fix(it2check): Set timeout so read does not hang

[mattmartini]

See GitLab Issue: gnachman/iterm2#12934

Utility it2check hangs when run as root in bash 5.2.21

• iTerm2 version: 3.6.11
• OS version: macOS 26.5 (Tahoe)

Running it2check as root under bash 5.2.21 hangs. Regular users can run this without a problem.

I discovered this issue after upgrading a server from Ubuntu 22.04 (running bash 5.1.16(1)-release) to Ubuntu 24.04 (running bash 5.2.21(1)-release). In my .bash_profile I run it2check to decide how to set some ENV vars. Logging into the upgraded server, sessions hang. I traced the problem to:

It gets stuck at line 50
while read none; do :; done

It seems that there is issue with this in bash.

The fix for the issue is to set a timeout on the read. I also set max chars.

while read -t 0.1 -n 10000 none; do :; done

I am sending a pull request on GitHub with my changes.

My solution was inspired by: clear-stdin-before-reading

Detailed steps to reproduce the problem:

1. login as root
2. run it2check

What happened:
the session hangs with no way out as ctrl-c and other remidies are captured and ignored.

What should have happened:
It returns after assessing if you are running iTerm2.

[gnachman]

Thanks for tracking this down and for the clear write-up.

Two things before this can land:

1. The source of truth for this file is a different repo. OtherResources/Utilities/it2check in this repo is copied in from https://github.com/gnachman/iTerm2-shell-integration, so a change here would get overwritten on the next sync. The fix needs to be made in iTerm2-shell-integration instead (and it will then flow back into this repo).

2. Fractional read -t is not portable to bash < 4.0. The -n 10000 flag is fine, but the fractional -t 0.1 timeout was only added in bash 4.0. The script's shebang is #!/usr/bin/env bash, so it runs under whatever bash is first in PATH, which on a stock macOS box (no Homebrew) is the system /bin/bash 3.2.57. There:

$ /bin/bash -c 'while read -t 0.1 -n 10000 none; do :; done < /dev/null; echo exit=$?'
/bin/bash: line 0: read: 0.1: invalid timeout specification
exit=0

So on bash 3.2 the patched line prints an error to stderr on every run and read fails immediately, meaning the input-drain loop becomes a no-op. The original while read none worked silently there (with stty ... min 0 time 0, read returns at EOF). So as written this trades the bash-5.2 hang for a bash-3.2 regression.

A version-guarded form keeps the fast path where it is available and falls back to the old behavior otherwise:

if [ "${BASH_VERSINFO[0]:-0}" -ge 4 ]; then
  while read -t 0.1 -n 10000 none; do :; done
else
  while read -n 10000 none; do :; done
fi

Could you re-open this against iTerm2-shell-integration with a portable form? Happy to help review it there.

[mattmartini]

George,

I made the pull-request from iTerm2-shell-intergration as you requested.