Shell Programming and Scripting

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)
}'

# ./test.sh
abcpqracd

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

$ 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
$

abcdpqracdpqaserd
abcdpqracdpqaserd
abcdpqracdpqaserd

acd
acd
acd

acdp
acdp
acdp

abcdpqr
abcdpqr
abcdpqr

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

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

$ 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

#!/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);

% ./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 )

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