Shell script with sudo sh

Question

I want to make a script to install a program (ROS) and I need to write this line:

 sudo sh -c 'echo "TEXT VARIABLE TEXT" > systemFile'  # to write in systemaFile I need sudo sh

if echo is just fixed text, it works. If echo is text + variable it doesn't work.

I've tried with:

read f1 < <(lsb_release -a | grep Code* | cut  -f2)   #codename is writted in variable $f1
echo $f1 # retruns "quantal" as I expected
sudo sh -c 'echo "TEXT $f1 TEXT" > systemFile'  #f1 is empty, WHY?

Then I have to assign the variable inside the same instruction sudo sh, for example:

sudo sh -c ' read f1 < <(lsb_release -a | grep Code* | cut -f2) ; echo "TEXT $f1 TEXT" > systemFile'

sh: 1: Syntax error: redirection unexpected

& regd why your command does not work: variable expansions don't happen inside single quotes. — anishsane, Jul 07 '14 at 08:51

score 2 · Accepted Answer · answered Jul 07 '14 at 08:35

2

Please try just like this script line

sudo sh -c 'echo TEXT '$f1' TEXT > systemFile'
sudo bash -c 'echo TEXT '$f1' TEXT > systemFile'

i have use this able script line in .sh file and its working fine.

answered Jul 07 '14 at 08:35

Kalpesh Gamit

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score 2 · Answer 2 · answered Jul 07 '14 at 08:48

2

This can work too:

sudo sh -c "echo 'TEXT $VARIABLE TEXT' > systemFile"

However, it is generally not recommended to un-necessarily run a command as sudo. You seem to want only redirection to be "sudoed". So try these options:

echo "TEXT $VARIABLE TEXT" | sudo tee systemFile >/dev/null
echo "TEXT $VARIABLE TEXT" | sudo dd of=systemFile

echo can be simple echo, or any other command you want. Note that this command is not being run under sudo.

answered Jul 07 '14 at 08:48

anishsane

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# to write in systemaFile I need sudo sh - already mention in question – Programmer Jul 07 '14 at 10:15
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^^ NO. try the `sudo dd`/`sudo tee` options. You don't need to use `sudo` for `sh`. – anishsane Jul 07 '14 at 15:34
Check this question for other options : http://stackoverflow.com/q/17396951#answers – anishsane Jul 07 '14 at 17:13

score 1 · Answer 3 · edited Jun 20 '20 at 09:12

1

use -E option to run sudo:

sudo -E sh -c 'echo "TEXT VARIABLE TEXT" > systemFile'

from man sudo:

-E

The -E (preserve environment) option indicates to the security policy that the user wishes to preserve their existing environment variables. The security policy may return an error if the -E option is specified and the user does not have permission to preserve the environment.

edited Jun 20 '20 at 09:12

Community

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answered Jul 07 '14 at 08:54

Farvardin

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etheranger · Answer 4 · 2014-07-07T08:59:52.847

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Shell variables are only expanded in "double quotes", not in 'single quotes'.

$ v=value

$ echo $v
value

$ echo "$v"
value

$ echo '$v'
$v

You're starting a new instance of sh which then runs the command echo "TEXT $f1 TEXT" > systemFile.

Since $f1 has not been assigned within the new process, it's empty.

To fix this, you can expand $f1 and pass it in the command line:
sudo sh -c 'echo "TEXT '$f1' TEXT" > systemFile'

Or export it so it's available to the child process (using -E to preserve the environment, thanks anishsane):
export f1
sudo -E sh -c 'echo "TEXT $f1 TEXT" > systemFile'

edited Jul 07 '14 at 08:59

answered Jul 07 '14 at 08:51

etheranger

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`sudo` does not pass `export`s to its children it seems. Same command without sudo prints properly when exported. – anishsane Jul 07 '14 at 08:53
On another note, `'echo "TEXT '$f1' TEXT"` should be `'echo "TEXT '"$f1"' TEXT"`, in case `$f1` contains spaces or special characters. – anishsane Jul 07 '14 at 08:55
@anishsane ah, I forgot you need the `-E` flag to preserve env vars. But no, it works fine without the extra double quotes for me. – etheranger Jul 07 '14 at 08:57
as per your instruction i have try and results like #f1 is empty, WHY? – Programmer Jul 07 '14 at 10:17

Shell script with sudo sh

4 Answers4