Public bug reported:
bash 5.1.16 (Ubuntu 22.04, package bash 5.1-6ubuntu1.x)
The bash(1) man page states that LINES and COLUMNS are "automatically
set ... in an interactive shell upon receipt of a SIGWINCH". In
practice, both variables are also updated in non-interactive shells
whenever the shell evaluates a command that queries terminal geometry
via ioctl(TIOCGWINSZ).
Reproducer:
cat > /tmp/demo.sh << 'EOF'
#!/bin/bash
LINES=()
LINES+=("hello")
echo "BEFORE: ${LINES[0]}"
ss -tln >/dev/null 2>&1
echo "AFTER: ${LINES[0]}"
EOF
bash /tmp/demo.sh # from a TTY: prints terminal
height
ssh user@host 'bash /tmp/demo.sh' # without -tt: prints "hello"
Expected: behavior consistent with documentation, OR documentation
updated to reflect the actual behavior.
The practical impact is silent corruption of scripts using LINES or
COLUMNS as user-defined variables. The bug only reproduces from a
TTY, so it does not appear in CI, cron, or ssh-without-tty runs,
making it particularly hard to diagnose.
This is upstream behavior, not Ubuntu-specific. Reporting here for
distribution-level visibility; an upstream report has been filed on
[email protected] [link after sending].
ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: bash 5.1-6ubuntu1.x
ProcVersionSignature: Ubuntu 5.15.0-173.x-generic 5.15.x
Uname: Linux 5.15.0-173-generic x86_64
** Affects: bash (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2152122
Title:
[doc] LINES/COLUMNS auto-update in non-interactive shells contradicts
manual
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