When a Domain is Blocked by Filtering Software
Can’t access your favorite websites because some stupid ISP or access point is using DNS-level filtering?
Set your DNS to use Google’s DNS:
8.8.8.8 and 8.8.4.4
Then flush the existing DNS cache and register the new DNS.
In Windows 7, you’ll need elevated privileges to changes to the DNS. Make sure you start cmd.exe as Administrator.
- Press the window Key
- Type “cmd”
- Right click the cmd.exe that’s found.
- Select “Run as administrator”
- Type
ipconfig /flushdns - Then type
ipconfig /registerdns
Now you’re free to roam the internet.
Get the Directory Path of a Bash Script
So you have a bash script and you want to run it from crontab or some other context where the current working directory isn’t known. Your script wants to use relative path information (from the script itself), perhaps to create a directory structure in the script’s base directory.
The question is: How do you get the directory path of the script? dirname? Not reliably.
#!/bin/bash ABSPATH="$(cd "${0%/*}" 2>/dev/null; echo "$PWD"/"${0##*/}")" CWD=`dirname "$ABSPATH"`
Nice!
Periodic Tarballs: Find and Awk
I have a gang of directories. There’s a new directory each day! Each directory stores about 20k files. Over time, the performance of the directory hierarchy degrades, and it’s best for me to tar up old stuff.
In linux-land, there’s always more than one way of doing things… even if it’s not the right way. Today, we’ll explore find piped to awk piped to the shell.
find . -type d -maxdepth 1 -mtime +60 | sort | awk -F"/" '{print "tar czf " $2 ".tar.gz --remove-files ./" $2 "; rmdir " $2 }' | sh
Basically, find all sub-directories in the current directory — don’t go recursive. Sort for sanity. Extract the file name portion (lots of ways to do this). Generate a shell command tar czf {{dirname}}.tar.gz --remove-files ./{{dirname}}; rmdir {{dirname}} to build the tarball and remove the empty directory when done. Finally, we just tell sh to execute it all… one directory at a time. Bam!
Less-Common Tools for Linux
As found here: 10 Tools to Add Some Spice to Your UNIX Shell Scripts. This is no substitute for the great write-up and screenshots that the author put together. It’s a summary for myself.
The highlights (and how I really feel about them):
- notify-send (I never knew — better than tweat deck)
- tput (eh, maybe)
- setleds (i don’t have lock-key LEDs on my keyboard)
- zenity (has potential)
- kdialog (better than zenity? looks like VB functionality — good?)
- dialog (like kdialog, but uses (n)curses, not kde)
- logger (good to know!)
- setterm (practical jokes… and maybe useful for modal/portal stuff)
- smbclient (does that still work? Couldn’t get past authentication prompt)
- bash sockets (interesting… ICP? wasteful)
PDF to PostScript
Tired of the ghostscript errors? Try poppler (and poppler-utils).
Here’s my problem. I have these PDFs and they are huge! 500MB. The pdf contents is exactly one page, and it’s a scanned image. I want to convert each pdf to a png. When I use ImageMagick’s `convert`, I get this error (followed by a bunch of rubbish):
$ convert 01.pdf 01.ps **** Warning: An error occurred while reading an XREF table. **** The file has been damaged. This may have been caused **** by a problem while converting or transfering the file. **** Ghostscript will attempt to recover the data.
– Enter poppler -
Install poppler-utils (for pdftops)
$ sudo yum install poppler-utils
What do I get when I install poppler-utils? This package contains pdftops (PDF to PostScript converter), pdfinfo (PDF document information extractor), pdfimages (PDF image extractor), pdftohtml (PDF to HTML converter), pdftotext (PDF to text converter), and pdffonts (PDF font analyzer).
packages.debian.org
Let’s look at basic metadata
$ pdfinfo 01.pdf Producer: Adobe Photoshop for Macintosh CreationDate: Fri Mar 12 17:03:08 2010 ModDate: Fri Mar 12 23:12:35 2010 Tagged: no Pages: 1 Encrypted: no Page size: 4114.32 x 3270.72 pts File size: 450186770 bytes Optimized: yes PDF version: 1.7
Now at document-level metadata, including true pixel resolution.
