Input/Output Processing#

Command Action
cat Output files to stdout
sort Sort the lines in a file
uniq Remove repeated lines
grep Search for patterns in a file
wc Count the lines, words and characters in a file
head Output the first lines of a file
tail Output the last lines of a file
tee Split a stream like a pipe tee

Building a Pipleline#

In this example I use the spell program to find misspelled words in the spellk file. The uniq program removes duplicate lines but there’s a catch, the repeated lines have to be next to each other. That’s why uniq is always paired with sort to guarantee that duplicates are on adjacent lines. Finally I use a tee to see the output and also capture it to a file.

Counting Words#

The wc program gets it’s name from “word count” but it’s more frequently used to count lines.

The wc command can be useful in a pipeline. Here’s how to count all of the files in your home directory. Note how stderr from find is redirected to /dev/null to suppress error output.

Grepping for Love#

The grep program looks for words inside of text files. It prints the lines where words are located. This demonstration shows the common uses of grep.