6 SC2076

Joachim Ansorg edited this page 2021-11-12 19:28:53 +01:00

Table of Contents

• Don't quote rhs of =~, it'll match literally rather than as a regex.
• Problematic code:
• Correct code:
• Rationale:
• Exceptions:
• Compatibility:

Don't quote rhs of =~, it'll match literally rather than as a regex.

Problematic code:

[[ $foo =~ "^fo+ bar$" ]]

Correct code:

[[ $foo =~ ^fo+\ bar$ ]]

Rationale:

Quotes on the right hand side of =~ can be used to match literally, so that [[ $1 =~ ^"$2".* ]] works even if $2 contains regex metacharacters. This mirrors the behavior of globs, [[ $1 = "$2"* ]].

This also means that the problematic code tries to match literal carets and plus signs instead of interpreting them as regular expression matchers. To match as a regex, the regex metacharacters it must be unquoted. Literal parts of the expression can be quoted with double or single quotes, or escaped.

Exceptions:

If you do want to match literally just to do a plain substring search, e.g. [[ $foo =~ "bar" ]], you could ignore this message, but consider using a more canonical glob match instead: [[ $foo == *"bar"* ]].

Compatibility:

• In Bash 3.2 and newer with shopt compat31 disabled (the default), quoted patterns are literal whereas unquoted patterns are parsed for regex metacharacters.
• In Bash 3.2 and newer with shopt compat31 enabled, quoted and unquoted patterns match identically.
• In Bash 3.1 quoted and unquoted patterns match identically.

See http://stackoverflow.com/questions/218156/bash-regex-with-quotes

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