Bash string substitution for sed argument: Sed: unknown command: `''

Question

I'm trying to make a function in .bashrc to run this command:

lspci -kvnn | sed -n '/VGA/,/^$/ p'

, where VGA would be substituted with the first argument $1.

This is what I came up with:

lsp(){
    sed_str="'/$1/,/^$/ p'"
    echo $sed_str
    lspci -kvnn | sed -n $sed_str
    return
}
export -f lsp

I cannot understand why the function fails, the echo $sed_str (there for troubleshooting) output looks exactly the same as the regex in the first command. Still sed is complaining:

[user@linux ~]$ lsp VGA
'/VGA/,/^$/ p'
sed: -e expression #1, char 1: unknown command: `''
[user@linux ~]$

There's probably something obvious I'm not seeing here.

Kernel and shell:

uname -r      -> 5.8.14-arch1-1
echo $SHELL   -> /bin/bash

Welcome to SE, Raflemakt ! When an answer is provided to you and you are satisfied with it, you can formally accept it, and also upvote it. To accept it please select the greyed check mark located left below the upvote score. This way others will instantly recognize that your question has a valid answer. Incidentally the answerer will also get rewarded with karma points. ;-) — Cbhihe
– Cbhihe, Commented Oct 12, 2020 at 20:41
Thank you! I didn't know about accepting an answer (which is hard when you have two helpful answers). I did upvote them, though. However it seems upvotes from new accounts with less than 15 reputation aren't showed publicly. :) — Raflemakt
– Raflemakt, Commented Oct 12, 2020 at 21:44

B. Morris · Accepted Answer · 2020-10-12 15:32:25Z

1

You have quotes within your string, not just delimiting your string. You need to use quotes to define your string as well as use it:

lsp(){
    sed_str="/$1/,/^$/ p"
    echo $sed_str
    lspci -kvnn | sed -n "$sed_str"
    return
}
export -f lsp

answered Oct 12, 2020 at 15:32

B. Morris

1525 bronze badges

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Rakesh Sharma · Accepted Answer · 2020-10-12 15:34:39Z

1

>>> sed_str="/$1/,/^\$/p"

>>>> lspci -kvnn | sed -n "$sed_str"

The single quotes are the source of trouble. Also you need to double quote the $sed_str variable to protect it from word splitting nd file name expansion after it has been expanded.

Since you did not quote your variables so it appears as following to the shell

 ... ¦ sed -n '/VGA/,/^$/ 'p

arg1 =   -n
arg2 =  '/VGA/,/^$/
arg3  = 'p

see 2 and 3 don't make sense to sed and it is complaining for that. It thinks ' is some sed command.

answered Oct 12, 2020 at 15:34

Rakesh Sharma

1,1021 gold badge6 silver badges3 bronze badges

Thank you for the clarification, removing the extra single quotes and putting quotes around $sed_str solved the issue, as B.Morris also pointed out.

Raflemakt
– Raflemakt

2020-10-12 15:39:51 +00:00
Commented Oct 12, 2020 at 15:39

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