mergePdfs.sh

#!/bin/bash

# 54321_xxxxxx_yyyyy.pdf
# 54321_xxxxxx_yyyyy.pdf
# 54321_xxxxxx_yyyyy.pdf
# will become 54321.pdf

# 54322_xxxxxx_yyyyy.pdf
# 54322_xxxxxx_yyyyy.pdf
# will become 54322.pdf

cd /mnt/c/TEMP/pdfs

list="";

for file in *pdf; do
        if [ -f "$file" ]; then
                #echo "$file"
                num="${file:0:5}"
                list="$list $num"
        fi
done

#echo $list

uniques=$(echo $list | tr ' ' '\n' | sort -nu)

#echo $uniques

for uni in $uniques; do
        echo "Creating $uni ..."
        pdfunite $(echo "$uni"_*) "merged/$uni.pdf"
done