Text Filters

Command	Purpose
`cat` / `tac`	Print / print reversed
`head -n` / `tail -n`	First / last N lines
`tail -f`	Follow a growing file
`sort` / `sort -n` / `sort -r`	Sort (numeric / reverse)
`uniq -c`	Collapse & count duplicate adjacent lines
`cut -d: -f1`	Extract fields
`tr 'a-z' 'A-Z'`	Translate characters
`wc -l`	Count lines
`nl`	Number lines

$ cut -d: -f1 /etc/passwd | sort | head -3
avahi
backup
bin

Exam trap: uniq only removes adjacent duplicates - always sort first: sort file | uniq -c.