Fix path export command in source installation guide

[linzhu-dot]

ISAACSIM_PATH is wrong because ${pwd} is empty; only $PWD or $(pwd) or ${PWD} work.

Type of change

• Documentation update

[greptile-apps]

Greptile Summary

This PR fixes a shell syntax error in the source installation guide where ${pwd} was used instead of $(pwd) for command substitution in the export ISAACSIM_PATH instruction.

• Root cause: In bash, ${pwd} attempts to expand a variable named pwd, which is not set (the current-directory variable is PWD, uppercase). This would silently produce an empty string, causing the exported path to be /_build/linux-x86_64/release instead of the intended full path.
• Fix: Replaced ${pwd} with $(pwd), which is correct bash command substitution syntax — it executes the pwd command and substitutes its output inline.
• The change is confined to a single line in the Linux tab of the RST documentation file; the Windows tab already uses the correct equivalent (%cd%) and is unaffected.

Confidence Score: 5/5

• This PR is safe to merge — it corrects a silent shell bug in documentation with no code or runtime impact.
• The change is a one-line documentation fix that corrects a clear bash syntax error (${pwd} → $(pwd)). There are no logic changes, no new dependencies, and no risk of regression. The fix is technically accurate: $(pwd) is standard POSIX command substitution and will correctly expand to the current working directory.
• No files require special attention.

Important Files Changed

Filename	Overview
docs/source/setup/installation/source_installation.rst	Single-line fix replacing invalid ${pwd} variable expansion with correct $(pwd) command substitution for the ISAACSIM_PATH export — change is correct and well-scoped.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[User runs source installation guide] --> B["export ISAACSIM_PATH=..."]
    B --> C{Shell syntax used?}
    C -- "Before fix: \${pwd}" --> D["Variable expansion for 'pwd'\n(undefined variable)"]
    D --> E["ISAACSIM_PATH = '/_build/linux-x86_64/release'\n(empty prefix — broken path)"]
    C -- "After fix: \$(pwd)" --> F["Command substitution:\nruns the pwd command"]
    F --> G["ISAACSIM_PATH = '/home/user/isaaclab/_build/linux-x86_64/release'\n(correct full path)"]
    G --> H["export ISAACSIM_PYTHON_EXE=\${ISAACSIM_PATH}/python.sh"]
    E --> I["export ISAACSIM_PYTHON_EXE fails — path is wrong"]

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