Bashscripts.org

How to use an output of a command or a variable as regexp or replacement in sed ?

I'd like to use sed at this way :

ls -1 input.txt | sed 's/xxxx-xx-xx/`date +%Y-%m-%d`/g' > output.txt

or

d=`date +%Y-%m-%d`
ls -1 input.txt | sed 's/xxxx-xx-xx/`$d`/g' > output.txt

(where the output of the `date +%Y-%m-%d` command or content of $d variable can be used as replacement or regexp in sed)

But it seems like the sed doesn't recognise the commands..
Is there a way to be done ?

Thanks..

hi,


it's because of single quotes.
you may write :or

Oh,, they're working,,

but i dont understand why d=$(date +%Y-%m-%d)
i usually type d=`date +%Y-%m-%d` and it works..
and i dont understand too about the usages of such characters like ' " ` ( [ and {

where can i get those information ?

thanks..

Hi Mardon86!

Essentially, $(date +%Y-%m-%d) and `date +%Y-%m-%d` do exactly the same thing. Personally, I find it easier to read when using $(...). It's too easy to mistake the `back-tick` for a 'single-quote (apostrophe)', depending on the font that you're using.

It mostly makes it easier to read, and therefore easier for someone who didn't write the script to understand what's going on.

As for such characters like ' " ` ( [ and {, it really depends where they're being used. The Bash Scripting Guide and the Advanced Bash Scripting Guide at The Linux Documentation Project are great references for learning about those types of things.

I hope this helps!

oh,, thanks for helping,,

-SOLVED-

There is one more important difference. You cannot nest back quotes, but you can nest $()'s: