ulimit -Sv 1000    # 1000 KBs = 1 MB
ulimit -Sv unlimited # Remove limit

tar tf file.tgz
tar xf file.tgz filename

find . -size 20c       # By file size (20 bytes)
find . -name "*.gz" -delete # Delete files
find . -exec echo {} \;   # One file by line
./file1
./file2
./file3
find . -exec echo {} \+   # All in the same line
./file1 ./file2 ./file3

yes
yes hello

while inotifywait -e close_write document.tex
do
  make
done

cat file.txt | sort -R
cat file.txt | sort -R | head # Pick a random sambple
# Even better (suggested by xearl in Hacker news):
shuf file.txt

./script.sh
Type any input you want>
Ctrl-Z>     # send process to sleep
jobs -l      # find out the job id
disown -h jobid  # disown job
bg        # continue running in the background

timeout 10s ./script.sh
# Restart every 30 minutes
while true; do timeout 30m ./script.sh; done

sudo swapoff -a
sudo swapon -a

sudo fsck.ext4 -f -y /dev/sda1
sudo fsck.ext4 -v /dev/sda1
sudo mke2fs -n /dev/sda1
sudo e2fsck -n first block number of previous list> /dev/sda1

pdftk *.pdf cat output all.pdf    # Join PDFs together
pdftk A=in.pdf cat A5 output out.pdf # Extract page from PDF

cpdf -draft in.pdf -o out.pdf   # Remove images
cpdf -blacktext in.pdf -o out.pdf # Convert all text to black color

# Write random data, encode it in base64 and monitor how fast it
# is being sent to /dev/null
cat /dev/urandom | base64 | pv -lbri2 > /dev/null
# pv options:
#  -l, lines
#  -b, total counter
#  -r, show rate

apt-file update
apt-file search dir/file.h