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Robust expansion (i.e. crash) of bash variables with a typo

Terminal - Robust expansion (i.e. crash) of bash variables with a typo
set -eu
2010-04-07 11:54:40
User: wipu
Functions: set
8
Robust expansion (i.e. crash) of bash variables with a typo

By default bash expands an unbound variable to an empty string. This can be dangerous, if a critical variable name (a path prefix for example) has a typo. The -u option causes bash to treat this as an error, and the -e option causes it to exit in case of an error. These two together will make your scripts a lot safer against typos.

The default behaviour can be explicitly requested using the ${NAME:-} syntax.

A (less explicit) variation: #!/bin/bash -eu

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Terminal - Alternatives

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What others think

The -e and -u options are POSIX standard, so they should work with any /bin/sh, not just bash.

Comment by inof 210 weeks and 1 day ago

Btw, you need to be careful with commands like grep and find that exit with nonzero when they don't find anything. To make matters worse, failures like these are completely silent. These kinds of commands need to be "guarded" by e.g. adding '|| echo "Nothing found"' or something after them.

IMHO this kind of problem is less dangerous and easier to solve than the problems caused by not using set -eu, though.

Comment by wipu 132 weeks and 4 days ago

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