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# Bash Error Handling and Safety
## Paranoid mode (`set -e`)
Enable `set -e` so the script exits on any unexpected non-zero status. Temporarily disable it around commands that are allowed to fail.
```bash
set -e
some_function () {
# ... critical code ...
set +e
grep ... || true
local -i ec=$?
set -e
if (( ec != 0 )); then
: # handle expected non-match
fi
}
```
## `pipefail`
Use `set -o pipefail` so the pipeline returns the status of the last command that exited non-zero, not just the last command.
```bash
set -o pipefail
command1 | command2 | command3
```
## `PIPESTATUS`
Capture `PIPESTATUS` into an array immediately after a pipeline to inspect each stage's exit code.
```bash
tar -cf - ./* | ( cd "$dir" && tar -xf - )
return_codes=("${PIPESTATUS[@]}")
if (( return_codes[0] != 0 )); then
echo 'tar failed' >&2
fi
```
## Arithmetic and Comparisons
Use arithmetic evaluation `(( ))` or numeric comparison operators (`-gt`, `-lt`, `-eq`) to avoid unintended lexicographical comparison.
```bash
# Wrong: lexicographical
if [[ "$my_var" > 3 ]]; then
# Right: numeric
if (( my_var > 3 )); then
if [[ "$my_var" -gt 3 ]]; then
```
## Restricted Bash
Use `rbash` as a coarse sandbox for highly constrained environments.
```bash
rbash -c 'echo hi'
```
See `man bash` (RESTRICTED SHELL) for details and caveats.
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