Redundant? Yes, I noticed this too — but look, there’s more!
$ pdfinfo -meta 01.pdf | more Producer: Adobe Photoshop for Macintosh CreationDate: Fri Mar 12 17:03:08 2010 ModDate: Fri Mar 12 23:12:35 2010 Tagged: no Pages: 1 Encrypted: no Page size: 4114.32 x 3270.72 pts File size: 450186770 bytes Optimized: yes PDF version: 1.7 Metadata: <?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?> <x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Adobe XMP Core 4.2.1-c041 52.342996 , 2008/05/07-21:37:19 "> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"> <rdf:Description rdf:about="" xmlns:tiff="http://ns.adobe.com/tiff/1.0/"> <tiff:ImageWidth>17143</tiff:ImageWidth> <tiff:ImageLength>13628</tiff:ImageLength> <tiff:Compression>5</tiff:Compression> <tiff:PhotometricInterpretation>2</tiff:PhotometricInterpretation> <tiff:Orientation>1</tiff:Orientation> <tiff:SamplesPerPixel>3</tiff:SamplesPerPixel> <tiff:PlanarConfiguration>1</tiff:PlanarConfiguration> <tiff:XResolution>3000000/10000</tiff:XResolution> <tiff:YResolution>3000000/10000</tiff:YResolution> <tiff:ResolutionUnit>2</tiff:ResolutionUnit> <tiff:NativeDigest>256,257,258,259,262,274,277,284,530,531,282,283,296, 301,318,319,529,532,306,270,271,272,305,315,33432;B4FF87F3DB26D93C7CFD5C3C5C66BE 9E</tiff:NativeDigest> <tiff:BitsPerSample> <rdf:Seq> <rdf:li>8</rdf:li> <rdf:li>8</rdf:li> <rdf:li>8</rdf:li> </rdf:Seq> </tiff:BitsPerSample> </rdf:Description> ... edited for brevity ...
Look! We found the image dimensions: 17143px by 13628px.
Ok, so why is it that when I run `pdftops` to convert from pdf to ps, followed by ImageMagick’s `convert` from ps to png, I get an image that’s 4114×3270 pixels? I want the full resolution!
Warning, this snippet is incorrect
$ pdftops 01.pdf 01.ps $ convert 01.ps 01.png $ identify 01.png 01.png PNG 4115x3271 4115x3271+0+0 DirectClass 24mb
I must be missing something. … so it is. I overlooked `pdfimages`.
Proper conversion found here
$ pdfimages -j 01.pdf img $ ls 01.pdf img-000.ppm $ identify img-000.ppm img-000.ppm PNM 17143x13628 17143x13628+0+0 DirectClass 6.7e+02mb 4.110u 0:05
Lookie there: full resolution… in a .PPM file? Who cares if ImageMagick can handle it!
From PPM to PNG (like I wanted)
$ convert img-000.ppm img-000.png $ identify img-000.png img-000.png PNG 17143x13628 17143x13628+0+0 DirectClass 3.5e+02mb 12.540u 0:14
And there you have it – Stupid PDF converted to awesome full resolution PNG.
Thank you, come again.
Reference: http://stefaanlippens.net/pdf2ps_vs_pdftops
Recursive directory merge
Problem: I have two directories that are similar in structure but different in content. Say one is an older snapshot of the other. I want to copy the stuff from the new directory into the old directory (recursively).
Copy:
rsync -a SOURCE/ DEST/ --ignore-existing --whole-file
Move (no clobber):
rsync -a SOURCE/ DEST/ --remove-sent-files --ignore-existing --whole-file
Move (and clobber):
rsync -a SOURCE/ DEST/ --remove-sent-files --whole-file
Move, but only update with newer:
rsync -a SOURCE/ DEST/ --remove-sent-files --update --whole-file
