====== BASH - Run a program or script - Run a bunch of commands in sequence ======

To run a bunch of commands just put semicolons between the commands:

<code bash>
date ; free; date
</code>

returns:

<code bash>
Thu  4 Feb 13:30:42 GMT 2021
              total        used        free      shared  buff/cache   available
Mem:       65872344     7039056    47427116      929180    11406172    57177400
Swap:        999420           0      999420
Thu  4 Feb 13:30:42 GMT 2021
</code>

<WRAP info>
**NOTE:**  As can be seen the same command can be run multiple times.

Here the **date** command is run twice.
</WRAP>

----


<WRAP alert>
**ALERT**:  Running commands in sequence can be bad.

For example:

<code bash>
cd /foo; rm *
</code>

<WRAP info>
**NOTE:**  The idea here is to erase all the files in directory foo (but not sub-directories; **-r** is needed for that).

But what if the **cd** fails?  Then all the files in the current directory will be erased instead.  Not good!

</WRAP>

Far better to use:

<code bash>
cd /foo && rm *
</code>

<WRAP info>
**NOTE:**  The **&&** is just like in C; this is the **AND** operator.

Nearly all BASH programs return a 0 error status for true and anything else is false.

  * That allows programmers to return an error code for failure and which returns a false.

To test, this rather use the following (which does not include the **rm** for safety).

<code bash>
cd /foo && ls   # Not rm so we don't do anything bad by mistake.
</code>

If /foo exists, the cd command will return 0 which is true.

  * That means the result of the AND could be true and therefore execution continues with the ls.
  * However, if the cd fails, the result will be false.
  * If any input to an AND function is false, the other values does not matter.
  * Therefore, as soon as anything returns false, the whole thing stops.
  * So if there is no /foo, the ls command will not execute at all.

</WRAP>


</WRAP>

----

===== OR =====

There is also an OR operator **||** that quits as soon as anything returns true.

<code bash>
grep "dummy" /etc/passwd || echo No such user
</code>

<WRAP info>
**NOTE:**  Try this command using an actual user instead of dummy to see what is returned when this succeeds.
</WRAP>