This question is a sequel of sorts to my earlier question. The users on this site kindly helped me determine how to write a bash for
loop that iterates over string values. For example, suppose that a loop control variable fname
iterates over the strings "a.txt" "b.txt" "c.txt"
. I would like to echo
"yes!" when fname
has the value "a.txt"
or "c.txt"
, and echo
"no!" otherwise. I have tried the following bash shell script:
#!/bin/bash
for fname in "a.txt" "b.txt" "c.txt"
do
echo $fname
if [ "$fname" = "a.txt" ] | [ "$fname" = "c.txt" ]; then
echo "yes!"
else
echo "no!"
fi
done
I obtain the output:
a.txt
no!
b.txt
no!
c.txt
yes!
Why does the if
statement apparently yield true when fname
has the value "a.txt"
? Have I used |
incorrectly?
Best Answer
If you want to say
OR
use double pipe (||
).(The original OP code using
|
was simply piping the output of the left side to the right side, in the same way any ordinary pipe works.)After many years of comments and misunderstanding, allow me to clarify.
To do
OR
you use||
.Whether you use
[
or[[
ortest
or((
all depends on what you need on a case by case basis. It's wrong to say that one of those is preferred in all cases. Sometimes[
is right and[[
is wrong. But that's not what the question was. OP asked why|
didn't work. The answer is because it should be||
instead.