Diff for "BashFAQ/066"

Differences between revisions 9 and 14 (spanning 5 versions)

I want to check if [[ $var == foo || $var == bar || $var == more ]] without repeating $var n times.

The portable solution uses case:

   # Bourne
   case "$var" in
      foo|bar|more) ... ;;
   esac

In Bash and ksh, Extended globs can also do this within a [[ command:

   # bash/ksh
   ${BASH_VERSION+shopt -s extglob}
   if [[ $var == @(foo|bar|more) ]]; then
      ...
   fi

Alternatively, you may loop over a list of patterns, checking each individually.

    # bash/ksh93/zsh (w/ emulate ksh)

    # usage: pmatch string pattern [ pattern ... ]
    function pmatch {
        ${1+typeset x=}"${1-false}" &&
        while command shift; do
            [[ $x == $1 ]] && return
        done 2>/dev/null
        return 1
    }

    var='foo bar'
    if pmatch "$var" foo bar baz foo\* blarg; then
        : ...
    fi

For logical conjunction (return true if $var matches all patterns), ksh93 can use the & pattern delimiter.

    # ksh93 only
    [[ $var == @(foo&bar&more) ]] && ...

For shells that support only the ksh88 subset (extglob patterns), you may DeMorganify the logic using the negation sub-pattern operator.

    # bash/ksh88/etc...
    ${BASH_VERSION+shopt -s extglob}
    [[ $var == !(!(foo)|!(bar)|!(more)) ]] && ...

But this is quite unclear and not much shorter than just writing out separate expressions for each pattern.

CategoryShell

-  ⇤ ← Revision 9 as of 2008-11-22 23:08:34 → 
  Size: 1367
  Editor: GreyCat
  Comment: first-line
+   ← Revision 14 as of 2013-01-14 22:03:43 → ⇥
  Size: 1555
  Editor: ormaaj
  Comment: Stupid mksh. Why the does shift throw fatal errors when POSIX doesn't require it to?!? Add "command" workaround (POSIX doesn't require that either, but it works everywhere except mksh).
-Deletions are marked like this.
+Additions are marked like this.
 Line 6:
-   case $var in
+   # Bourne
   case "$var" in
-Line 11:
+Line 12:
-And here's one that uses `=~` (which requires bash 3.0 or higher):
+In Bash and ksh, [[glob|Extended globs]] can also do this within a `[[` command:
-Line 13:
+Line 14:
-   regex='^(foo|bar|more)$'
   if [[ $var =~ $regex ]]; then
+   # bash/ksh
   ${BASH_VERSION+shopt -s extglob}
   if [[ $var == @(foo|bar|more) ]]; then
-Line 19:
+Line 21:
-This one '''only works in bash 3.1''' and '''some 3.2 revisions''' (it is untested in 3.0):
+Alternatively, you may loop over a list of patterns, checking each individually.
-Line 21:
+Line 23:
-   if [[ $var =~ '^(foo|bar|more)$' ]]; then
      ...
   fi
+    # bash/ksh93/zsh (w/ emulate ksh)

    # usage: pmatch string pattern [ pattern ... ]
    function pmatch {
        ${1+typeset x=}"${1-false}" &&
        while command shift; do
            [[ $x == $1 ]] && return
        done 2>/dev/null
        return 1
    }

    var='foo bar'
    if pmatch "$var" foo bar baz foo\* blarg; then
        : ...
    fi
-Line 26:
+Line 40:
-The `=~` operator behavior changes drastically between 3.1 and 3.2, so be careful with it. The above expression is tested to work in bash ''3.1'' and ''3.2.{13,15,17}''; and it doesn't work in ''3.2.0''. 
Please also note that the regexp does not need to be quoted in the 3.2 revisions where it works. --[[redondos]]
+For logical conjunction (return true if `$var` matches all patterns), ksh93 can use the `&` pattern delimiter.
-Line 29:
+Line 42:
-Normally I would never advocate [[BashFAQ/050|sticking code into a variable]] and attempting to use it -- lots of people have ''enormous'' trouble because they try to do that.  In the case of `=~`, though, it seems to be required.  Personally, I'd just stick with the `case`. --GreyCat
+{{{
    # ksh93 only
    [[ $var == @(foo&bar&more) ]] && ...
}}}
-Line 31:
+Line 47:
-The regexp works as long as it is quoted with bash version ''3.00.15(1)-release'' on CentOS4/RHEL4.  I didn't bother checking whether bash is a patched version or not in CentOS4/RHEL4. --ellingsw
+For shells that support only the ksh88 subset (extglob patterns), you may [[http://en.wikipedia.org/wiki/DeMorgan%27s_Law | DeMorganify]] the logic using the negation sub-pattern operator.

{{{
    # bash/ksh88/etc...
    ${BASH_VERSION+shopt -s extglob}
    [[ $var == !(!(foo)|!(bar)|!(more)) ]] && ...
}}}

But this is quite unclear and not much shorter than just writing out separate expressions for each pattern.
----
CategoryShell