The following is not the proper way to modularize your code, but because you are just 'one yard before the finish line' you could use a script or Makefile to concatenate multiple files to a single program. That is easier and less error prone then the temporary "manually cut and paste" solution, that you are considering.

Assuming you have the following files:

-rw-r--r--  1 hadri  hadri   51 Feb 12 04:24 main_barack
-rw-r--r--  1 hadri  hadri   63 Feb 12 04:15 my-serial-library.src
-rw-r--r--  1 hadri  hadri   68 Feb 12 04:27 postlude_general.src
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Your general libary routines are in my-serial-library.src and postlude_general.src. The 'main' program is the only customized part and is named after your client or location: main_barack.

With a simple Makefile you can generate your program serial_com_barak.pl:

$ make
cat my-serial-library.src main_barack postlude_general.src > serial_co
+mm_barack.pl
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For another customer you create a new customized main and run 'make' again:

$ echo "This is for Bernie" > main_bernie

$ make CLIENT=bernie
cat my-serial-library.src main_bernie postlude_general.src > serial_co
+mm_bernie.pl
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The Makefile:

 # -- sample Makefile
CLIENT          =       barack

NAME            =       serial_comm
PROG_NAME       =       ${NAME}_${CLIENT}.pl

PRELUDE         =       my-serial-library.src
MAIN            =       main_${CLIENT}
POSTLUDE        =       postlude_general.src

TAR_NAME        =       serial-comm_${CLIENT}.tgz
TAR_FILES       =       Makefile
TAR_FILES       +=      ${PRELUDE} ${MAIN} ${POSTLUDE}

${PROG_NAME}: ${PRELUDE} ${MAIN} ${POSTLUDE}  
        cat ${PRELUDE} ${MAIN} ${POSTLUDE} > ${PROG_NAME}

clean:
        rm -rf ${PROG_NAME}

archive:        
        tar cvzf ${TAR_NAME} ${TAR_FILES} 

# --- end of Makefile
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Note: Make sure that you have a tab character (\x09, CNTRL-I or ^I) before the cat and other commands in the Makefile.Verify with 'cat -t Makefile':

${PROG_NAME}: ${PRELUDE} ${MAIN} ${POSTLUDE}  
^Icat ${PRELUDE} ${MAIN} ${POSTLUDE} > ${PROG_NAME}
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