UNIX basic1

Regex basics

• *: zero or more
• +: one or more
• ?: zero or one
• .: any single character
• [^ ]: except
• ^: start
• $: end
• {n}: n repetitions
• {n,m}: n to m repetitions
• {,m}: m or fewer repetitions

grep

• grep -i: ignore upper/lower case
• grep -v: invert / not match
• grep -c: count of matching lines
• grep -w: whole word only

wc

• wc: word counter
• wc -c: characters
• wc -w: words
• wc -l: lines
• Default output includes lines, words, and characters

tr

• tr sourceChars destChars
• tr 'A-Z' 'a-z'
• tr -d '0-9': delete 0-9
• tr aeiou 12333: maps aeiou to 12333

head / tail

• head / tail: default 10 lines
• head -n {number} / tail -n {number}
• Combine them:

head -n 100 | tail -n 20

Character set example

• [a] = a

cut

• cut -f: tab-separated fields
• cut -c: characters
• cut -d: custom delimiter

Examples:

cut -f1,4
cut -d'|' -f1-3
cut -c1-5

sort

• sort -r: descending order
• sort -n: numeric sort
• sort -d: dictionary order
• sort -t: delimiter
• sort -k: column/key

Example:

sort -nr -k3

Meaning: sort by the 3rd column in descending numeric order.

uniq

• uniq -c: count duplicated lines
• uniq -d: print one copy of duplicated lines
• uniq -u: print lines that occur only once

Regex examples

[ab]+   -> a, b, aa, abb
(ab)+   -> ab, abab, ababab

To update later

• Add small input/output examples for each command
• Add notes on when to combine sort | uniq