我正在使用UNIX系统，并尝试运行一个应用程序，该程序将一些调试日志输出到标准输出。我已经将此输出重定向到日志文件，但现在希望获取显示错误的行。
我的问题在于简单的
cat output.log | grep FAIL
这并没有帮助我。因为它只显示了那些包含“FAIL”字样的行。我想要更多的信息，比如包括在这个行上方2-3行的内容。有没有办法通过一个简单的shell命令实现这个功能？我希望只用一条命令（可以使用管道）就能够完成上述操作。
5个回答
5
grep -A $NUM
这将在匹配后打印$NUM行尾部上下文。
-B $NUM会打印前导上下文。
man grep是你最好的朋友。
因此，在您的情况下：
cat log | grep -A 3 -B 3 FAIL
- MikeReedell
1
与GNU grep相配合运行效果良好；不是标准（POSIX，Unix）grep的一部分。 - Jonathan Leffler
3
http://thedailywtf.com/Articles/The_Complicator_0x27_s_Gloves.aspx
你可以使用sed打印特定行，比如你想要第20行：
sed '20 p' -n FILE_YOU_WANT_THE_LINE_FROM完成。
-n 防止从文件中回显行。引号中的部分是要应用的
sed规则，它指定你希望该规则应用于第20行，并且你希望打印。- Bryan
3
我有两个实现我称之为“sgrep”的程序，一个是Perl的，另一个使用仅使用pre-Perl（pre-GNU）标准Unix命令。如果您有GNU grep，则没有特别需要这些程序。处理正向和反向环境搜索可能更加复杂，但这可能是一个有用的练习。
Perl解决方案：
Perl解决方案：
#!/usr/perl/v5.8.8/bin/perl -w
#
# @(#)$Id: sgrep.pl,v 1.6 2007/09/18 22:55:20 jleffler Exp $
#
# Perl-based SGREP (special grep) command
#
# Print lines around the line that matches (by default, 3 before and 3 after).
# By default, include file names if more than one file to search.
#
# Options:
# -b n1 Print n1 lines before match
# -f n2 Print n2 lines following match
# -n Print line numbers
# -h Do not print file names
# -H Do print file names
use strict;
use constant debug => 0;
use Getopt::Std;
my(%opts);
sub usage
{
print STDERR "Usage: $0 [-hnH] [-b n1] [-f n2] pattern [file ...]\n";
exit 1;
}
usage unless getopts('hnf:b:H', \%opts);
usage unless @ARGV >= 1;
if ($opts{h} && $opts{H})
{
print STDERR "$0: mutually exclusive options -h and -H specified\n";
exit 1;
}
my $op = shift;
print "# regex = $op\n" if debug;
# print file names if -h omitted and more than one argument
$opts{F} = (defined $opts{H} || (!defined $opts{h} and scalar @ARGV > 1)) ? 1 : 0;
$opts{n} = 0 unless defined $opts{n};
my $before = (defined $opts{b}) ? $opts{b} + 0 : 3;
my $after = (defined $opts{f}) ? $opts{f} + 0 : 3;
print "# before = $before; after = $after\n" if debug;
my @lines = (); # Accumulated lines
my $tail = 0; # Line number of last line in list
my $tbp_1 = 0; # First line to be printed
my $tbp_2 = 0; # Last line to be printed
# Print lines from @lines in the range $tbp_1 .. $tbp_2,
# leaving $leave lines in the array for future use.
sub print_leaving
{
my ($leave) = @_;
while (scalar(@lines) > $leave)
{
my $line = shift @lines;
my $curr = $tail - scalar(@lines);
if ($tbp_1 <= $curr && $curr <= $tbp_2)
{
print "$ARGV:" if $opts{F};
print "$curr:" if $opts{n};
print $line;
