When you type your own -exec parameters, be sure to include a space before \;. Otherwise, you might see an error such as missing argument to `-exec'.
Do you see now why some people think the find command is scary? Many people learn just enough about find to be able to use it in a very basic way, but we hope you will see how much it can do if you give it a chance.
Searches for a String in Input with grep
The grep command, like find, is an incredibly powerful search tool in the right hands. Unlike find, though, grep processes any text, whether in files, or just in standard input.
The basic use of grep is this:
$ grep "some text" *
That query searches all files in the current directory (but not subdirectories) for the string some text and prints matching lines along with the name of the file. To enable recursive searching in subdirectories, use the -r parameter, like this:
$ grep -r "some text" *
Each time a string is matched within a file, the filename and the match are printed. If a file contains multiple matches, each of the matches is printed. You can alter this behavior with the -l parameter (lowercase L), which forces grep to print the name of each file that contains at least one match, without printing the matching text. If a file contains more than one match, it is still printed only once. Alternatively, the -c parameter prints each filename that was searched and includes the number of matches at the end, even if there were no matches.
You have a lot of control when specifying the pattern to search for. You can, as previously, specify a simple string like some text, or you can invert that search by specifying the -v parameter. For example, this returns all the lines of the file myfile.txt that do not contain the word hello:
$ grep -v "hello" myfile.txt
You can also use regular expressions for your search term. For example, you can search myfile.txt for all references to cat, sat, or mat with this command:
$ grep "[cms]at" myfile.txt
Adding the -i parameter to that removes case sensitivity, matching Cat, CAT, MaT, and so on:
$ grep -i [cms]at myfile.txt
The output can also be controlled to some extent with the -n and --color parameters. The first tells grep to print the line number for each match, which is where it appears in the source file. The --color parameter tells grep to color the search terms in the output, which helps them stand out when among all the other text on the line. You choose which color you want, using the GREP_COLOR environment variable: export GREP_COLOR=36 gives you cyan, and export GREP_COLOR=32 gives you lime green.
This next example uses these two parameters to number and color all matches to the previous command:
$ grep -in --color [cms]at myfile.txt
Later you will see how important grep is for piping with other commands.
Paging Through Output with less
The less command enables you to view large amounts of text in a more convenient way than the cat command. For example, your /etc/passwd file is probably more than a screen long, so if you run cat /etc/passwd, you are not able to see what the lines at the top were. Using less /etc/passwd enables you to use the cursor keys to scroll up and down the output freely. Type q to quit and return to the shell.
On the surface, less sounds like a very easy command; however, it has the infamy of being one of the few Linux commands that have a parameter for every letter of the alpha bet. That is, -a does something, -b does something else, -c, -d, -e … -x, -y, -z — they all do things, with some letters even differentiating between upper- and lowercase. Furthermore, these are only the parameters used to invoke less. After you begin viewing your text, even more commands are available to you. Make no mistake — less is a complex beast to master.
Input to less can be divided into two categories: what you type before running less and what you type while running it. The former category is easy, so we start there.
We have already discussed how many parameters less is capable of taking, but they can be distilled down to three that are very usefuclass="underline" -M, -N, and +. Adding -M (this is different from -m!) enables verbose prompting in less. Instead of just printing a colon and a flashing cursor, less prints the filename, the line numbers being shown, the total number of lines, and the percentage of how far you are through the file. Adding -N (again, this is different from -n) enables line numbering.
The last option, +, enables you to pass a command to less for it to execute as it starts. To use this, you first need to know the commands available to you in less, which means we need to move onto the second category of less input: what you type while less is running.
The basic navigation keys are the up, down, left, and right cursors; Home and End (for navigating to the start and end of a file); and Page Up and Page Down. Beyond that, the most common command is /, which initiates a text search. You type what you want to search for and press Enter to have less find the first match and highlight all subsequent matches. Type / again and press Enter to have less jump to the next match. The inverse of that is ?, which searches backward for text. Type ?, enter a search string, and press Enter to go to the first previous match of that string, or just use ? and press Enter to go to the next match preceding the current position. You can use / and ? interchangeably by searching for something with / and then using ? to go backward in the same search.
Searching with / and ? is commonly done with the + command-line parameter from earlier, which passes less a command for execution after the file has loaded. For example, you can tell less to load a file and place the cursor at the first match for the search hello, like this:
$ less +/hello myfile.txt
Or, you can tell it to place the cursor at the last match for the search hello:
$ less +?hello myfile.txt
Beyond the cursor keys, the controls primarily involve typing a number and then pressing a key. For example, to go to line 50, type 50g, or to go to the 75% point of the file, type 75p. You can also place invisible mark points through the file by pressing m and then typing a single letter. Later, while in the same less session, you can press ' (a single quote) and then type the letter, and you will move back to the same position. You can set up to 52 marks, named a-z and A-Z.