Strings mangling-greping

replace:
sed -e 's/oldtext/newtext/g'

Removing the last three characters from every filename
cat files | sed 's/\(.*\).../\1/'

Removing first character from each filename/string
cat files |sed 's/.\(.*\)/\1/'

Removing last character from each filename/string
cat files |sed 's/\(.*\)./\1/'

Delete line feed: 
sed ':a;N;$!ba;s/\n/ /g'

dos2unix:
tr -d \\r < win.txt > unix.txt

unix2dos:
sed -e 's/$/\r/' < unix.txt > win.txt

Print first field:
awk '{print $1}' file

Print first field using a delimiter:
awk -F ";" '{print $1}' file

Print last field using a delimiter:
awk -F "/" '{print $NF}' file

Print 3 first fields of an ip address:
cut -d '.' -f 1-3

Print only strings with >=8 char:
awk 'length>=8'

Print IP addresses:
grep '[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}'
egrep "[0-9]+\.[0-9]+\.[0-9]+\.[0-9]"

Print the beginning of a string:
grep '^xxx' file

Print the end of a string:
grep 'xxx$' file

Print 3 lines before the match:
grep -B 3 string file

Print 3 lines after the match:
grep -A 3 string file

Don't print the 2st char:
cut -c3-10

Don't print empty lines:
grep -v "^$"

Sum of numbers on multiple lines:
tr -d \\r | paste -sd+ | bc

Sort by string size:
sort -n

Merge columns of 2 files:
paste -d' ' file1 file2
pr -mts' ' file1 file2
sed -e 's/ //g'