UNIX for Beginners Questions & Answers

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 Sometxt
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 watch this space for tools 
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 \Start\then\go language again
 cubernates space 
 sign in done 
 line again
 do it now

\Start

 \Start\now\fine stepwatch this space for toolsends here 
 \Start\then\go language againcubernates spacesign in doneline againdo itnow

 sed -n '^//Start/{
 s/[ \t]*$// # trim trailing spaces
 N # Move to next line
 s/\n//p #join line and print them

sed -i 's/[ \t]*$//g' f1.txt ; gawk '/^\\Start/{gsub("[\n]","",$0);print $0}RS=""' f1.txt

\Start\then\go language againcubernates spacesign in doneline againdo itnow

awk '/\\Start/{f=1};!NF{if (f) print A[f];split("",A);f=0};{gsub(/^ /,"");A[f]=A[f]?A[f] $0:$0};END{if (f) print A[f]}'

awk '/\\Start/{f=1} !NF{if(f)print s; s=x; f=0} f{s=s $0} END{if(f) print s}'  file

 \Start\now\fine step watch this space for tools  ends here 
 \Start\then\go language again cubernates space  sign in done  line again do it now

awk 'NF{$1=$1} /^\\Start/{f=1} !NF{if(f)print s; s=x; f=0} f{s=s $0} END{if(f) print s}'

\Start\now\fine stepwatch this space for toolsends here
\Start\then\go language againcubernates spacesign in doneline againdo it now

!NF{if(f)print s; s=x; f=0}

awk '/Start/,/^$/ {action}

Solved AWK/Sed Join

sed -rn 's/^ *| *$//; / *\\Start/,/^$/ {H; /^$/ {g;s/\n//g;p;s/.*//;h; };}; $ {g;s/\n//g;p;}' file
\Start\now\fine stepwatch this space for tools ends here 
\Start\then\go language againcubernates space sign in done line againdo it now