bash to edit one line of a file

Frayed · 04-21-2008, 12:27 PM

Hi - how would I use bash scripting to edit one line of a file? I have a file thats is several hundred lines long. Each line ends in a '%' character. I want to remove the '%' character from the last line only. Thanks.

ararus · 04-21-2008, 12:36 PM

edit:
Ignore this, nothing to see here, move along. Spurious PEBKAC interrupt detected.(Note to self: Engage brain for more than 0.3 seconds before posting).

Proceed directly to osor's post below.

endedit.

how about:

Code:

echo -e "\n" | dd bs=1 count=1 of=$file seek=$(( $(stat -c %s $file) - 2))

I'm assuming you want to retain the newline, this replaces the last two bytes (i.e. "%\n") with "\n".

osor · 04-21-2008, 01:03 PM

Code:

sed -ie '$s/%$//' filename

pixellany · 04-21-2008, 02:06 PM

I strongly recommend the sed solution (or one using awk or another tool)

"dd" is the ultimate power tool and will do major damage with just a small typo. I would NOT use it where other tools are available

davimint · 04-21-2008, 09:22 PM

Just learning sed but shouldn't it be.

Code:

sed -ie 's/%$//' filename

instead of

Code:

sed -ie '$s/%$//' filename

I've never see the "$" which normally "Matches the end of a line" in front
of the s-command for substitution.

osor · 04-21-2008, 09:26 PM

Quote:

Originally Posted by davimint

I've never see the "$" which normally "Matches the end of a line" in front
of the s-command for substitution.

This is the address for the substitution. In an address context, ‘$’ means perform the command on the final line of input.

davimint · 04-21-2008, 09:31 PM

Osor

Once again I read a post wrong, but thanks for the explanation. Gosh, I need to buy a book on "Sed" I don't think I'll every understand it Someone always shows me something I have not seen before.

Someday I'll get it.

gilead · 04-21-2008, 10:24 PM

Quote:

Originally Posted by davimint

Gosh, I need to buy a book on "Sed" I don't think I'll every understand it Someone always shows me something I have not seen before.

I have O'Reilly's sed & awk, but there's plenty of info online, for example - here

pixellany · 04-22-2008, 07:13 AM

The Grymoire link is my favorite tutorial--look up addresses and address ranges.