Shell Programming and Scripting

$ cat infile
HEADER474687
D1356jkl ugbliuybikb 879870
898976098 9687680
D77656757 uhgliug liygoiygig
D98679hjh kjbgihguygfu ugliyh
kbygfluy9809
D8796870 kjlhuigiyig
TRAILER0008
$ cat script.pl
use warnings;
use strict;

die qq[Usage: perl $0 <input-file>\n] unless @ARGV == 1;

my @lines;

while ( <> ) {
        chomp;

        ## First line: Print and read next.
        if ( $. == 1 ) {
                printf qq[%s\n], $_;
                next;
        }

        ## Lines beginning with 'D': Remove previous saved lines from
        ## array to print them and save current line.
        if ( m/\AD/ ) {
                if ( @lines ) {
                        printf qq[%s\n], join qq[ ], splice @lines, 0;
                }
                push @lines, $_;
                next;
        }

        ## Last line: Print saved lines plus current one.
        if ( eof ) {
                printf qq[%s\n%s\n], join( qq[ ], splice( @lines, 0 ) ), $_;
                next;
        }

        ## Lines NOT beginning with 'D': Save them in array to print them
        ## later.
        push @lines, $_;
}
$ perl script.pl infile
HEADER474687
D1356jkl ugbliuybikb 879870 898976098 9687680
D77656757 uhgliug liygoiygig
D98679hjh kjbgihguygfu ugliyh kbygfluy9809
D8796870 kjlhuigiyig
TRAILER0008

awk '{
if(NR == 1)
print $0;
else if(NR != 1) 
{
if($0 !~ /^TRAILER/)
{
if($0 ~ /^D/)
{
printf "%s\n", $0 ; next 
}
else
{
}
}
else
{
last=$0;
}
}
}
END {
print last;
}' f5

HEADER474687
D1356jkl ugbliuybikb 879870
898976098 9687680
D77656757 uhgliug liygoiygig
D98679hjh kjbgihguygfu ugliyh
kbygfluy9809
D8796870 kjlhuigiyig
TRAILER0008

HEADER474687
D1356jkl ugbliuybikb 879870 898976098 9687680
D77656757 uhgliug liygoiygig
D98679hjh kjbgihguygfu ugliyh kbygfluy9809
D8796870 kjlhuigiyig
TRAILER0008

HEADER474687
D1356jkl ugbliuybikb 879870
D77656757 uhgliug liygoiygig
D98679hjh kjbgihguygfu ugliyh
D8796870 kjlhuigiyig
TRAILER0008

awk '
NR==1{print}  
/^TRAILER/{if(a) print a; print ; exit} 
NR>1 && !/^D/{print a" "$0; a=""}
/^D/{ if(a) print a; a=$0 }' infile

$ cat script.sed
1 { 
        p
        b
}

/^D/ {
        x
        s/^\n//
        s/\n/ /g
        /./ p
        b
}

/^D/! {
        $! {
                H
                b
        }
}

$ {
        H
        x
        s/^\n//
        p
}
$ sed -n -f script.sed infile
HEADER474687
D1356jkl ugbliuybikb 879870 898976098 9687680
D77656757 uhgliug liygoiygig
D98679hjh kjbgihguygfu ugliyh kbygfluy9809
D8796870 kjlhuigiyig
TRAILER0008

# sed -n -f script.sed temp.txt
Unrecognized command: /^D/! {