Exit Code Number Meaning Example Comments

1     catchall for general errors 
      example: let "var1 = 1/0" 
      miscellaneous errors, such as "divide by zero"

2     misuse of shell builtins, according to Bash documentation   
      Seldom seen, usually defaults to exit code 1

126   command invoked cannot execute   
      permission problem or command is not an executable

127   "command not found"   
      possible problem with $PATH or a typo

128   invalid argument to exit 
      example: exit 3.14159 
      exit takes only integer args in the range 0 - 255

128+n fatal error signal "n" 
      example: kill -9 $PPID of script 
      $? returns 137 (128 + 9)

130   script terminated by Control-C   
      Control-C is fatal error signal 2, (130 = 128 + 2, see above)

255*  exit status out of range 
      example: exit -1 
      exit takes only integer args in the range 0 - 255

According to the table, exit codes 1 - 2, 126 - 165, and 255 [1] 
have special meanings, and should therefore be avoided as user-
specified exit parameters. Ending a script with exit 127 would 
certainly cause confusion when troubleshooting (is the error a 
"command not found" or a user-defined one?). However, many scripts 
use an exit 1 as a general bailout upon error. Since exit code 1 
signifies so many possible errors, this might not add any additional 
ambiguity, but, on the other hand, it probably would not be very 
informative either.

07252003

[[added to wiki.robotz.com 5/22/2007]]