Member Avatar for professor123

how can you use the HISTORY command in UNIX or is there an Alternative command to view your previous unix commands.

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The replies already cover the basics: shows simple filtering, pasted the builtin help, notes which shells implement it, and called out size and duplicate controls. The following practical additions fill gaps often encountered later.

Interactive search and quick edits are often fastest. Reverse incremental search (Ctrl+R) finds recent commands by substring; accept a match to run it or use the right-arrow to drop it onto the prompt for editing. The fc builtin opens the previous command in $EDITOR for quick corrections and re-execution. History expansion shortcuts (for example repeating the last command or reusing the last argument) save typing for small edits.

A common, practical Bash setup that keeps longer, timestamped history and shares entries between concurrent terminals:

# add to ~/.bashrc (Bash)
export HISTSIZE=20000
export HISTFILESIZE=200000
export HISTCONTROL=ignoredups:ignorespace
export HISTTIMEFORMAT="%F %T "
shopt -s histappend
PROMPT_COMMAND='history -a; history -n'

This preserves long history, timestamps entries, avoids duplicate and leading-space entries, appends rather than overwrites history, and reloads new lines from other shells. After editing, source the file or start a new shell to apply changes.

Troubleshooting/safety notes: if entries are missing, verify that $HISTFILE points to a writable file and that history is enabled (set -o history for interactive shells). Sensitive data (passwords, keys) should not be typed directly into shells—HISTCONTROL=ignorespace helps avoid accidentally recording commands that begin with a space but is not a security guarantee. These points extend and complement the earlier answers from , , , and .

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Member Avatar for dcdruck

What information are you trying to get that you aren't getting from history? The history command lists all of the commands that have been executed by your user account. If you are looking for a particular command or commands, you can pipe history to grep to filter out what you are looking for.

For example, to see all commands containing the string 'mysql': history | grep mysql

Member Avatar for DavidB

The built-in help function offers a lot of information about how to use the history command too. Here is what I got when I ran the help command on history:

help history
history: history [-c] [-d offset] [n] or history -anrw [filename] or history -ps
 arg [arg...]
    Display or manipulate the history list.

    Display the history list with line numbers, prefixing each modified
    entry with a `*'.  An argument of N lists only the last N entries.

    Options:
      -c        clear the history list by deleting all of the entries
      -d offset delete the history entry at offset OFFSET.

      -a        append history lines from this session to the history file
      -n        read all history lines not already read from the history file
      -r        read the history file and append the contents to the history
        list
      -w        write the current history to the history file
        and append them to the history list

      -p        perform history expansion on each ARG and display the result
        without storing it in the history list
      -s        append the ARGs to the history list as a single entry

#
    if $HISTFILE has a value, that is used, else ~/.bash_history.

    If the $HISTTIMEFORMAT variable is set and not null, its value is used
    as a format string for strftime(3) to print the time stamp associated
    with each displayed history entry.  No time stamps are printed otherwise.

    Exit Status:
    Returns success unless an invalid option is given or an error occurs.

And an Internet search turns up several web pages with additional information, for example, the following:

Click Here

Hope this helps.

Member Avatar for ammonsutherland

'history' is a bash function built into the shell. If your unix system has bash you should be able to simply run bash and then have access to it. Ksh also implements this.

Member Avatar for rubberman

There is an environment variable HISTSIZE that specifies the number of commands that history will save. I'm not sure what the default is, but I have mine set to 1000, so I have access to the last 1000 shell commands. You can also set the HISTCONTROL=ignoredups which will keep you from seeing duplicate commands in your history - a common occurance.

This works for the bash shell. Unix systems often use the Korn or C shells. They have different options to set these limits.

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