I am trying to get all possible combinations of a of strings within a certain command, except when the strings are the same. I simplified what I'm trying to do and how I tried to do it as follows:
for i in a b c
do
for p in a b c
do
if [ $i -ne $p ]
then
echo "$i and $p"
fi
done
done
The output I expect is:
a b
a c
b a
b c
c a
c b
But it does not seem to work.. any ideas what's wrong with my nested for loops?
Replace :
if [ $i -ne $p ]
With :
if [ "$i" != "$p" ]
The -ne operator requires integers. The != operator works on strings.
You should usually double quote strings in tests, unless you are really, really sure they cannot contain more than one word (as seen by the shell following word splitting).
If using Bash, you can use the Bash-specific [[ ]] test construct.
if [[ $i != "$p" ]]
Double quotes are generally not needed in this type of test, as instead of being a command, it is special shell syntax and is not exposed to word splitting. However, the right-hand part of the comparison should be quoted to disable pattern matching, unless you are absolutely sure no string that will ever be used there could trigger pattern matching.
help test