I came across a shell script where
echo $? was used. What does this mean . How can we use this in a shell script. Are there any references for this.
see the example here
[root@localhost ~]# jk -bash: jk: command not found [root@localhost ~]# echo $? 1 [root@localhost ~]# pwd /root [root@localhost ~]# echo $? 0 [root@localhost ~]#
At first you are getting 1 because command is wrong And second time you are getting 0 because command was successful
There is no command called
$? returns the result of the last run command in a bash (and probably other) shell.
From http://tldp.org/LDP/abs/html/exit-status.html example 6-1:
#!/bin/bash echo hello echo $? # Exit status 0 returned because command executed successfully. lskdf # Unrecognized command. echo $? # Non-zero exit status returned -- command failed to execute. echo exit 113 # Will return 113 to shell. # To verify this, type "echo $?" after script terminates. # By convention, an 'exit 0' indicates success, #+ while a non-zero exit value means an error or anomalous condition. # See the "Exit Codes With Special Meanings" appendix.