cut

# cut - select columns of text from each line of a file
# if you're needing more comprehensive pattern-directed 
# scanning and processing, take a look at `awk`

# Given a text file (file.txt) with the following text:
# unix or linux os
# is unix good os
# is linux good os

# cut will return the fourth element if given:
cut -c4 file.txt
x
u
l

# cut will return the fourth and sixth element if given:
cut -c4,6 file.txt
xo
ui
ln

# cut will return the fourth through seventh element if given:
cut -c4-7 file.txt
x or
unix
linu

# to use cut like `awk` you could do the following to return the 
# second element, delimetered by a space:
cut -d' ' -f2 file.txt
or
unix
linux

# in the same way as above you can modify -f to return varying results:
cut -d' ' -f2,3 file.txt
or linux
unix good
linux good