sed 's/cat/dog' pets

[vickey_20]

The sed command i.e stream editor , why does it need the starting 's' option
I have something like this

sed 's/cat/dog/' pets

It is supposed to replace all cat with dogs in the file pets. So does that 's' means to search , In the man pages -s specifies separate ???

[vickey_20]

I wonder what exactly these commands do .

sed -e 's/cat/dog/g'  -e 's/cat/dog/g' pets

and also what does this one do

sed -f myedits pets

thanks

[vonbiber]

The sed command i.e stream editor , why does it need the starting 's' option
I have something like this

sed 's/cat/dog/' pets

It is supposed to replace all cat with dogs in the file pets. So does that 's' means to search , In the man pages -s specifies separate ???

s as in 'substitute'
by the way if you want all the 'cat' replaced by 'dog' you must
type this

sed 's/cat/dog/g' pets

(g as in global)

[vickey_20]

thanks but what about the second one?

[lomcevak]

For the 2nd one, the manpage for sed states:

-f script-file, --file=script-file

add the contents of script-file to the commands to be executed

So in your example file myscripts would contain the command 's/cat/dog/g' in it (minus the single quotes). The advantage of using a file is that some sed commands can get quite long so it's easier to have them in a file and then specify that file when you run sed.

[vickey_20]

thanks lomcevak but what does the 'e' do? in the second part code 1

[lomcevak]

You really do have to start trying to understand manpages. For the -e option it states.

-e script, --expression=script

add the script to the commands to be executed

What this allows you to do is execute more that one sed command one a file. Your example isn't a good one because you're performing the same substitution twice.

sed -e 's/cat/dog/g'  -e 's/cat/dog/g' pets

This would make more sense.

sed -e 's/cat/dog/g'  -e 's/mice/rat/g' pets

In my example you're substituting cat with dog AND mice with rat.

You could also do this without the -e option by using the semi-colon( ; ) to separate sed commands like this:

sed 's/cat/dog/g; s/mice/rat/g' pets

[vickey_20]

thanks
see i if had just ended on man pages i wouldn't have learned the ';' thing.

[lomcevak]

Well yes and no. In the sed manpage it also says:

This is just a brief synopsis of sed commands to serve as a reminder
to those who already know sed; other documentation (such as the tex-
info document) must be consulted for fuller descriptions.

So in the case of sed the manpage is telling you to refer to other documentation for a better explanation of sed.

[vickey_20]

lol .......................