An event designator is a reference to a command line entry in the history list.

!

Start a history substitution, except when followed by a blank, newline, = or (.

!n

Refer to command line n.

!-n

Refer to the current command line minus n.

!!

Refer to the previous command. This is a synonym for `!-1'.

!string

Refer to the most recent command starting with string.

!?string[?]

Refer to the most recent command containing string. The trailing ? may be omitted if string is followed immediately by a newline.

d^ustring1d^ustring2d^u

Quick substitution. Repeat the last command, replacing string1 with string2. Equivalent to ``!!:s/string1/string2/'' (see Modifiers below).

!#

The entire command line typed so far.

Word designators are used to select desired words from the event. A : separates the event specification from the word designator. It may be omitted if the word designator begins with a ^, $, *, -, or %. Words are numbered from the beginning of the line, with the first word being denoted by 0 (zero). Words are inserted into the current line separated by single spaces.

0 (zero)

The zeroth word. For the shell, this is the command word.

n

The nth word.

^

The first argument. That is, word 1.

$

The last argument.

%

The word matched by the most recent `?string?' search.

x-y

A range of words; `-y' abbreviates `0-y'.

*

All of the words but the zeroth. This is a synonym for `1-$'. It is not an error to use * if there is just one word in the event; the empty string is returned in that case.

x*

Abbreviates x-$.

x-

Abbreviates x-$ like x*, but omits the last word.

If a word designator is supplied without an event specification, the previous command is used as the event.

After the optional word designator, there may appear a sequence of one or more of the following modifiers, each preceded by a `:'.

h

Remove a trailing file name component, leaving only the head.

t

Remove all leading file name components, leaving the tail.

r

Remove a trailing suffix of the form .xxx, leaving the basename.

e

Remove all but the trailing suffix.

p

Print the new command but do not execute it.

q

Quote the substituted words, escaping further substitutions.

x

Quote the substituted words as with q, but break into words at blanks and newlines.

s/old/new/

Substitute new for the first occurrence of old in the event line. Any delimiter can be used in place of /. The final delimiter is optional if it is the last character of the event line. The delimiter may be quoted in old and new with a single backslash. If & appears in new, it is replaced by old. A single backslash will quote the &. If old is null, it is set to the last old substituted, or, if no previous history substitutions took place, the last string in a !?string[?] search.

&

Repeat the previous substitution.

g

Cause changes to be applied over the entire event line. This is used in conjunction with `:s' (e.g., `:gs/old/new/') or `:&'. If used with `:s', any delimiter can be used in place of /, and the final delimiter is optional if it is the last character of the event line. An a may be used as a synonym for g.

G

Apply the following `s' modifier once to each word in the event line.

The programmer using the History library has available functions for remembering lines on a history list, associating arbitrary data with a line, removing lines from the list, searching through the list for a line containing an arbitrary text string, and referencing any line in the list directly. In addition, a history expansion function is available which provides for a consistent user interface across different programs.

The user using programs written with the History library has the benefit of a consistent user interface with a set of well-known commands for manipulating the text of previous lines and using that text in new commands. The basic history manipulation commands are identical to the history substitution provided by bash.

If the programmer desires, he can use the Readline library, which includes some history manipulation by default, and has the added advantage of command line editing.

Before declaring any functions using any functionality the History library provides in other code, an application writer should include the file in any file that uses the History library's features. It supplies extern declarations for all of the library's public functions and variables, and declares all of the public data structures.

The history list is an array of history entries. A history entry is declared as follows:

typedef struct _hist_entry {
  char *line;
  char *timestamp;
  histdata_t data;
} HIST_ENTRY;


The history list itself might therefore be declared as

The state of the History library is encapsulated into a single structure:

/*
 * A structure used to pass around the current state of the history.
 */
typedef struct _hist_state {
  HIST_ENTRY **entries; /* Pointer to the entries themselves. */
  int offset;           /* The location pointer within this array. */
  int length;           /* Number of elements within this array. */
  int size;             /* Number of slots allocated to this array. */
  int flags;
} HISTORY_STATE;


If the flags member includes HS_STIFLED, the history has been
stifled.

This section describes functions used to initialize and manage the state of the History library when you want to use the history functions in your program.

Begin a session in which the history functions might be used. This initializes the interactive variables.

Return a structure describing the current state of the input history.

Set the state of the history list according to state.

These functions manage individual entries on the history list, or set parameters managing the list itself.

Place string at the end of the history list. The associated data field (if any) is set to NULL.

Change the time stamp associated with the most recent history entry to string.

Remove history entry at offset which from the history. The removed element is returned so you can free the line, data, and containing structure.

Free the history entry histent and any history library private data associated with it. Returns the application-specific data so the caller can dispose of it.

Make the history entry at offset which have line and data. This returns the old entry so the caller can dispose of any application-specific data. In the case of an invalid which, a NULL pointer is returned.

Clear the history list by deleting all the entries.

Stifle the history list, remembering only the last max entries.

Stop stifling the history. This returns the previously-set maximum number of history entries (as set by stifle_history()). history was stifled. The value is positive if the history was stifled, negative if it wasn't.

