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Last modified: Mar, 2016

A collection of random but useful command lines. The OS is assumed to be Ubuntu.

Batch process images

To resize all images in one folder, first install imagemagick.

sudo apt-get install imagemagick

Then in the folder, run bash script:

for img in `ls *.JPG`
  mogrify -resize 50% $img


About IPv6 related commands: at the time of writing (Mar, 2016) IPv6 is still in the adopting stage and not every server can talk in IPv6.

  • To ssh into a IPv6 only Linux box:
ssh -6 user@3509:5600:02e4:0000:0000:0000:098e:2abf

which is very similar to the traditional way.

  • To ping IPv6 addresses/host names, do
ping6 ipv6.google.com

Directory and File Operations

  • Show meta information of hidden files with “du” (reference here):
du -sch .[!.]* * |sort -h
  • Change text pattern in files recursively:
find path_to_folder -type f -print0 | xargs -0 sed -i 's/patternA/patternB/g'

See this post for explanation.

  • Compare the content of files in two directories recursively:
diff -qr -x "*.o" -x "*.html" -x "*.bin" dir1 dir2

Here the “-x” flag excludes the files to be compared.

  • A “live” view of a log file using tail
cat log.txt | tail -f
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