sed: a quick reference

$ echo "abc"
abc

$ echo "abc" | sed 's/b/z/'
azc

$ echo "abcb" | sed 's/b/z/'
azcb

$ echo "abcb" | sed 's/b/z/g'
azcz

$ echo "abc123def" | sed 's/[0-9]/(&)/'
abc(1)23def

$ echo "abc123def" | sed 's/[0-9]*/(&)/'
()abc123def

$ echo "abc123def" | sed -r 's/[0-9]+/(&)/' 
abc(123)def
# The original sed did not support the "+" metacharacter. GNU sed does if you use the "-r" command line option, which enables extended regular expressions.

$ echo "abc123def" | sed 's/[0-9]/(&)/2'
abc1(2)3def

$ echo "abc" | sed 's/[a-z]/\U&/'
Abc

$ echo "abc" | sed 's/[a-z]/\U&/g'
ABC

$ echo "abc" | sed 's/[a-z]/\U&/2g'
aBC

$ echo "ABCabc" | sed 's/a/(&)/Ig'
(A)BC(a)bc

$ echo "hello world" | sed 's/\<./\U&/g'
Hello World
# please check 'Additional GNU Extension' in http://www.regular-expressions.info/gnu.html

$ echo -e "abc\npqr" 
abc
pqr

$ echo -e "abc\npqr" | sed 's/b/z/'
azc
pqr

$ echo -e "abc\npqr" | sed 's/b/z/p'
azc
azc
pqr

$ echo -e "abc\npqr" | sed -n 's/b/z/'

$ echo -e "abc\npqr" | sed -n 's/b/z/p'
azc

# remove commented line from a configuration file
$ sed -e 's/#.*//' -e '/^$/ d' squid.conf > tem_squid.conf