我需要在 grep 输出之前查看 5 行。
我使用了命令，
grep -B 5 pattern filename
但是抛出了错误
/usr/bin/grep: illegal option --B如何处理这种情况并查看grep语句之前的5行？
您考虑过使用
awk如果这是一个可行的选项，请选中这一行：
$ awk '/PATTERN/{for(i=1;i<=x;)print a[i++];print}{for(i=1;i<x;i++)a[i]=a[i+1];a[x]=$0;}' x=5 file
上面的命令将返回匹配模式之前的五行和匹配的模式（即总共 6 行，而
grep -B 5x我希望这有帮助。
Simply_Me 的答案是正确的，但会复制每个不匹配项上的所有先前行。 （挑剔的技术细节：即使 gawk 的实现避免了复制字符串本身，它仍然必须重新散列索引）。所以，仍然坚持使用 awk：
#!/usr/bin/awk -f
BEGIN { cl=1; }
/foo5/ {
for (i=cl; i<cl+N; i++)
print pLines[i % N];
cl=1;
}
{ pLines[cl % N] = $0; cl = cl + 1; }
cl 代表当前行。如果我们有匹配项，我们将打印之前存储在 pLines 数组中的 N 行。您可能希望打印图案本身，但我没有。无论看到模式如何，我们都会使用 % 运算符将刚刚处理的行存储在 pLines 中，因此我们不必移动数组。
为了
zoo0
blah1
foo2
bar3
hehe4
lisp5
foo5
blah6
foo7
bar8
hehe9
foo5
此打印
blah1
foo2
bar3
hehe4
lisp5
foo5
blah6
foo7
bar8
hehe9
这是不包括模式的前 5 行。
它也可以合理地工作
hehe4
lisp5
foo5
blah6
foo7
bar8
hehe9
foo5
在 foo5 的第一个匹配之前没有前 5 行。在这种情况下，它打印空行。您可能需要根据您的需求进行定制。
哎哟！
这是 Perl 中的解决方案。 因为这些行是“比赛之前”的，所以您必须使用缓冲区。 我包含了一个 $bufferSize 命令行参数。 名为 @buffer 的数组将始终包含最后 $bufferSize 行。 当找到匹配项时，打印末尾包含匹配行的缓冲区。 这是代码。 我在 Larry Wall 编写的《Programming Perl》文本文件上运行了这个。
#!/usr/bin/perl -w
=begin
#usage perl thisFile.pl bufferSize inputFile
#print n lines before match. Because it is BEFORE the match, you will
need to use a buffer. I have limited the buffer to just the given
bufferSize, but you could store the entire file in a buffer if need be.
=end
=cut
my $bufferSize = shift; #grab buffer size from command line arguments
my @buffer;
while(<>){
push(@buffer, "$_"); #store current line in buffer to be accessed when a match is found
if($#buffer > $bufferSize){ shift(@buffer); } #if the buffer is bigger than $bufferSize, remove a line from the beginning of the array with shift, pop removes from the end of the array
if(/diamond/i){ #match found, print buffer
print "\n\n***Match Found: Line $.***\n";
my $i=1;
for(@buffer){print "$i\t: $_"; $i++;}
}
}
输出看起来像这样
$ perl print.n.lines.before.match.pl 15 programming.perl.txt
***Match Found: Line 25975***
1 : stalled on the target system. (It might need some shared libraries, though, if you
2 : didn’t link everything statically.) However, this program isn’t really any different
3 : than the regular Perl interpreter that runs your script. It’s just precompiled into
4 : a standalone executable image.
5 : The B::CC module, however, tries to do more than that. The beginning of the C
6 : source file it generates looks pretty much like what B::C produced5 but, eventu-
7 : ally, any similarity ends. In the B::C code, you have a big opcode table in C that’s
8 : manipulated just as the interpreter would do on its own, whereas the C code
9 : generated by B::CC is laid out in the order corresponding to the runtime flow of
10 : your program. It even has a C function corresponding to each function in your
11 : program. Some amount of optimization based on variable types is done; a few
12 : benchmarks can run twice as fast as in the standard interpreter. This is the most
13 : ambitious of the current code generators, the one that holds the greatest promise
14 : for the future. By no coincidence, it is also the least stable of the three.
15 : Computer science students looking for graduate thesis projects need look no fur-
16 : ther. There are plenty of diamonds in the rough waiting to be polished off here.
这里有一个解决方案，可以在此处类似的问题中找到匹配后的 n 行。匹配模式后打印特定行数
#!/usr/bin/perl -w
#usage perl thisFile.pl bufferSize inputFile
#print n lines after match
$n = shift;
while(<>){
if( /diamond/i ){
print "\n\n***Match found: Line $.***\n$_"; #print header and matching line
#print next 81 lines
for( 1 .. $n ){
print "$_:\t" . <>;
}
}
}
输出看起来像这样
$ perl print.n.lines.after.match.pl 15 programming.perl.txt
***Match found: Line 25975***
0: ther. There are plenty of diamonds in the rough waiting to be polished off here.
1:
2:
3: Code Development Tools
4: The O module has many interesting Modi Operandi beyond feeding the exasper-
5: atingly experimental code generators. By providing relatively painless access to
6: the Perl compiler’s output, this module makes it easy to build other tools that
7: need to know everything about a Perl program.
8: The B::Lint module is named after lint(1), the C program verifier. It inspects
9: programs for questionable constructs that often trip up beginners but don’t nor-
10: mally trigger warnings. Call the module directly:
11: % perl –MO=Lint,all myprog
12:
13:
14:
15:
祝你好运！