[SOLVED] a problem with sed when a variable has '/' character.

corone · 04-09-2012, 02:19 AM

Hi,
I want to parse and modify a file.

input file:

Code:

$ cat input_file
date : 01/01/2011

output file which I expect:

Code:

$ cat output_file
date : 04/09/2012

A variable NEW_DATE already has a value 04/09/2012.

Code:

NEW_DATE=04/09/2012

I tried the following command.

Code:

$ sed "s/Date :.\+/Date : $NEW_DATE/" input_file > output_file

But,
because the variable NEW_DATE includes '/' characters,
a problem occurs with the above command.

Can this problem be solved?
I cannot modify the value of the variable NEW_DATE.

Thank you.

syg00 · 04-09-2012, 02:36 AM

Use a different character for the separator - say "@".

fukawi1 · 04-09-2012, 02:37 AM

You can possibly get away with using pipe "|" or colon ":" for substitution delimiters with sed.
ie:

Code:

sed "s|foo|bar|g" somefile

corone · 04-09-2012, 03:38 AM

Thank you for your answers, syg00 and fukawi1.

David the H. · 04-09-2012, 07:12 AM

It seems to me that you may be making it more complicated than necessary. If there's only that single entry, what's keeping you from simply creating the entire output file directly?

Code:

echo "date : $NEW_DATE" >output_file

By the way, environment variables are generally all upper-case. So while not absolutely necessary, it's good practice to keep your own user variables in lower-case or mixed-case, to help differentiate them.

corone · 04-09-2012, 11:48 PM

Thank you for your reply, David the H.
The given example is much omitted.
Actually, the format file has many entries.

But it is too much omitted.
It's my mistake.
I didn't think that far for the others. Sorry.

Quote:

Originally Posted by David the H.

By the way, environment variables are generally all upper-case. So while not absolutely necessary, it's good practice to keep your own user variables in lower-case or mixed-case, to help differentiate them.

Thank you for your tip.
I won't forget the tip.

David the H. · 04-10-2012, 09:48 AM

No problem then. But it does pay sometimes to step back and look at your requirements a different way. Often you find that things don't need to be as complex as you originally believe.

Indeed, you can still use my idea. Just use sed's "c" (change) command instead of "s" (substitute).

Code:

sed -i "/^date/c date : $new_date" file.txt

I've also worked out the commands needed to do it in ed, which is an actual text editor. It's almost identical.

Code:

printf '%s\n' '/^date/c' "date : $new_date" '.' ',p' | ed -s file.txt

printf '%s\n' '/^date/c' "date : $new_date" '.' 'w' | ed -s file.txt

The ",p" command at the end simply prints the changed contents to stdout. Changing it to "w" writes them back to the file.

How to use ed:
http://wiki.bash-hackers.org/howto/edit-ed
http://snap.nlc.dcccd.edu/learn/nlc/ed.html
(also read the info page)

Here are a few useful sed references.
http://www.grymoire.com/Unix/Sed.html
http://sed.sourceforge.net/grabbag/
http://sed.sourceforge.net/sedfaq.html
http://sed.sourceforge.net/sed1line.txt