use multiple conditions in 'test' command - bash

Question

I have been trying to convert the following code to use 'test' instead of 'if'
if [ -e ./blah ] && [ ! -L ./blah ];
then
exit 1
fi
My intention is to use test instead, so that I dont have to exit 1 explicitly. I am trying something like this:
test -e ./blah && ! -L ./blah;
instead of &&, I have tried -a, with different bracket combinations, but I am not successful. I am sure there should be a simple way to do this. Can anyone help me ?

Answer 1

test does not understand logical operators && and ||. You can use test -e ./blah -a ! -L ./blah, but if you are using bash, you can also switch to its more powerful [[ .. ]] construct:
[[ -e ./blah && ! -L ./blah ]]

Answer 2

To make if [ -e ./blah ] && [ ! -L ./blah ]; work, use the following
if [ -e ./blah -a ! -L ./blah ]; (-a stands for and) http://tldp.org/LDP/abs/html/comparison-ops.html
Demo -- http://ideone.com/GR8UiK
But, as others have pointed out, [[ .. ]] construct is more powerful than [...].

Answer 3

You can combine them all (including if then fi):
[[ -e ./blah && ! -L ./blah ]] && exit 1

Answer 4

Use [[ keyword as it is more powerful.
if [[ -e ./blah && ! -L ./blah ]]
then
...
fi
However, to ensure portability, you can do something like this too
if [ -e ./blah ] && [ ! -L ./blah ]
then
...do something
fi

Answer 5

As you ask to use test, you can do like so:
test -e ./blah && test -L ./blah || ( echo 'First action' ; echo 'Second action )
The different operators (&&, ||, etc...) are first parsed by the shell, so you can't use it in command parameter(s).

Answer 6

if [ -e ./blah ] && [ ! -L ./blah ];
is equivalent to
if test -e ./blah && test ! -L ./blah;
Therefore you can simply write
test -e ./blah && test ! -L ./blah
To wit:
$ help [\[] | tail -n +3
[: [ arg... ]
Evaluate conditional expression.
This is a synonym for the "test" builtin, but the last argument must
be a literal `]', to match the opening `['.

Answer 7

Do the following:
$ ls -i /bin/test
54008404 /bin/test
$ ls -i /bin/[
54008404 /bin/test
That 54008404 is the inode number. This is the real name of a file. The /bin/test simply points to the inode and the inode contains all file file information.
The thing to note is that /bin/[ and /bin/test are the same inode. That means, they're the same command.
Thus:
if [ -f "$foo" ]
is the same as:
if test -f "$foo"
The if command executes the command given, and then will execute the if clause if the command returns true and doesn't execute the clause if the command it false.
For example:
if grep -q "foo" $foo
then
echo "File $foo contains the regular expression /foo/"
fi
Is completely valid. The grep -q command (in many variants of grep means search for the regular expression, and if that regular expression is in the file, return an exit code of 0 (which means the command succeeded and is true).
Note there is no square brackets.
The test command (or [...]) merely runs a test as specified, and returns with an exit code of 0 (thus the command is a success) if the test is true. That's all it does.
You may also see this construct:
[ "$foo" = "$bar" ] && echo "$foo is equal to $bar"
The && means execute the next command (and return the exit code) if the first command returns an exit code of zero. Otherwise, simply return the first command's exit code.
Thus:
if [ -e ./blah ] && [ ! -L ./blah ];
is saying run test -e ./blah and if that is true (that is, the file exists) execute test ! -L ./blah and if that is also true, run the if clause of the statement.
Note that [ -e ./blah] and [ ! -L ./blah ] are two separate commands. The && strings together the two commands:
[ "$foo" = "$bar" ] && some_command;
This says, run test "$foo" = "$bar" and if that is true, run the command some_command. Note that this is equivalent to:
if [ "$foo" = "$bar" ]
then
some_command
fi
The other list structure is the ||. This means that if the first command succeeds, return an exit code of 0 and don't run the second command. Thus:
[ "$foo" = "$bar" ] || some_command;
Is the same as:
if [ "$foo" = "$bar" ]
then
:
else
some_command
fi
Let's get back to your _original question:
if [ -e ./blah ] && [ ! -L ./blah ];
then
exit 1
fi
Is the same as:
if test -e ./blah && test ! -L ./blah
then
exit 1
fi
Which is the same as
test -e ./blah && test ! -L ./blah && exit 1
This means: If test -e ./blah is true (./blah is a file), then execute the command after the && list operator. This is test -! -L ./blah. If this test also is true, run the command after the && list operator again.
This could also be rewritten as:
test -e ./blah && test -L ./blah || exit 1
This says that if test -e ./blah is true, run the command after the && list operator. If test -L ./blah is false, run the command after the || operator.