2.2 How to search Info documents for specific subjects

The commands which move between and inside nodes allow you to read the entire manual or its large portions. But what if you need to find some information in the manual as fast as you can, and you don't know or don't remember in what node to look for it? This need arises when you use a manual as a reference, or when it is impractical to read the entire manual before you start using the programs it describes.

Info has powerful searching facilities that let you find things quickly. You can search either the manual indices or its text.

Since most subjects related to what the manual describes should be indexed, you should try the index search first. The i command prompts you for a subject and then looks up that subject in the indices. If it finds an index entry with the subject you typed, it goes to the node to which that index entry points. You should browse through that node to see whether the issue you are looking for is described there. If it isn't, type , one or more times to go through additional index entries which match your subject.

The i command finds all index entries which include the string you typed as a substring. For each match, Info shows in the echo area the full index entry it found. Often, the text of the full index entry already gives you enough information to decide whether it is relevant to what you are looking for, so we recommend that you read what Info shows in the echo area before looking at the node it displays.

Since i looks for a substring, you can search for subjects even if you are not sure how they are spelled in the index. For example, suppose you want to find something that is pertinent to commands which complete partial input (e.g., when you type <TAB>). If you want to catch index entries that refer to “complete”, “completion”, and “completing”, you could type icomplet<RET>.

Info documents which describe programs should index the commands, options, and key sequences that the program provides. If you are looking for a description of a command, an option, or a key, just type their names when i prompts you for a topic. For example, if you want to read the description of what the C-f key does, type i C - f <RET>. Here C-f are 3 literal characters `C', `-', and `f', not the “Control-f” command key you type inside Emacs to run the command bound to C-f.

In Emacs, i runs the command Info-index.

If you don't know what manual documents something, try the M-x info-apropos command. It prompts for a string and then looks up that string in all the indices of all the Info documents installed on your system.

The s command allows you to search a whole file for a string. It switches to the next node if and when that is necessary. You type s followed by the string to search for, terminated by <RET>. To search for the same string again, just s followed by <RET> will do. The file's nodes are scanned in the order they are in in the file, which has no necessary relationship to the order that they may be in the tree structure of menus and `next' pointers. But normally the two orders are not very different. In any case, you can always do a b to find out what node you have reached, if the header is not visible (this can happen, because s puts your cursor at the occurrence of the string, not at the beginning of the node).

In Emacs, Meta-s is equivalent to s. That is for compatibility with other GNU packages that use M-s for a similar kind of search command. Both s and M-s run in Emacs the command Info-search.