5.4 Run an operating-system command

Use the IOC shell’s system command to run a Linux shell command. An IOC command and an operating-system command use different entry points.

In the generated application root, find the DBD inclusion:
```
grep 'system.dbd' jeonglee_DemoApp/src/Makefile
```
Common_DBDs += system.dbd includes the registrar for system in the application DBD. Support registration makes it available to the IOC.
In an activated Bash terminal, start a soft IOC in a scratch directory:
```
SYSTEM_WORK="$(mktemp -d)"
cd "$SYSTEM_WORK"
softIoc
```
At the IOC prompt, compare these commands:
```
pwd
system pwd
system(pwd)
system("pwd")
```
Each prints the working directory. pwd is an IOC shell command; the other forms invoke the operating system’s pwd through system.
Pass commands containing spaces as one quoted argument:
```
system("mkdir test_folder")
system("test -d test_folder && printf 'directory exists\n'")
```
The second command prints directory exists. An unquoted system mkdir test_folder supplies two arguments to a command that expects one; it does not express the intended shell command.
Stop the soft IOC:
```
exit
```
In the returned Bash shell, inspect the result:
```
ls -ld test_folder
```
The directory exists under SYSTEM_WORK. system uses the IOC process’s account, environment, and current directory.
Leave and remove the scratch directory:
```
cd ~
rm -rf "$SYSTEM_WORK"
```

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