$ cat file
START
Unix
Linux
START
Solaris
Aix
SCO 1. Join the lines following the pattern START without any delimiter.
$ awk '/START/{if (NR!=1)print "";next}{printf $0}END{print "";}' file
UnixLinux
SolarisAixSCO
2. Join the lines following the pattern START with space as delimiter.
$ awk '/START/{if (NR!=1)print "";next}{printf "%s ",$0}END{print "";}' file
Unix Linux
Solaris Aix SCO
3. Join the lines following the pattern START with comma as delimiter.
$ awk '/START/{if (x)print x;x="";next}{x=(!x)?$0:x","$0;}END{print x;}' file
Unix,Linux
Solaris,Aix,SCO
4. Join the lines following the pattern START with comma as delimiter with also the pattern matching line.
$ awk '/START/{if (x)print x;x="";}{x=(!x)?$0:x","$0;}END{print x;}' file
START,Unix,Linux
START,Solaris,Aix,SCO
5. Join the lines following the pattern START with comma as delimiter with also the pattern matching line. However, the pattern line should not be joined.
$ awk '/START/{if (x)print x;print;x="";next}{x=(!x)?$0:x","$0;}END{print x;}' file
START
Unix,Linux
START
Solaris,Aix,SCO
6. Other ways:
paste -d, -s file
cat file | xargsREF:
http://www.theunixschool.com/2012/05/awk-join-or-merge-lines-on-finding.html
https://*.com/questions/15758814/turning-multiple-lines-into-one-line-with-comma-separated-perl-sed-awk
==========================================================
AC M07451
ID V$PBX1_10
NA PBX1
AC M07452
ID V$MEIS1_06
NA Meis1
AC M07453
ID V$MEIS1BHOXA9PBX1A_01
NA Meis1b:Hoxa9:Pbx1a
AC M07454
ID V$GLI1_Q3_01
NA Gli1
AC M07455
ID V$GLI2_Q3
NA Gli2
AC M07456
ID V$HOXA913_Q4
NA HOX 9-13
awk '$0 ~ /^AC|^ID|^NA/' conserved.new \
| awk '/AC /{if (x)print x;x="";}{x=(!x)?$0:x","$0;}END{print x;}' \
| sed 's/AC //g' | sed 's/,ID /\t/g' | sed 's/,NA /\t/g' \
> genesymbol
M07451 V$PBX1_10 PBX1
M07452 V$MEIS1_06 Meis1
M07453 V$MEIS1BHOXA9PBX1A_01 Meis1b:Hoxa9:Pbx1a
M07454 V$GLI1_Q3_01 Gli1
M07455 V$GLI2_Q3 Gli2
==========================================================
more file
start111
aa
bb
cc
start222
dd
ee
awk '/start/{if (x)print x;x="";}{x=(!x)?$0:x","$0;}END{print x;}' file > bbb
more bbb
start111,aa,bb,cc
start222,dd,ee
awk -F"[|, ]" '{for(i=2;i<=NF;i++){print $1"|"$i}}' bbb
start111|aa
start111|bb
start111|cc
start222|dd
start222|ee