"http:\/\/ixyzero.com\/blog\/?p=1574"},"modified":"2014-11-12T15:28:23","modified_gmt":"2014-11-12T15:28:23","slug":"%e5%a6%82%e4%bd%95%e8%8e%b7%e5%8f%96%e6%96%87%e4%bb%b6%e4%b8%ad%e7%9a%84%e6%9f%90%e4%b8%80%e8%a1%8c%ef%bc%9f","status":"publish","type":"post","link":"https:\/\/ixyzero.com\/blog\/archives\/1574.html","title":{"rendered":"\u5982\u4f55\u83b7\u53d6\u6587\u4ef6\u4e2d\u7684\u67d0\u4e00\u884c\uff1f"},"content":{"rendered":"

\u5728Stackoverflow\u4e0a\u770b\u5230\u4e00\u4e2a\u9898\u76ee”Shell\/Bash Command to get nth line of STDOUT<\/a>“\uff0c\u89c9\u5f97\u4e0d\u9519\uff0c\u5c1d\u8bd5\u4e86\u5176\u4e2d\u4ecb\u7ecd\u7684\u65b9\u6cd5\uff0c\u7136\u540e\u7ed3\u5408\u81ea\u5df1\u4e4b\u524d\u7684\u4e00\u4e9b\u5b66\u4e60\uff0c\u603b\u7ed3\/\u6458\u5f55\u81f3\u4e0b\u6587\uff1a<\/p>\n

\u7528Linux\u7684\u547d\u4ee4\u83b7\u53d6\u6587\u4ef6\u4e2d\u7684\u67d0\u4e00\u884c{Shell\/Bash Command to get nth line of STDOUT}<\/h6>\n

Is there any bash command that will let you get the nth line of STDOUT?
\nThat is to say, something that would take this<\/p>\n

$ ls -l\n-rw-r--r--@ 1 root wheel my.txt\n-rw-r--r--@ 1 root wheel files.txt\n-rw-r--r--@ 1 root wheel here.txt<\/pre>\n
and do something like<\/p>\n
$ ls -l | magic-command 2\n-rw-r--r--@ 1 root wheel files.txt<\/pre>\n
I realize this would be bad practice when writing scripts meant to be reused, BUT when working with the shell day to day it’d be useful to me to be able to filter my STDOUT in such a way.
\nI also realize this would be semi-trivial command to write (buffer STDOUT, return a specific line), but I want to know if there’s some standard<\/strong> shell command to do this that would be available without me dropping a script into place.<\/p>\n
\n
Using sed, just for variety:<\/p>\n
ls -l | sed -n 2p<\/pre>\n
Using this alternative, which looks more efficient since it stops reading the input when the required line is printed, may generate a SIGPIPE in the feeding process, which may in turn generate an unwanted error message:<\/p>\n
ls -l | sed -n -e '2{p;q}'<\/pre>\n
I’ve seen that often enough that I usually use the first (which is easier to type, anyway), though ls is not a command that complains when it gets SIGPIPE.
\nFor a range of lines:<\/p>\n
ls -l | sed -n 2,4p<\/pre>\n
For several ranges of lines:<\/p>\n
ls -l | sed -n -e 2,4p -e 20,30p\nls -l | sed -n -e '2,4p;20,30p'\nls -l | head -2 | tail -1<\/pre>\n
\n
Alternative to the nice head \/ tail way:<\/p>\n
ls -al | awk 'NR==2'<\/pre>\n
or<\/p>\n
ls -al | sed -n '2p'<\/pre>\n
\n
From sed1line<\/a>:<\/p>\n
# print line number 52\nsed -n '52p' # method 1\nsed '52!d' # method 2\nsed '52q;d' # method 3, efficient on large files<\/pre>\n
From awk1line<\/a>:<\/p>\n
# print line number 52\nawk 'NR==52'\nawk 'NR==52 {print;exit}' # more efficient on large files<\/pre>\n
\n
Try this sed version:<\/p>\n
ls -l | sed '2 ! d'<\/pre>\n
It says “delete all the lines that aren’t the second one”.<\/p>\n
\n
For the sake of completeness \ud83d\ude09
\nshorter code<\/p>\n
find \/ | awk NR==3<\/pre>\n
shorter life<\/p>\n
find \/ | awk 'NR==3 {print $0; exit}'<\/pre>\n
\n
Is Perl easily available to you?<\/p>\n
$ perl -n -e 'if ($. == 7) { print; exit(0); }'<\/pre>\n
\n
Obviously substitute whatever number you want for 7.
\nYou can use awk:<\/p>\n
ls -l | awk 'NR==2'<\/pre>\n
Update
\nThe above code will not get what we want because of off-by-one error: the ls -l command’s first line is the total line. For that, the following revised code will work:<\/p>\n
ls -l | awk 'NR==3'<\/pre>\n
\n
Another poster suggested<\/p>\n
ls -l | head -2 | tail -1<\/pre>\n
but if you pipe head into tail, it looks like everything up to line N is processed twice.
\nPiping tail into head<\/p>\n
ls -l | tail -n +2 | head -n1<\/pre>\n
would be more efficient?<\/p>\n
\u539f\u6587\u94fe\u63a5\uff1a<\/h6>\n
http:\/\/stackoverflow.com\/questions\/1429556\/shell-bash-command-to-get-nth-line-of-stdout<\/a><\/p>\n
\n
 <\/p>\n
\u5feb\u901f\u6253\u5370\u51fa\u6587\u4ef6\u4e2d\u95f4\u4f4d\u7f6e\u7684\u884c<\/h5>\n
1.sed\u548cawk<\/h6>\n
\u5047\u8bbe\u4f60\u9700\u898120\u81f340\u884c\u7684\u5185\u5bb9\uff1a<\/p>\n
sed -n '20,40p' file_name\n#\nawk 'FNR>=20 && FNR<=40' file_name<\/pre>\n
2.sed\u7684\u51e0\u79cd\u65b9\u5f0f\uff08\u6253\u5370\/\u663e\u793a\u6307\u5b9a\u884c\uff09<\/h6>\n
# print line number 52\nsed -n '52p' # method 1\nsed '52!d' # method 2\nsed '52q;d' # method 3, efficient on large files<\/pre>\n
method 3 efficient on large files<\/strong><\/span><\/p>\n
fastest way to display specific lines<\/p>\n
3.\u5148head\u7136\u540etail<\/h6>\n
\u5728Python\u4e2d\u53ef\u4ee5\u73b0\u5c06\u6587\u4ef6readlines()\u5230\u4e00\u4e2alist\u4e2d\uff0c\u7136\u540e\u4f7f\u7528list\u5207\u5272\u65b9\u6cd5\u8fdb\u884c\u67e5\u770b\u2014\u2014\u5bf9\u4e8e\u5c0f\u6587\u4ef6\u800c\u8a00\u3002<\/p>\n
4.\u5148\u5207\u5272\uff0c\u7136\u540e\u5206\u522b\u67e5\u770b<\/h6>\n
\u5148split\uff0c\u7136\u540egrep\u3001sed\u3001awk\u3001head\u3001tail<\/p>\n
\u53c2\u8003<\/strong>\uff1a<\/strong><\/span><\/h6>\n