String comparison in single brackets in zsh

Question

Bash code to print all folders:

for f in ~/*;
do
if [ $f  == '/home/sk/.' -o $f  == '/home/sk/..' ]; then
       true
  else
     echo "$f"
  fi
done

It works on bash. When i ran the code on z shell, it threw error:

 = not found

Then I converted [ into [[, ] into ]] to avoid this error in z shell and ran it on z shell. It threw next error:

condition expected: $f

With [[ and ]], bash also throws error as:

syntax error in conditional expression
syntax error near `-o'

Is there a POSIX standard to do string comparison in shell, that works across shells?

Solution 1

There are various issues here. First, == is not standard, the POSIX way is =. Same goes for the -o. This one will work on both bash and zsh:

for f in ~/*;
do
if [ "$f"  = '/home/sk/.' ] || [ "$f"  = '/home/sk/..' ]; then
       true
  else
     echo "$f"
  fi
done

Note that your if is unneeded, dotfiles are ignored by default in both bash and zsh. You can simply write:

for f in ~/*; do echo "$f"; done

Or even

printf "%s\n" ~/*

Solution 2

Try:

if [ "$f" = '/home/sk/.' ] || [ "$f" = '/home/sk/..' ]

Comments

[terdon]

Are there any shells that will include dotfiles when expanding *? Neither bash nor zsh do.

[Janis]

@terdon; Not any shell that I know of. - Note that I was addressing just the OP's question in my answer, not any optimization beyond.

[terdon]

I understood that, hence my upvote. Since I'm pretty sure your knowledge of the shell ecosystem is far more extensive than my own, I thought I'd ask just in case :)

[Admin]

hi terdon, i have set shopt for dotglob set as off. But still i am getting . and .. inside the for loop in bash. so, i chose to do this fix... ls -a also lists the two entries - . and ..

[terdon]

@MadhavanKumar if you are seeing dotfiles, then dotglob is set somehow. They won't appear otherwise.

[Gilles 'SO- stop being evil']

@terdon Neither does by default, but ksh, bash and zsh can be configured to include dot files.

[Gilles 'SO- stop being evil']

@MadhavanKumar In bash, set GLOBIGNORE=.:.. to skip . and ..