Sed

Still under construction

GREP substitute

sed -n /PATERN/p

Writing output to the input file

To write directly to the same file used as input, use the command option “-i

mycomputer ~ $ echo '123' > testfile.txt

mycomputer ~ $ cat testfile.txt
123

mycomputer ~ $ sed -i s/123/abc/g testfile.txt

mycomputer ~ $ cat testfile.txt
abc

Print line 25 of a file

sed 25!d <file>    or    sed -n 25p <file>

(or awk NR==25 faces.txt    or    head -25 faces.txt | tail -1  )

To display system users & their default login shell, you will write:

sed -e 's/:.*:/:/' /etc/passwd

To list last logged in users except for root, you will write:

last | sed '/^root /d'

Sed tutorials

http://www.grymoire.com/Unix/sed.html