Diff for "BashFAQ/066"

Differences between revisions 12 and 14 (spanning 2 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 12 as of 2013-01-03 17:46:44 → 
  Size: 838
  Editor: static-74-106-235-64
  Comment:
+   ← 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 14:
-   # bash/ksh -- ksh does not need the shopt
   shopt -s extglob
   if [[ $var = @(foo|bar|more) ]]; then
+   # bash/ksh
   ${BASH_VERSION+shopt -s extglob}
   if [[ $var == @(foo|bar|more) ]]; then
 Line 21:
-Alternatively, the "inarray" function could be used:
+Alternatively, you may loop over a list of patterns, checking each individually.
 Line 23:
-   # usage: inarray NEEDLE HAYSTACK ...
   # returns 0 if NEEDLE is in HAYSTACK, otherwise 1.
   inarray() {
     local n=$1 h
     shift
+    # bash/ksh93/zsh (w/ emulate ksh)
-Line 29:
+Line 25:
-     for n; do
       [[ $n = "$h" ]] && return
     done
     return 1
   }
+    # 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
    }
-Line 35:
+Line 34:
-   if inarray $var foo bar more; then
     ...
   fi
+    var='foo bar'
    if pmatch "$var" foo bar baz foo\* blarg; then
        : ...
    fi
 Line 40:
+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 [[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.