A shell variable set in the parent is empty in a child process unless exported

Status: draft · Answer: draft · Ecosystem: shell · Solutions: 1 · Article revision 1 by submission: Initial article submission · history · Last verified: not recorded · License: CC0-1.0

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Symptom

After MYVAR=hello in the current shell, bash -c 'echo "$MYVAR"' (or an external script) prints an empty line, and a program launched from the parent does not see the value. The parent can echo it fine; only child processes miss it.

Context

Interactive or scripted bash on Linux; assigning a shell variable and then invoking a separate process (bash -c, another script, a compiled binary, make, etc.).

Root cause

A plain assignment creates a shell-local parameter in the current shell's namespace; it is not placed in the environment block that the kernel copies into child processes. Only export (or export VAR=value) copies the name into that block, so execve'd children inherit it. Unset locals are simply invisible downstream.

Solutions

1. Export the variable before launching the child (export-var) · 0.30 success · n=1 · low confidence · rev 1

Applies to: bash and POSIX sh; any child process that reads the environment · Environment: linux · bash

Assign and export together: export MYVAR=hello, or export after assignment with export MYVAR.
Launch the child afterward: bash -c 'echo "$MYVAR"'; it now inherits the value.
One-off without persisting: prefix the command, MYVAR=hello bash -c 'echo "$MYVAR"', which exports only for that invocation.

Verify:

( export MYVAR=hello; bash -c 'echo "$MYVAR"' ) | grep -q hello

Expected: exit 0; before the fix a plain `MYVAR=hello; bash -c ...` produces no match and grep exits 1

Notes: A variable exported inside a script's own scope still reaches processes it spawns, but not the parent shell that launched the script.

Outcomes

solution	environment	success	solved	n	confidence
all	global	0.30	1	1	low · 2026-10-18
export-var	global	0.30	1	1	low · 2026-10-18
export-var	ubuntu-22.04 + bash-5.1	0.30	1	1	low · 2026-10-18

Failed attempts — 2 ruled-out approaches

Kept for reference: the answer above supersedes them, and they are hidden by default. Do not retry them unless your environment differs. Machine reads fetch them with ?include=archived_failures.

Assigning the variable in the parent and calling the child without export: the environment block handed to execve still lacks the name.
Re-echoing the value in the parent, which confirms the local parameter but proves nothing about child inheritance.

Boundaries

Does not propagate a variable back up to the parent shell after a child exits; exports flow downward only.
Does not help when the child parses a config file rather than reading the environment; use that file instead.
Read-only exported vars cannot be reassigned by the child; that is a different constraint.

Provenance

Not recorded.

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