bash Cookbook

Running Several Commands in Sequence

Problem

You need to run several commands, but some take a while and you don’t want to wait for the last one to finish before issuing the next command.

Solution

There are three solutions to this problem, although the first is rather trivial: just keep typing. A Linux or Unix system is advanced enough to be able to let you type while it works on your previous commands, so you can simply keep typing one command after another.

Another rather simple solution is to type those commands into a file and then tell bash to execute the commands in the file—i.e., a simple shell script.

Assume that we want to run three commands: long, medium, and short, each of whose execution time is reflected in its name. We need to run them in that order, but don’t want to wait around for long to finish before starting the other commands. We could use a shell script (aka batch file). Here’s a primitive way to do that:

$ cat > simple.script
long
medium
short
^D                      # Ctrl-D, not visible
$ bash ./simple.script

The third, and arguably best, solution is to run each command in sequence. If you want to run each program, regardless if the preceding ones fail, separate them with semicolons:

$ long ; medium ; short

If you only want to run the next program if the preceding program worked, and all the programs correctly set exit codes, separate them with double-ampersands:

$ long && medium && short

Discussion

The cat example was just a very primitive way to enter text into a file. We redirect the ...