Chapter 4: Filenames and Getting Help

4.1 Wildcards

The characters * and ?

The character * is called a wildcard, and will match against zero or more characters in a file (or directory) name. For example, in your linuxstuff directory, type

$ ls list*

This will list all files in the current directory starting with list

Now try typing

$ ls *list

This will list all files in the current directory ending with list

The character ? will match exactly one character. So ls ?ouse will match files like house and mouse, but not grouse.
Try typing

$ ls ?list

4.2 Filename conventions

We should note here that a directory is merely a special type of file. So the rules and conventions for naming files apply also to directories.

In naming files, characters with special meanings such as / * & % , should be avoided. Also, avoid using spaces within names. The safest way to name a file is to use only alphanumeric characters, that is, letters and numbers, together with _ (underscore) and . (dot).

File names conventionally start with a lower-case letter, and may end with a dot followed by a group of letters indicating the contents of the file. For example, all files consisting of C code may be named with the ending .c, for example, prog1.c . Then in order to list all files containing C code in your home directory, you need only type ls *.c in that directory.

Beware: Some applications give the same name to all the output files they generate.

For example, some compilers, unless given the appropriate option, produce compiled files named a.out. Should you forget to use that option, you are advised to rename the compiled file immediately, otherwise the next such file will overwrite it and it will be lost.

4.3 Getting Help

On-line Manuals

There are on-line manuals which give information about most commands. The manual pages tell you which options a particular command can take, and how each option modifies the behaviour of the command. Type man command to read the manual page for a particular command.

For example, to find out more about the qsub (used to submit jobs to the supercomputer) command, type

$ man qsub

Alternatively

$ whatis qsub

gives a one-line description of the command, but omits any information about options etc.

Apropos

When you are not sure of the exact name of a command,

$ apropos keyword

will give you the commands with keyword in their manual page header. For example, try typing

$ apropos slurm

to learn more about Slurm, the resource manager used to submit jobs to the supercomputer.

Summary

`*`	match zero or more characters
`?`	match exactly one character
`man command`	read the online manual page for a command
`whatis command`	brief description of a command
`apropos keyword`	match commands with keyword in their man pages