}
}
}
# General logic:
# Accumulate each line at end of @lines.
# ** If current line matches, record range that needs printing
# ** When the line array contains enough lines, pop line off front and,
# if it needs printing, print it.
# At end of file, empty line array, printing requisite accumulated lines.
while (<>)
{
# Add this line to the accumulated lines
push @lines, $_;
$tail = $.;
printf "# array: N = %d, last = $tail: %s", scalar(@lines), $_ if debug > 1;
if (m/$op/o)
{
# This line matches - set range to be printed
my $lo = $. - $before;
$tbp_1 = $lo if ($lo > $tbp_2);
$tbp_2 = $. + $after;
print "# $. MATCH: print range $tbp_1 .. $tbp_2\n" if debug;
}
# Print out any accumulated lines that need printing
# Leave $before lines in array.
print_leaving($before);
}
continue
{
if (eof)
{
# Print out any accumulated lines that need printing
print_leaving(0);
# Reset for next file
close ARGV;
$tbp_1 = 0;
$tbp_2 = 0;
$tail = 0;
@lines = ();
}
}
在Perl出现之前的Unix解决方案（使用纯文本编辑器ed，sed和sort - 虽然它使用了getopt，但那时可能还没有这个命令）：
#!/bin/ksh
#
# @(#)$Id: old.sgrep.sh,v 1.5 2007/09/15 22:15:43 jleffler Exp $
#
# Special grep
# Finds a pattern and prints lines either side of the pattern
# Line numbers are always produced by ed (substitute for grep),
# which allows us to eliminate duplicate lines cleanly. If the
# user did not ask for numbers, these are then stripped out.
#
# BUG: if the pattern occurs in in the first line or two and
# the number of lines to go back is larger than the line number,
# it fails dismally.
set -- `getopt "f:b:hn" "$@"`
case $# in
0) echo "Usage: $0 [-hn] [-f x] [-b y] pattern [files]" >&2
exit 1;;
esac
# Tab required - at least with sed (perl would be different)
# But then the whole problem would be different if implemented in Perl.
number="'s/^\\([0-9][0-9]*\\) /\\1:/'"
filename="'s%^%%'" # No-op for sed
f=3
b=3
nflag=no
hflag=no
while [ $# -gt 0 ]
do
case $1 in
-f) f=$2; shift 2;;
-b) b=$2; shift 2;;
-n) nflag=yes; shift;;
-h) hflag=yes; shift;;
--) shift; break;;
*) echo "Unknown option $1" >&2
exit 1;;
esac
done
pattern="${1:?'No pattern'}"
shift
case $# in
0) tmp=${TMPDIR:-/tmp}/`basename $0`.$$
trap "rm -f $tmp ; exit 1" 0
cat - >$tmp
set -- $tmp
sort="sort -t: -u +0n -1"
;;
*) filename="'s%^%'\$file:%"
sort="sort -t: -u +1n -2"
;;
esac
case $nflag in
yes) num_remove='s/[0-9][0-9]*://';;
no) num_remove='s/^//';;
esac
case $hflag in
yes) fileremove='s%^$file:%%';;
no) fileremove='s/^//';;
esac
for file in $*
do
echo "g/$pattern/.-${b},.+${f}n" |
ed - $file |
eval sed -e "$number" -e "$filename" |
$sort |
eval sed -e "$fileremove" -e "$num_remove"
done
rm -f $tmp
trap 0
exit 0
sgrep的Shell版本是在1989年2月编写的，并在同年5月进行了错误修复。从1997年开始，除了行政变更（从SCCS到RCS）外，它一直没有改变，直到2007年我添加了-h选项。我在2007年转换为Perl版本。
- Jonathan Leffler
1
$ grep --context 3 FAIL output.log
$ grep --help | grep context
-B, --before-context=NUM 打印前 NUM 行上下文 -A, --after-context=NUM 打印后 NUM 行上下文 -C, --context=NUM 打印 NUM 行输出上下文 -NUM 等同于 --context=NUM
- J.F. Sebastian
1
顺便说一句，我确实知道这个问题有标签“unix”，我只是在Windows上测试了它。 - jfs
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