c/linux · by Rick_C137@programming.dev · 322d

Check two conditions in bash ? [solved]

Hi,

I trying to test two condition together (AND) under bash but it's not working...

The goal is ti have True when two variables are either not set or empty (empty string)

I've tried

if [[ -n VARIABLE1 && -n VARIABLE2 ]]; then
    echo "OK"
fi

Here I get the "OK" no matter what .

Thanks.

22 points · 13 comments · view on lemmy.world

13 Comments

BillibusMaximus@sh.itjust.works · 8 pts · 321d (1 reply)

If you want true for empty strings, you want -z not -n

if [[ -z "VARIABLE1"  && -z "VARIABLE2"  ]]; then
    echo "OK"
fi

Farnsworth@lemmy.world · 3 pts · 320d

in [[ there is generally no need for quoting, except the right hand side of an = comparison

DeuxChevaux@lemmy.world · 7 pts · 321d (2 replies)

[ condition1 ] && [ condition2 ] && echo "Good" || echo "Bad"

suff@piefed.social · 14 pts · 321d

Explanation

[ is an alias for the program test, so you can call man test for more info.
&& is bash syntax for conjunction. In A && B, B will only be called if A returned a exit code >0 (error). You can call man bash for more info.
|| is bash syntax for disjunction. In A || B, B will only be called if A returned exit code =0 (success).
true and false are programs that just return exit codes 0 respectively 1.

Farnsworth@lemmy.world · 5 pts · 320d

Never use a && b || c. It is not the same as if a; then b; else c; fi: when a succeeds but b fails, it will run both b and c.

I would not bother with [ unless you absolutely need compatibility with non-bash shells.

harsh3466@lemmy.ml · 5 pts · 321d (1 reply)

To check for an empty string, use -z. -n checks to see if a string is not empty.

Farnsworth@lemmy.world · 2 pts · 320d

in [[, empty strings are falsy, so this also works:

[[ ! $VARIABLE1 && ! $VARIABLE2 ]] && echo "OK"

Rick_C137@programming.dev · 3 pts · 321d (2 replies)

Thank you all for yours input

What finally did work

if [[ -z VARIABLE1 && -z VARIABLE2 ]]; then
    echo "OK"
fi

If only Linux was using Python syntax that would be so much more intuitive...

sping@lemmy.sdf.org · 8 pts · 320d

Linux does use Python syntax... in Python.

In Bash though, it uses Bash syntax.

Farnsworth@lemmy.world · 2 pts · 320d

The variables need a dollar sign: $VARIABLE1

help test shows what -n and -z do.

dion_starfire@sh.itjust.works · 3 pts · 320d

You're probably wanting [ -z "${VAR1}" -a -z "${VAR2}" ]. Note in bash that there are minor differences in how [ ] and [[ ]] tests are handled. You can pull up a handy cheat sheet of the operands on most distros by running man test, though you'll need to read through the CONDITIONAL EXPRESSIONS section of man bash if you want to see the minor differences of the single vs double square bracket commands (mostly whether locale applies to string order, as well as whether operands are evaluated in numeric comparisons).

thingsiplay@beehaw.org · 2 pts · 321d

Try this:

#!/usr/bin/env bash

a=""
if [[ -z "${a}" && -z "${b}" ]]; then
    echo "OK"
else
    echo "Not OK"
fi

a="OK"
if [[ -n "${a}" && -z "${b}" ]]; then
    echo "More ${a}"
else
    echo "More Unokay"
fi

fubarx@lemmy.world · 1 pts · 321d

Could try:

if [ condition1 ] && [ condition2 ]; then
  echo "OK"
fi