Useful tools and commands

Andreas Windisch

This repo serves as a place where I collect commands that I find useful. Since I do not use those commands on a daily basis, I intend to collect some of them here, so I don't have to browse the net to track them down in times of need. Feel free to add your personal favorite commands by opening new sections in this document. You can also find and connect with me on LinkedIn.
Cheers, Andreas.

PDFs and GhostScript

Splitting PDFs with pdftk

Sometimes it is convenient to split up a pdf into individual pages. This can easily be achieved by using pdftk.

pdftk input.pdf burst output page_%02d.pdf

Alternatively, one can also isolate particular pages. For example, to extract the 4th page of a pdf one can use:

pdftk input.pdf cat 4 output output.pdf

Instead of cat 4 one can also specify several pages or ranges, like 1-4 for pages 1 through 4.

Ghost Script is also really nice for dealing with PDFs. Here are two applications that I frequently encounter, and both can be addressed nicely using gs.

Merging PDFs with gs

In order to merge several PDFs into one output file, use:

gs -dNOPAUSE -sDEVICE=pdfwrite -sOUTPUTFILE=output.pdf -dBATCH input1.pdf input2.pdf

Sometimes you want to merge PDFs of different format, like landscape vs. portrait, or slightly larger slides with slightly smaller slides. Here, the following command solved the problem for me, where I used pdfjoin rather than ghostscript.

pdfjoin --paper a4paper --rotateoversize false input1.pdf input2.pdf

Note that there is no need to specify an output filename, as it is chosen by the program.

Rasterizing PDFs into PNGs using gs

This is another useful command to rasterize large PDFs (for example, 3d-plots produced with Wolfram Mathematica) into PNGs. The rasterization can be done with a very high resolution, and the resulting size of the PNGs will still be reasonably small. To rasterize the image, use:

gs -sDEVICE=png16m -dTextAlphaBits=4 -r300 -o output.png input.pdf

Compressing PDFs with ghostscript

Sometimes it is necessary to compress pdf files. This can also be done with ghost script. Note that in some cases a particular approach can lead to an increase in file size. That happend to me as well in a particular case, and I had to try various different suggestions till I found one that worked. Here is an example that worked for me:

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf

The quality setting (and thus the rate of compression) in this case is controlled via the -dPDFSETTINGS switch, see this blog post. According to this post, the following settings are available.

Setting	quality
/screen	low
/ebook	moderate
/printer	good
/prepress	high

Here is another command that increased the file size in the case where the above command was successful, but it may work in other cases.

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/default -dNOPAUSE -dQUIET -dBATCH -dDetectDuplicateImages -dCompressFonts=true -r150 -sOutputFile=output.pdf input.pdf

Feel free to add your own commands here or send them per email to andreas.windisch@yahoo.com so I can add them for you, in case you prefer that.

Using (non-WiFi) HP network scanner with linux command line

I have a HP all-in-one network scanner/printer (Photosmart C5100) that I use in combination with the command line tool scanimage. For the printer side I just used the webinterface of CUPS to set up the printer. In order to use the network scanner from the command line you have to set it up first.

#you need to install hplip for your distribution, then run:
hp-setup

Running this command positively identified the device on my network. Now make sure that scanimage recognizes the device.

scanimage -L
#output:
#device `hpaio:/net/Photosmart_C5100_series?ip=XXX.XXX.XXX.XXX' is a Hewlett-Packard Photosmart_C5100_series all-in-one

Note: It could happen, that if the IP address of the scanner/printer changes over time, that you can't reach the scanner/printer on the network. In that case, just remove the device with the outdated IP address using the command

hp-setup -r

Now you can scan directly from the command line. For example, I had to scan a nasty logbook with many pages and I intended to combine everything in a PDF afterwards. Here is what I did.

#STEP 1: scan page by page to working directory (cd into wd first)
scanimage --resolution 200 > page000.jpg
scanimage --resolution 200 > page001.jpg
...
scanimage --resolution 200 > page110.jpg

Now use convert to arrange all the jpgs in one PDF:

#STEP 2: Build PDF from jpgs
convert *.jpg all_pages.pdf

Finally compress the PDF to a reasonable size using ghost script, see also the PDF compression section of this document.

#STEP 3: compress PDF
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH -sOutputFile=all_pages_compressed.pdf all_pages.pdf

ffmpeg and imagemagick

Conversion of avi to mp4:

ffmpeg -i movie1.avi -sameq movie1.mp4

ffmpeg -i movie1.avi -qscale 0 movie1.mp4

ffmpeg -i movie1.avi -vcodec libx264 movie1.mp4

ffmpeg -i movie1.avi -vcodec msmpeg4v2 -acodec copy movie1_compressed.avi 

Create movie from pngs. The filename convention here is: pic_00.png, pic_01.png, .....

ffmpeg -framerate 10 -i pic_%02d.png -s:v 800x600 -c:v libx264 -profile:v high -pix_fmt yuv420p movie.mp4

Split animated gif into pngs:

convert animated.gif pic_%03d.png

Merge pngs into animated gif:

convert -delay 0.1 -loop 0 *.png animated.gif

Compress a mp4 movie:

ffmpeg -i input.mp4 -vcodec h264 -acodec mp3 output.mp4

Create an animated gif from a mp4 movie (with downscaling and time):

ffmpeg -i input.mp4 -r 25 -vf scale=512:-1 -ss 00:00:00 -to 00:00:16 output.gif

Convert from Matroska format to mp4:

ffmpeg -i input.mkv -codec copy output.mp4