Declare and assign separately to avoid masking return values. Open
export SRCROOT=`pwd`
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Declare and assign separately to avoid masking return values.
Problematic code:
export foo="$(mycmd)"
Correct code:
foo=$(mycmd)
export foo
Rationale:
In the original code, the return value of mycmd
is ignored, and export
will instead always return true. This may prevent conditionals, set -e
and traps from working correctly.
When first marked for export and assigned separately, the return value of the assignment will be that of mycmd
. This avoids the problem.
Exceptions:
If you intend to ignore the return value of an assignment, you can either ignore this warning or use
foo=$(mycmd) || true
export foo
Shellcheck does not warn about export foo=bar
because bar
is a literal and not a command substitution with an independent return value. It also does not warn about local -r foo=$(cmd)
, where declaration and assignment must be in the same command.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Use ./*glob* or -- *glob* so names with dashes won't become options. Open
open *.xcodeproject
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Use ./*glob* or -- *glob* so names with dashes won't become options.
Problematic code:
rm *
Correct code:
rm ./*
or
rm -- *
Rationale
Since files and arguments are strings passed the same way, programs can't properly determine which is which, and rely on dashes to determine what's what.
A file named -f
(touch -- -f
) will not be deleted by the problematic code. It will instead be interpreted as a command line option, and rm
will even report success.
Using ./*
will instead cause the glob to be expanded into ./-f
, which no program will treat as an option.
Similarly, --
by convention indicates the end of options, and nothing after it will be treated like flags (except for some programs possibly still special casing -
as e.g. stdin).
Note that changing *
to ./*
in GNU Tar parameters will add ./
prefix to path names in the created archive. This may cause subtle problems (eg. to search for a specific file in archive, the ./
prefix must be specified as well). So using -- *
is a safer fix for GNU Tar commands.
For more information, see "Filenames and Pathnames in Shell: How to do it Correctly".
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Use $(..) instead of legacy ..
. Open
export SRCROOT=`pwd`
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Use $(STATEMENT) instead of legacy `STATEMENT`
Problematic code
echo "Current time: `date`"
Correct code
echo "Current time: $(date)"
Rationale
Backtick command substitution `STATEMENT`
is legacy syntax with several issues.
- It has a series of undefined behaviors related to quoting in POSIX.
- It imposes a custom escaping mode with surprising results.
- It's exceptionally hard to nest.
$(STATEMENT)
command substitution has none of these problems, and is therefore strongly encouraged.
Exceptions
None.
See also
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.