Squoggle

Down & Dirty Notes on SED

Replace a word with another word:

To replace all instances of a certain word in a file with another word:

$ sed 's/[oldword]/[newword]/' file

This will not modify the original file but output to the screen

Strip the last letter of a list of words:

If you have a file with a bunch of words that all end in the same letter, something like this:

austin1a
denver1a
dallas1a
phoenix1a

and you want to strip the last letter off of each word you can do it with something like this:

$ sed 's/\(.*\)./\1/' file

Output is to screen.

Add a letter to the end of a list of words:

Lets say you want to add a letter to that list of words. You can do that like this:

$ sed 's/$/b/'file

This will add a letter b to the end of each word in the list.

Replace the last letter of word:

You can combine the above two commands and if you want to change all the of the a to letter b then you can do that like this:

$ sed 's/\(.*\)./\1/' file | sed 's/$/b/'

The first part of this command strips the last letter of each word. Then the second part of the command adds the letter b to the end of each word.

Add a trailing \

Many times you want to run a script against a list of servers or something. You can create a list with a space slash  \ after each word in the file:

$ sed 's/$/ \\/' file

The results will look something like this:

austin1a \
denver1a \
dallas1a \
phoenix1a \

Insert text at the beginning of a word:

If you want to insert the word router at the beginning of each word you could do something like this:

$ sed 's/^/router/' file

Insert text at the end of a word:

Same as above but at the end of the word:

$ sed 's/$/router/' file

Convert commas to newline:

Lets say you have CSV list in a file that looks something like this:

austin1a,denver1a,dallas1a,phoenix1a

and you want to convert those commas into newline. You can do something like this:

$ sed -e $'s/,/\\\n/g' file

Sometimes that list will have a space after the comma like this:

austin1a, denver1a, dallas1a, phoenix1a

You can modify the command slightly like this:

$ sed -e $'s/, /\\\n/g' file

Convert TABs (White space) to Commas:

Lets say you have a TAB separated file and you want to convert it to a CSV file. An example would be something like this:

austin1a.example.com. 300 IN A      10.10.20.10
denver1a.example.com. 300 IN A      10.10.30.10
dallas1a.example.com. 300 IN A      10.10.40.10
phoenix1a.example.com. 300 IN A     10.10.50.10

This command will convert any white space to a comma:

$ sed 's/[[:space:]]\+/,/g' file

Convert multiple spaces to single space:

Or if you simply want to convert multiple spaces to a single space you can do like this:

$ sed 's/[[:space:]]\+/ /g' file

More to come…