shell script for extracting out the shortest substring from the given starting and en - Shell Programming and Scripting

pankajd · #1 (**permalink**) 10-18-2007

hi all,
i need an urgent help for writing a shell script which will extract out and print a substring which is the shortest substring from the given string where first and last character of that substring will be given by the user.
for e.g.
if str="abcdpqracdpqaserd"
now if the user gives 'a' and 'd' as the first and last character of the substringi.e. command line arguments.this should extract out acd as the shortest string.
please give simple solution to this.

ghostdog74 · #2 (**permalink**) 10-19-2007

Code:

str="abcpqracdpqaserd"
startch="a"
endch="d"
awk -v str=$str -v st=$startch -v end=$endch 'BEGIN{ 
s=index(str,startch)
e=index(str,end)
print substr(str,s,e)
}'

output:

Code:

# ./test.sh
abcpqracd

aigles · #3 (**permalink**) 10-19-2007

Another way with sed (first and last can't be special chars) :

Code:

str="abcdpqracdpqaserd"
first=a
last=d
substr=$(echo "$str"| sed -n "s/^[^$first]*\($first[^$last]*$last\).*/\1/p")

Code:

$ sh -x substr.sh
+ str=abcdpqracdpqaserd
+ first=a
+ last=d
++ echo abcdpqracdpqaserd
++ sed 's/^[^a]*\(a[^d]*d\).*/\1/p'
+ substr=abcd
+ echo abcd
abcd
$

Jean-Pierre.

summer_cherry · #4 (**permalink**) 10-19-2007

Hi,

If really took my much efforts. I have tested it for many cases. And they are all ok. Hope this is right on your target.

input:

Code:

abcdpqracdpqaserd
abcdpqracdpqaserd
abcdpqracdpqaserd

output (start:a end:d):

Code:

acd
acd
acd

output (start:a end

):

Code:

acdp
acdp
acdp

output (start:a end:r):

Code:

abcdpqr
abcdpqr
abcdpqr

code:

Code:

read a
read b
sed -e "s/$a[^$b]*$b/|&|/g" a > temp_a
sed 's/^|//' temp_a > temp_b

nawk -v st=$a -v ed=$b 'BEGIN{
FS="|"
}
{
for(i=1;i<=NF;i++)
{
	str=sprintf("b%s",$i)
	if(index(str,"a")==2)
	{
		if(tmp=="")
		{
			tmp=$i
		}
		else
		{
			if (length($i)<length(tmp))
				tmp=$i
		}
	}
}
print tmp
}
' temp_b

radoulov · #5 (**permalink**) 10-19-2007

With GNU Awk:

Code:

awk 'NF>1&&$0=(FS $NF RT){
	if(length<min){
		min=length;rec=$0}
	}END{
print rec
}' FS="$start" RS="$end" min=9^9 filename

Code:

$ cat file
abcdpqracdpqaserd
$ start=a
$ end=d
$ awk 'NF>1&&$0=(FS $NF RT){
if(length<min){
min=length;rec=$0}
}END{
print rec
}' FS="$start" RS="$end" min=9^9 file
acd
$ start=a
$ end=p
$ awk 'NF>1&&$0=(FS $NF RT){
if(length<min){
min=length;rec=$0}
}END{
print rec
}' FS="$start" RS="$end" min=9^9 file
acdp
$ start=a
$ end=r
$ awk 'NF>1&&$0=(FS $NF RT){
if(length<min){
min=length;rec=$0}
}END{
print rec
}' FS="$start" RS="$end" min=9^9 file
aser

drl · #6 (**permalink**) 10-19-2007

Hi.

I like the solution from aigles. I don't see one yet on perl.

The perl RE syntax has special features for the shortest match. Here is the entire code, along with diagnostic code, minimal argument processing, etc:

Code:

#!/usr/bin/perl

# @(#) p1       Demonstrate non-greedy matching perl RE syntax.

use warnings;
use strict;

my ($debug);
$debug = 0;
$debug = 1;

my ($lines) = 0;

my ($usage) = "usage: $0 first last\n";
my ($first) = shift || die "$usage";
my ($last)  = shift || die "$usage";

my ($string);

while (<>) {
  print " Bounds on this search: $first, $last\n" unless $lines;
  $lines++;
  chomp;
  print "\n";
  print " Initial string = \"$_\"\n";
  if (/($first.*?$last)/) {
    $string = $1;
    print " Shortest substring = \"$string\"\n";
  }
  else {
    print STDERR " No substring found, continuing.\n";
  }
}

print STDERR " ( Lines read: $lines )\n";

exit(0);

Running this on your test line and a few others in file data1:

Code:

% ./p1 a d data1
 Bounds on this search: a, d

 Initial string = "abcdpqracdpqaserd"
 Shortest substring = "abcd"

 Initial string = "abc"
 No substring found, continuing.

 Initial string = "abcdddd"
 Shortest substring = "abcd"
 ( Lines read: 3 )

The heart of the match is in these characters .*?

See the man pages for:

Code:

perlre              Perl regular expressions, the rest of the story
perlreref           Perl regular expressions quick reference

for details ... cheers, drl

radoulov · #7 (**permalink**) 10-19-2007

Am I missing something, or the OP wanted acd (not abcd)from abcdpqracdpqaserd with a and d?

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