help with some commands

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# 1  
help with some commands

i'd like from someone to explain me 'what is what' from these parts of code if it's possible.i'd like to understand them and their usage:
sed '3d' filename

sort –t: +0 -1 /etc/passwd

and also this:
tr ‘[0-9]’ ‘[+*10] ‘ < filename

thank you!

Last edited by strawhatluffy; 01-23-2012 at 03:27 PM.. Reason: Code tags!
# 2  
man pages

Have you looked at the man pages for each command?
For instance, type
man tr

will tell you about the tr command
# 3  
ok i got this about the tr command...
but what about the first command with sed and the second with sort?can you explain me these please?
# 4  
I think the sed expression there deletes the third line.

sed is a complicated language based on regular expressions and a complete explanation of its abilities would fill books. A small outline may be accessed with 'man sed'.
# 5  
maybe the command
sed '3d' filename

if i write it somewhere in my script replaces the sting '3d' withe the contents of the filename?
# 6  
no, it prints the contents of 'filename' to your terminal with the third line deleted, as described above.
# 7  
ok..i got it...'3d' in sed means delete the third line....and i thank you for this..
if i had sed in this form what this could mean:
sed '2s/home/george/' filename

whats the meaning of the '2s'??

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