Return codes and exit statuses

Bash Scripting

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• check the exit status of a command
• make decisions based on that status
• use your own exit statuses

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Exit Status/Return Code

• every command returns an exit status
• integers ranging from 0 to 255
• 0 = success
• non 0 = error
• use for error checking
• have to use man or info for the meaning of the error code

$? contains the return code of the previously executed command

eg

#!/bin/bash
 
HOST="archlinux.org"
ping -c 1 $HOST
 
if [ "$?" -eq "0" ]
then 
	echo "$HOST reachable"
else 
	echo "$HOST unreachable"
fi

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Chaining Commands

• && = AND mkdir /tmp/bak && cp test.txt /tmp/bak
  • only runs $2^{nd}$ command only if $1^{st}$ returns 0
• || = OR cp test.txt /tmp/bak || cp test.txt /tmp
  • only runs $2^{nd}$ command only if $1^{st}$ does not return 0
• ;
  • all commands get executes

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Exit Command

• explicitly define the return code
  • exit 0; ... ; exit 255
• the default value is that of the last command executed

eg

#!/bin/bash
 
HOST="archlinux.org"
ping -c 1 $HOST
 
if [ "$?" -eq "0" ]
then 
	echo "$HOST reachable"
else 
	echo "$HOST unreachable"
	exit 1
fi
exit 0

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