Diff for "BashFAQ/066"

Differences between revisions 2 and 14 (spanning 12 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 2 as of 2007-05-24 14:21:15 → 
  Size: 323
  Editor: redondos
  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 1:
-[[Anchor(faq66)]]
+<<Anchor(faq66)>>
 Line 3:
+The portable solution uses `case`:
-Line 4:
+Line 5:
-Here's a portable solution:
 Line 6:
-   case $var in
+   # Bourne
   case "$var" in
-Line 11:
+Line 12:
-And here's one that uses '[[':
+In Bash and ksh, [[glob|Extended globs]] can also do this within a `[[` command:
-Line 13:
+Line 14:
-   if [[ $var =~ foo|bar|more ]]; then
+   # bash/ksh
   ${BASH_VERSION+shopt -s extglob}
   if [[ $var == @(foo|bar|more) ]]; then
-Line 17:
+Line 20:
+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 [[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