[bug #68650] HISTFILE truncation on open disrespects timestamps

URL:
  <https://savannah.gnu.org/bugs/?68650>

                 Summary: HISTFILE truncation on open disrespects timestamps
                   Group: The GNU Bourne-Again SHell
               Submitter: ilya_the_human
               Submitted: Wed 26 Aug 2026 03:40:59 PM UTC
                Category: None
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Unlocked


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Follow-up Comments:


-------------------------------------------------------
Date: Wed 26 Aug 2026 03:40:59 PM UTC By: Ilya <ilya_the_human>
History file is supposed to be truncated by HISTFILESIZE _entries_, not lines.
But this does not work on shell open. This bug makes combination of positive
HISTFILESIZE together with HISTTIMEFORMAT completely unusable

Demonstration: let's fill the history with HISTFILESIZE entries with
timestamps
```
[ilya@arch ~]$  cat .bashrc
[[ $- != *i* ]] && return
HISTCONTROL=ignoreboth
HISTSIZE=5
HISTFILESIZE=5
HISTTIMEFORMAT="%c "
[ilya@arch ~]$  history
[ilya@arch ~]$  cat .bash_history 
[ilya@arch ~]$ 1
bash: 1: command not found
[ilya@arch ~]$ 2
bash: 2: command not found
[ilya@arch ~]$ 3
bash: 3: command not found
[ilya@arch ~]$ 4
bash: 4: command not found
[ilya@arch ~]$ 5
bash: 5: command not found
[ilya@arch ~]$  history
    1  Wed 26 Aug 2026 19:25:59 +04 1
    2  Wed 26 Aug 2026 19:26:00 +04 2
    3  Wed 26 Aug 2026 19:26:00 +04 3
    4  Wed 26 Aug 2026 19:26:00 +04 4
    5  Wed 26 Aug 2026 19:26:01 +04 5
[ilya@arch ~]$  exit
```
After exit we can observe the following contents of .bash_history. Everything
is correct and as expected:
```
#1787757959
1
#1787757960
2
#1787757960
3
#1787757960
4
#1787757961
5
```

But as soon as we open another shell instance, history file gets truncated to
5 lines, not entries! 
```
[ilya@arch ~]$  cat .bash_history
3
#1787757960
4
#1787757961
5
[ilya@arch ~]$  history
    1  Wed 26 Aug 2026 19:27:26 +04 3
    2  Wed 26 Aug 2026 19:26:00 +04 4
    3  Wed 26 Aug 2026 19:26:01 +04 5
```
From what I see from the code, this is because HISTTIMEFORMAT is read with
`sv_histtimefmt` on variables.c:682. Which happens before .bashrc loading! And
while the neighboring HISTCONTROL and HISTIGNORE are read one more time
elsewhere, HISTTIMEFORMAT is not

Possible fix: looks like this one cannot be fixed as easily, so I'll write a
fix as soon as this is confirmed to be an undesirable bug

P.S. not sure about GNU LLM policy, but just in case - I've not used ai for
finding the issues, fixing them, or for writing bug reports







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