Print only line 58 of a text file:

$ sed -n '58p' file.txt



The '-n' option suppresses printing of all lines

Batch renaming of files

$ rename 's/\s+/_/g' *.mp3

Renames all mp3 files, stripping off all spaces and substituting it with underscore.

The set command

#!/bin/sh
set `date`
echo "Time: $4 $5"
echo "Day: $1"
echo "Date: $3 $2 $6"

Returns:
Time: 01:33:02 EEST
Day: Sat
Date: 24 Jul 2005

The set command captures the positional parameters of `date` which has the format:

Sat Jul 24 01:33:02 EEST 2005

Positional parameters

myscript.sh:

#!/bin/sh
echo $0 $1 $2 $3

$ ./myscript.sh Running Ubuntu Hoary
./myscript.sh Running Ubuntu Hoary

$* contains all the positional args

$# contains the number of arguments passed

Ignore case in grep

$ grep -i 'camelCaseWhatever' file.txt