Returns non-zero if the history is stifled, zero if it is not.

These functions return information about the entire history list or individual list entries.

Return a NULL terminated array of HIST_ENTRY * which is the current input history. Element 0 of this list is the beginning of time. If there is no history, return NULL.

Returns the offset of the current history element.

Return the history entry at the current position, as determined by where_history(). If there is no entry there, return a NULL pointer.

Return the history entry at position offset, starting from history_base. If there is no entry there, or if offset is greater than the history length, return a NULL pointer.

Return the time stamp associated with the history entry passed as the argument.

Return the number of bytes that the primary history entries are using. This function returns the sum of the lengths of all the lines in the history.

These functions allow the current index into the history list to be set or changed.

Set the current history offset to pos, an absolute index into the list. Returns 1 on success, 0 if pos is less than zero or greater than the number of history entries.

Back up the current history offset to the previous history entry, and return a pointer to that entry. If there is no previous entry, return a NULL pointer.

Move the current history offset forward to the next history entry, and return the a pointer to that entry. If there is no next entry, return a NULL pointer.

These functions allow searching of the history list for entries containing a specific string. Searching may be performed both forward and backward from the current history position. The search may be anchored, meaning that the string must match at the beginning of the history entry.

Search the history for string, starting at the current history offset. If direction is less than 0, then the search is through previous entries, otherwise through subsequent entries. If string is found, then the current history index is set to that history entry, and the value returned is the offset in the line of the entry where string was found. Otherwise, nothing is changed, and a -1 is returned.

Search the history for string, starting at the current history offset. The search is anchored: matching lines must begin with string. If direction is less than 0, then the search is through previous entries, otherwise through subsequent entries. If string is found, then the current history index is set to that entry, and the return value is 0. Otherwise, nothing is changed, and a -1 is returned.

Search for string in the history list, starting at pos, an absolute index into the list. If direction is negative, the search proceeds backward from pos, otherwise forward. Returns the absolute index of the history element where string was found, or -1 otherwise.

The History library can read the history from and write it to a file. This section documents the functions for managing a history file.

Add the contents of filename to the history list, a line at a time. If filename is NULL, then read from ~/.history. Returns 0 if successful, or errno if not.

Read a range of lines from filename, adding them to the history list. Start reading at line from and end at to. If from is zero, start at the beginning. If to is less than from, then read until the end of the file. If filename is NULL, then read from ~/.history. Returns 0 if successful, or errno if not.

Write the current history to filename, overwriting filename if necessary. If filename is NULL, then write the history list to ~/.history. Returns 0 on success, or errno on a read or write error.

Append the last nelements of the history list to filename. If filename is NULL, then append to ~/.history. Returns 0 on success, or errno on a read or write error.

Truncate the history file filename, leaving only the last nlines lines. If filename is NULL, then ~/.history is truncated. Returns 0 on success, or errno on failure.

These functions implement history expansion.

Expand string, placing the result into output, a pointer to a string. Returns:

0

If no expansions took place (or, if the only change in the text was the removal of escape characters preceding the history expansion character);

1

if expansions did take place;

-1

if there was an error in expansion;

2

if the returned line should be displayed, but not executed, as with the :p modifier. If an error ocurred in expansion, then output contains a descriptive error message.

Returns the text of the history event beginning at string + *cindex. *cindex is modified to point to after the event specifier. At function entry, cindex points to the index into string where the history event specification begins. qchar is a character that is allowed to end the event specification in addition to the ``normal'' terminating characters.

Return an array of tokens parsed out of string, much as the shell might. The tokens are split on the characters in the history_word_delimiters variable, and shell quoting conventions are obeyed.

Extract a string segment consisting of the first through last arguments present in string. Arguments are split using history_tokenize().

This section describes the externally-visible variables exported by the GNU History Library.

The logical offset of the first entry in the history list.

The number of entries currently stored in the history list.

The maximum number of history entries.  This must be changed using
stifle_history().

If non-zero, timestamps are written to the history file, so they can be
preserved between sessions.  The default value is 0, meaning that
timestamps are not saved.

The character that introduces a history event.  The default is !.
Setting this to 0 inhibits history expansion.

The character that invokes word substitution if found at the start of
a line.  The default is ^.

During tokenization, if this character is seen as the first character
of a word, then it and all subsequent characters up to a newline are
ignored, suppressing history expansion for the remainder of the line.
This is disabled by default.

The characters that separate tokens for history_tokenize().
The default value is " \t\n()<>;&|".

The list of characters which inhibit history expansion if found immediately
following history_expansion_char.  The default is space, tab, newline,
\r, and =.

The list of additional characters which can delimit a history search
string, in addition to space, tab, : and ? in the case of
a substring search.  The default is empty.

If non-zero, single-quoted words are not scanned for the history expansion
character.  The default value is 0.

This should be set to the address of a function that takes two arguments:
a char * (string)
and an int index into that string (i).
It should return a non-zero value if the history expansion starting at
string[i] should not be performed; zero if the expansion should
be done.
It is intended for use by applications like bash that use the history
expansion character for additional purposes.
By default, this variable is set to NULL.