3.3.3. Finding files
3.3.3.1. Using shell features
In the example on moving files we already saw how the shell can manipulate multiple files at once. In that example, the shell finds out automatically what the user means by the requirements between the square braces "[" and "]" . The shell can substitute ranges of numbers and upper or lower case characters alike. It also substitutes as many characters as you want with an asterisk, and only one character with a question mark.
All sorts of substitutions can be used simultaneously; the shell is very logical about it. The Bash shell, for instance, has no problem with expressions like ls dirname/*/*/*[2-3] .
In other shells, the asterisk is commonly used to minimize the efforts of typing: people would enter cd dir* instead of cd directory . In Bash however, this is not necessary because the GNU shell has a feature called file name completion. It means that you can type the first few characters of a command (anywhere) or a file (in the current directory) and if no confusion is possible, the shell will find out what you mean. For example in a directory containing many files, you can check if there are any files beginning with the letter A just by typing ls A and pressing the Tab key twice, rather than pressing Enter . If there is only one file starting with "A" , this file will be shown as the argument to ls (or any shell command, for that matter) immediately.
3.3.3.2. Which
A very simple way of looking up files is using the which command, to look in the directories listed in the user's search path for the required file. Of course, since the search path contains only paths to directories containing executable programs, which doesn't work for ordinary files. The which command is useful when troubleshooting "Command not Found" problems. In the example below, user tina can't use the acroread program, while her colleague has no troubles whatsoever on the same system. The problem is similar to the PATH problem in the previous part: Tina's colleague tells her that he can see the required program in /opt/acroread/bin , but this directory is not in her path:
tina:~> which acroread
/usr/bin/which: no acroread in (/bin:/usr/bin:/usr/bin/X11)
The problem can be solved by giving the full path to the command to run, or by re-exporting the content of the PATH variable:
tina:~> export PATH=$PATH:/opt/acroread/bin
tina:~> echo $PATH
/bin:/usr/bin:/usr/bin/X11:/opt/acroread/bin
Using the which command also checks to see if a command is an alias for another command:
gerrit:~> which -a ls
ls is aliased to 'ls -F --color=auto'
ls is /bin/ls
3.3.3.3. Find and locate
These are the real tools, used when searching other paths beside those listed in the search path. The find tool, known from UNIX, is very powerful, which may be the cause of a somewhat more difficult syntax. GNU find , however, deals with the syntax problems. This command not only allows you to search file names, it can also accept file size, date of last change and other file properties as criteria for a search. The most common use is for finding file names:
find <path> -name <searchstring>
This can be interpreted as "Look in all files and subdirectories contained in a given path, and print the names of the files containing the search string in their name" (not in their content).
Another application of find is for searching files of a certain size, as in the example below, where user peter wants to find all files in the current directory or one of its subdirectories, that are bigger than 5 MB:
peter:~> find . -size
* License
