UNIX Tutorial Four
The characters * and ?
The character * is called a wildcard, and will match against none or more character(s) in a file (or directory) name. For example, in your unixstuff directory, type
% ls list*
This will list all files in the current directory starting with list....
% 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.
% 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
There are on-line manuals which gives 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 wc (word count) command, type
% man wc
% whatis wc
gives a one-line description of the command, but omits any information about options etc.
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 copy
||match any number of characters|
||match one character|
||read the online manual page for a command|
||brief description of a command|
||match commands with keyword in their man pages|