How can I use the output of ls/grep as input for pdfunite

Question

I want to use pdfunite to merge several pdf-files into one output file. Since the directory contains lots of different stuff, I thought i could use ls/grep to get the apropriate file-names and then use pdfunite to get it put together. The output of ls/grep look like this:

ls | grep "handout...pdf" 
handout01.pdf*
handout02.pdf*
handout03.pdf*
handout04.pdf*
handout05.pdf*
handout06.pdf*

Then I want to invoke pdfunit, which has the following syntax:

 pdfunite [options] PDF-sourcefile1..PDF-sourcefilen PDF-destfile

My Problem is, that it does not seem like I can pipe the output of ls/grep into pdfunite, because it is not supposed to work like that. On the otherhand, if I try:

pdfunite ls | grep "handout...pdf" grep.pdf

then grep obviously complains about my chosen output-file:

grep: grep.pdf: No such file or directory

I know I could do two seperate steps and then it would work, but I'd like to figure out how to do this with one line.

Answer 1

If your file patterns are that simple, you don't really need a regex, and you can use a simple wildcard:

pdfunite handout??.pdf

Otherwise, you can use a regex with the find command and -regex, but I could not find a way to execute it that doesn't have the possibility of splitting up into multiple groups of files. Some of the ways you might do it also depend on none of the filenames having any spaces in them.

Answer 2

the "tick" character can be used to do that (the thing above the tilda), I believe. Try something like this:

pdfunite [options] `ls | grep "handout...pdf"`

From what I understand, that's how you nest a command. Anything inside the ticks is executed as its own command, and the output of it replaces the ticks. So, the command above would essentially equate to

pdfunite [options] handout01.pdf* handout02.pdf* ...

Answer 3

You don't necessarily need a grep. You can pass on the pattern to ls.

pdfunite $(ls handout*.pdf*) merged.pdf