Wiki: Bash

Basic tips

Use for …;{ …;} instead of for …;do …;done
Use $[…] instead of $((…)) for arithmetic expansion
Try to use && or || instead of if
: is a short command that does nothing
history -p prints each argument on a new line
Unset variables evaluate to 0 in arithmetic expressions

Parameter expansion

Parameter expansion is useful to get or replace substrings, get the length of values or change the case of strings.

a="Hello, World!"
echo ${a:0:5}  # Hello
echo ${#a}     # 13
echo ${a//o/O} # HellO, WOrld!
echo ${a@U}    # HELLO, WORLD!
echo ${a@L}    # hello, world!