Whilst most of the following commands perform quite simple operations they can be combined together, using shell scripts and UNIX pipes (chaining the output from one command directly into the input of another), to perform extremely complex operations. Most of the following commands have mulitple flag options, and so it is best to read the manual pages.

perl

Perl is an interpreted language optimized for scanning arbitrary text files, extracting information from those text files, and printing reports based on that information. It's also a good language for many system management tasks.

awk

A pattern scanning and processing language.

sed

sed is a stream editor which copies the input filenames specified (standard input default) to the standard output, edited according to a script of commands.

cut

Remove selected fields from each line of a file.

cat

Cat reads input from files, or from standard input, and displays it on the standard output.

sort

A utility to sort and collate files.

uniq

Remove or report adjacent duplicate lines.

wc

Display a count of lines, words and characters.

tr

Apply a translation to characters, eg NEWLINE to SPACE.

grep, fgrep and egrep

Search a file for a string or regular expression.

echo

Echo arguments to the standard output.

tail

Display the last part of a file.

more

Browse or page through a text file, one screen at a time.

less

An Interactive file browser.

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