grep lines before and after in aix/ksh shell - linux

Question

I want to extract lines before and after a matched pattern.
eg: if the file contents are as follows
absbasdakjkglksagjgj
sajlkgsgjlskjlasj
hello
lkgjkdsfjlkjsgklks
klgdsgklsdgkldskgdsg
I need find hello and display line before and after 'hello'
the output should be
sajlkgsgjlskjlasj
hello
lkgjkdsfjlkjsgklks
This is possible with GNU but i need a method that works in AIX / KSH SHELL WHERE NO GNU IS INSTALLED.

Answer 1

sed -n '/hello/{x;G;N;p;};h' filename

Answer 2

I've found it is generally less frustrating to build the GNU coreutils once, and benefit from many more features http://www.gnu.org/software/coreutils/

Answer 3

Since you'll have Perl on the machine, you could use the following code, but you'd probably do better to install the GNU utilities. This has options -b n1 for lines before and -f n1 for lines following the match. It works with PCRE matches (so if you want case-insensitive matching, add an i after the regex instead using a -i option. I haven't implemented -v or -l; I didn't need those.
#!/usr/bin/env perl
#
# #(#)$Id: sgrep.pl,v 1.7 2013/01/28 02:07:18 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 warnings;
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 = ();
}
}

Answer 4

I had a situation where I was stuck with a slow telnet session on a tablet, believe it or not, and I couldn't write a Perl script very easily with that keyboard. I came up with this hacky maneuver that worked in a pinch for me with AIX's limited grep. This won't work well if your grep returns hundreds of lines, but if you just need one line and one or two above/below it, this could do it. First I ran this:
cat -n filename |grep criteria
By including the -n flag, I see the line number of the data I'm seeking, like this:
2543 my crucial data
Since cat gives the line number 2 spaces before and 1 space after, I could grep for the line number right before it like this:
cat -n filename |grep " 2542 "
I ran this a couple of times to give me lines 2542 and 2544 that bookended line 2543. Like I said, it's definitely fallable, like if you have reams of data that might have " 2542 " all over the place, but just to grab a couple of quick lines, it worked well.