my short but growing list of bash one-liners i find useful

bash-one-liners.txt

# Print specific line in file with sed
sed -n '07p' filename

# print line in file matching weeknumber
sed -n ''$(date +%V)'p' filename

# remove blank lines
sed '/^\s*$/d'

# print longest line in file
cat filename|awk '{print length, $0}'|sort -nr|head -1

# Scan network for active hosts
nmap -sP 10.0.0.0/24

# Same as above, but keep only addresses and sort them
nmap -sP 192.168.3.0/24 | grep report | cut -d' ' -f5,6 | sort

# Scan for open ports (require root)
sudo nmap -sS -O 10.0.0.249

# Replace spaces in file names
find -name "* *" -type f | rename 's/ /_/g'

# Flip a video 90 degrees clockwise
avconv -i in.mp4 -vf "transpose=1" -strict -2 out.mp4

# calculate n weeks from now
date -d 'now + n weeks'

# Calculate n weeks from any date
date -d 'Aug 4 + n weeks'

# Extract a specific string from all links in a webpage using curl, grep and sed
curl "http://www.gutenberg.org/wiki/Adventure_(Bookshelf)" | grep "www.gutenberg.org/ebooks/" | sed 's/.*ebooks\///' | sed 's/" class=.*//' > gutenberg-adventure-bookids.txt

# convert a video to gif using ffmpeg and gifsicle
ffmpeg -i in.mov -s 600x400 -pix_fmt rgb24 -r 10 -f gif - | gifsicle --optimize=3 --delay=3 > out.gif

# Run one command through ssh connection and exit by simply adding a trailing command
ssh user@host command

# Resize all .png-images
for f in *.png; do convert $f -resize 1000x900 1000px_$f; done

# Create a video from a set of images
ffmpeg -pattern_type glob -i '*.jpg' -pix_fmt yuv420p out.mp4

# Make a collage of images with five columns and fill automatically numbers of rows
montage -geometry +0+0 -tile 5x *.jpg result.jpg