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13
I see these two usage on Ubuntu "command && command" and "command ; command",
e.g. apt-get update && apt-get upgrade
What would differ if I use apt-get update; apt-get upgrade?
I am not asking for this specific usage but in general what is the difference between these two usage?
88
&& is a logical operator. ; is simple sequencing.
In cmd1 && cmd2, cmd2 will only be run if cmd1 exits with a successful return code.
Whereas in cmd1; cmd2, cmd2 will run regardless of the exit status of cmd1 (assuming you haven't set your shell to exit on all failure in your script or something).
On a related note, with cmd1 || cmd2, using the || 'OR' logical operator, cmd2 will only be run if cmd1 fails (returns a non-zero exit code).
These logical operators are sometimes used in scripts in place of a basic if statement. For example,
if [[ -f "$foo" ]]; then mv "$foo" "${foo%.txt}.mkd"; fi
...can be more concisely achieved with:
[[ -f "$foo" ]] && mv "$foo" "${foo%.txt}.mkd"
Etan Reisner
Posted 2013-07-12T15:03:21.833
Reputation: 1 848
I find it a little bit fallacious because from my understanding, successful return code means 0, which, when cast into bool, gives a logical false. So going by the philosophy of Mccarthy evaluation used in most languages, it should immediately return false rather than evaluating (running) the next statement. – Della – 2019-01-10T03:53:10.010
33
command1 && command2
command2 is executed if, and only if, command1 returns an exit status of zero (true). In other words, run command1 and if it is successfull, then run command2.
command1 ; command2
Both command1 and command2 will be executed regardless. The semicolon allows you to type many commands on one line.
Related:
command1 || command2
command2 is executed if, and only if, command1 returns a non-zero exit status. In other words, run command1 successfully or run command2.
&& operator:
$ rm /tmp/filename && echo "File deleted"
; operator:
$ echo "foo" ; echo "bar"
|| operator:
$ cat /tmp/filename 2>/dev/null || echo "Failed to open file"
stderr
Posted 2013-07-12T15:03:21.833
Reputation: 9 300
2Win command-line and batch have the same feature:
& (simple sequencing), && (conditional AND) and || (conditional OR). – Karan – 2013-07-12T16:13:30.7535
See also: Bash Reference Manual – List of commands. In general, there's nothing you can't find in the documentation; it's really worth looking at if you have a question about specific syntax elements.
– slhck – 2013-07-12T17:51:20.3871@Karan And for completeness, bash (linux/Ubuntu) has
||as well. – Izkata – 2013-07-12T19:09:09.857