I am running this on Linux:
$ number=4 $ test $number -eq 4 $ echo $? 0 $ test $number -lt 2 $ echo $? 1
Are the results (0 and 1) true ?
Unix & Linux Stack Exchange is a question and answer site for users of Linux, FreeBSD and other Un*x-like operating systems. It only takes a minute to sign up.Sign up to join this community
On Unix systems, utilities return a zero exit-status if what they did went well, if it succeeded without errors etc. If a utility fails, it returns a non-zero exit status.
This way, it's possible to tell a user with the exit-status what when wrong (see e.g. the "EXIT VALUES" or similar section of some manuals, for example the manual of
rsync). In short, if the operation succeeded, the exit-status is zero and if it's not zero, it failed and the exit-status may say why it failed.
test utility, which you use, follow this pattern in that if a comparison succeeded (it's "true"), it returns zero. If the comparison (or whatever operation it carries out) fails (it's "false"), it returns a non-zero exit-status.
if keyword takes a utility and acts on its exit-status. If the utility returns a zero exit-status, it takes the default branch, otherwise it takes the
if test 4 -eq 3; then echo 4 is 3 else echo 4 is not 3 fi
if can take any utility:
if grep -q 'secret' file.txt; then echo file.txt contains secret else echo file.txt does not contain secret fi
if mkdir mydir; then echo created directory mydir else echo failed to create directory mydir fi
0 means the operation was a success and anything other than 0 is an error. So, if
0, then the test was successful and if it is not
0, for example if it is
1, the test failed.
You can see this a bit more clearly perhaps if you run this:
$ number=4 $ if test $number -eq 4; then echo "YES ($?)"; else echo "NO ($?)"; fi YES (0) $ if test $number -lt 2; then echo "YES ($?)"; else echo "NO ($?)"; fi NO (1)
The shell is not
C 0 is false, everything else is true. In the shell 0 is true/success, everything else is false. This is because there are many ways to fail, but one way to succeed.
Specifically from the info page, of test.
Exit status: 0 if the expression is true, 1 if the expression is false, 2 if an error occurred.