Shell Notes
References:
Handling Empty Variables
param |
Set and Not Null | Set But Null | Unset |
|---|---|---|---|
${param:-word} |
substitute param |
substitute word |
substitute word |
${param-word} |
substitute param |
substitute null | substitute word |
${param:=word} |
substitute param |
assign word |
assign word |
${param=word} |
substitute param |
substitute null | assign word |
${param:?word} |
substitute param |
error, exit | error, exit |
${param?word} |
substitute param |
substitute null | error, exit |
${param:+word} |
substitute word |
substitute null | substitute null |
${param+word} |
substitute word |
substitute word |
substitute null |
Adding Timestamps
Use ts command. ts -i for incremental time stamps. ts -s for time since
start.