CODEWITHSUNDEEP
bash
PsyKoptiK
PsyKoptiK

Reputation: 35

How to suppress the single quote character in an echo command?

If I execute this command directly from CLI, I don't have any problem:

~ # apt autoremove 1>$- 2>$-
~ #

But if I call it from a script I have some errors: Here is the script:

#!/bin/bash -x
NOVERBOSE='1>$- 2>$-'
apt autoremove $(echo ${NOVERBOSE})

And here is the output:

~ # /bin/bash -x test2.sh
+ NOVERBOSE='1>$- 2>$-'
++ echo '1>$-' '2>$-'
+ apt autoremove '1>$-' '2>$-'
Reading package lists ... Done
Building the dependency tree
Reading status information ... Done
E: Unable to find package 1> $
E: Unable to find a package matching the regular expression "1> $"
E: Unable to find package 2> $
E: Unable to find a package matching the regular expression "2> $"

I don't understand why echo add some singles quotes around each part of the variable.

Upvotes: 1

Views: 92

Answers (2)

chepner
chepner

Reputation: 530920

NOVERBOSE should be a flag that indicates the desire to suppress output, not the syntax to do so. You then test the value and redirect output (or not) as appropriate.

if [[ $NOVERBOSE = [Yy]* ]]; then  # e.g., y, Y, yes, Yes, etc
    apt autoremove > /dev/null 2> /dev/null
else
    apt autoremove
fi

If you don't like running apt "twice" like this, you can redirect to /dev/stdout and /dev/stderr explicitly as a no-op redirection.

if [[ $NOVERBOSE = [Yy]* ]]; then
  out=/dev/null
  err=/dev/null
else
  out=/dev/stdout
  err=/dev/stderr
fi

apt autoremove > "$out" 2> "$err"

Upvotes: 4

Barmar
Barmar

Reputation: 780724

echo isn't adding quotes, that's just how the -x option shows where each argument begins and ends.

The problem is that I/O redirections are not processed after expanding variables. You need to use eval to re-parse the line.

eval "apt autoremove $NOVERBOSE"

Upvotes: 2

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