Combining two pdfs with pdftk and the use of a loop

Question

I have been working a project that involves combining the pages of two pdfs in a way that the pages from one pdf are the even pages of the final pdf and the pages of the second pdf are the odd pages of the final pdf, So for example say I have odd.pdf and even.pdf I want the final.pdf to have the form: odd(page1)even(page2)odd(page2)even(page2). This is my idea so far:

A=odd.pdf

B=even.pdf

sum=sum(even.pdf,odd.pdf)

for i in $(seq 1 $sum);

do

    pdftk A=even.pdf B=odd.pdf cat B($i) A($i)

done

output output.pdf

The main issue I have is that I cant find a way to get the sum of two pdf files' pages and then again I am not so proficient with pdftk and I dont know if the program will work as intended(or if it will work at all! :P) Thanks a lot!

• I am also not so proficient with Bash (mostly a python guy) so any improvements-tips will also be really helpfull!

Answer 1

If I'm understanding your requirement correctly, would you please try:

pdftk A=odd.pdf B=even.pdf shuffle A B output final.pdf

Then the final.pdf will have interleaved pages such as:

odd.pdf     1     2     3  ..
even.pdf       1     2     3  ..
--------------------------------
final.pdf   1  2  3  4  5  6  ..

[Edit]
As the cat command of pdftk is not indended to be used in the loop, we need to use some tricks:

#!/bin/bash

# caclurate the page counts of the two files
pagesA=$(pdftk odd.pdf dump_data | awk '/NumberOfPages/ {print $2}')
pagesB=$(pdftk even.pdf dump_data | awk '/NumberOfPages/ {print $2}')

# determine which file has more pages
if (( pagesA < pagesB )); then
    min=$pagesA
    max=$pagesB
    remainder=even.pdf
else
    min=$pagesB
    max=$pagesA
    remainder=odd.pdf
fi

# at first, append the 1st pages
pdftk A=odd.pdf B=even.pdf cat A1 B1 output output.pdf

# append pages up to the common last pages
for (( i = 2; i <= min; i++ )); do
    pdftk A=odd.pdf B=even.pdf C=output.pdf cat C A"$i" B"$i" output tmp.pdf
    mv -f tmp.pdf output.pdf
done

# append remaining pages
for (( i = min+1; i <= max; i++ )); do
    pdftk A=$remainder C=output.pdf cat C A"$i" output tmp.pdf
    mv -f tmp.pdf output.pdf
done

It first merges the first pages to generate the initial pdf file as an "appendee" then append the remaining pages in the next loop by renaming the output file each time.

If you are not forced to use the pdftk command within the loop, here is an alternative which will be faster and more efficient:

#!/bin/bash

# caclurate the page counts of the two files
pagesA=$(pdftk odd.pdf dump_data | awk '/NumberOfPages/ {print $2}')
pagesB=$(pdftk even.pdf dump_data | awk '/NumberOfPages/ {print $2}')

# determine which file has more pages
if (( pagesA < pagesB )); then
    min=$pagesA
    max=$pagesB
    remainder="B"
else
    min=$pagesB
    max=$pagesA
    remainder="A"
fi

# generate a list of pages up to the common last page
for (( i = 1; i <= min; i++ )); do
    pages+=(A"$i" B"$i")
done

# append a list of remaining pages
for (( i = min+1; i <= max; i++ )); do
    pages+=("$remainder$i")
done

pdftk A=odd.pdf B=even.pdf cat "${pages[@]}" output output.pdf

You'll see how the list is expanded by putting echo command in front of the pdftk command.