Threaded Mode | Linear Mode

codecaine · 12-28-2009, 08:07 PM

First let me show you explain some special characters in sed that I will use in this example.

$ - is that special character meaning the end of a line
^ - is a special character meaning the beginning of a line
. - means any character of the character before it or nothing. Example [a-z]. means any character from a-z
? - mean any character

Since everybody has a /etc/passwd on unix systems. I will use that file for displaying data.

First lets go over the print command in sed. sed will print command prints any pattern that match. You need to use the -n parameter when printing or it will just print duplicates for lines found.

Say you only wan to print certain lines in a file. The code below will print the first 2 lines in the passwd file

Code:

sed -n 1,2p /etc/passwd

If you want to print line from 2 to 5 you would do this

Code:

sed -n 2,5p /etc/passwd

If you want to print lines 4 to the end you would do this. Notice when using special characters you need to use single quotes because bash may also use this single character. It is a good habit to just put everything in single quotes.

Code:

sed -n '4,$' /etc/passwd

Now that we got out how to printing a range of lines. Let print matching cases. say you want to see all the user using the bash you would do as follows. You would put you patter in between / / followed by a p. This code below only prints lines that has the word bash in it

Code:

sed -n '/bash/p'

If you want to print all lines that begin with a s you would do as follows. Remember that the ^ is a special character meaning beginning. If you did not put this in there it will just look through the online line and any line that had a s would be printed

Code:

sed -n '/^s/p' /etc/passwd

If you want to print a line that has any character that start with a range of characters you can do this. This command will start for any lines that begin with a or a r

Code:

sed -n '/^[ar]/p' /etc/passwd

If you wanted to print a line that has a word that had r and t in it with any 2 character in between you would do to this. Remember the ? mean any character. If you have root installed you probably will find that line Smile

Code:

sed -n '/r??t/p' /etc/passwd

my last printing example is print between b and h with any range of characters in between. This will print any lines that a r and t after the r

Code:

sed -n '/r.*t/p' /etc/passwd

There is so much more you can do with sed with printing but this is the basics