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27.7 Read-Only Buffers

If a buffer is read-only, then you cannot change its contents, although you may change your view of the contents by scrolling and narrowing.

Read-only buffers are used in two kinds of situations:

  • A buffer visiting a write-protected file is normally read-only.

    Here, the purpose is to inform the user that editing the buffer with the aim of saving it in the file may be futile or undesirable. The user who wants to change the buffer text despite this can do so after clearing the read-only flag with C-x C-q.

  • Modes such as Dired and Rmail make buffers read-only when altering the contents with the usual editing commands would probably be a mistake.

    The special commands of these modes bind buffer-read-only to nil (with let) or bind inhibit-read-only to t around the places where they themselves change the text.

variable buffer-read-only

This buffer-local variable specifies whether the buffer is read-only. The buffer is read-only if this variable is non-nil. However, characters that have the inhibit-read-only text property can still be modified. See inhibit-read-only.

variable inhibit-read-only

If this variable is non-nil, then read-only buffers and, depending on the actual value, some or all read-only characters may be modified. Read-only characters in a buffer are those that have a non-nil read-only text property. See Special Properties, for more information about text properties.

If inhibit-read-only is t, all read-only character properties have no effect. If inhibit-read-only is a list, then read-only character properties have no effect if they are members of the list (comparison is done with eq).

command read-only-mode \&optional arg

This is the mode command for Read Only minor mode, a buffer-local minor mode. When the mode is enabled, buffer-read-only is non-nil in the buffer; when disabled, buffer-read-only is nil in the buffer. The calling convention is the same as for other minor mode commands (see Minor Mode Conventions).

This minor mode mainly serves as a wrapper for buffer-read-only; unlike most minor modes, there is no separate read-only-mode variable. Even when Read Only mode is disabled, characters with non-nil read-only text properties remain read-only. To temporarily ignore all read-only states, bind inhibit-read-only, as described above.

When enabling Read Only mode, this mode command also enables View mode if the option view-read-only is non-nil. See Miscellaneous Buffer Operations in The GNU Emacs Manual. When disabling Read Only mode, it disables View mode if View mode was enabled.

function barf-if-buffer-read-only \&optional position

This function signals a buffer-read-only error if the current buffer is read-only. If the text at position (which defaults to point) has the inhibit-read-only text property set, the error will not be raised.

See Using Interactive, for another way to signal an error if the current buffer is read-only.