Diff for "BashFAQ/066"

Differences between revisions 14 and 15

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
   if [[ $var == @(foo|bar|more) ]]; then
      ...
   fi

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

# bash/ksh93

[[ -v BASH_VERSION ]] && shopt -s extglob

# usage: pmatch string pattern [ pattern ... ]
function any {
    [[ -n $1 ]] || return
    typeset pat match=$1
    shift

    for pat; do
        [[ $match == $pat ]] && return
    done

    return 1
}

var='foo bar'
if any "$var" '@(bar|baz)' foo\* blarg; then
    echo 'var matched at least one of the patterns!'
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...
    [[ $var == !(!(foo)|!(bar)|!(more)) ]] && ...

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

CategoryShell

-  ⇤ ← 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).
+   ← Revision 15 as of 2015-06-20 07:58:04 → ⇥
  Size: 1525
  Editor: ormaaj
  Comment: Eliminate `while shift'
-Deletions are marked like this.
+Additions are marked like this.
 Line 7:
-   case "$var" in
+   case $var in
 Line 15:
-   ${BASH_VERSION+shopt -s extglob}
-Line 23:
+Line 22:
-    # bash/ksh93/zsh (w/ emulate ksh)
+#!/usr/bin/env bash
# bash/ksh93
 Line 25:
-    # usage: pmatch string pattern [ pattern ... ]
    function pmatch {
        ${1+typeset x=}"${1-false}" &&
        while command shift; do
            [[ $x == $1 ]] && return
        done 2>/dev/null
        return 1
    }
+[[ -v BASH_VERSION ]] && shopt -s extglob
-Line 34:
+Line 27:
-    var='foo bar'
    if pmatch "$var" foo bar baz foo\* blarg; then
        : ...
    fi
+# usage: pmatch string pattern [ pattern ... ]
function any {
    [[ -n $1 ]] || return
    typeset pat match=$1
    shift

    for pat; do
        [[ $match == $pat ]] && return
    done

    return 1
}

var='foo bar'
if any "$var" '@(bar|baz)' foo\* blarg; then
    echo 'var matched at least one of the patterns!'
fi
-Line 51:
+Line 58:
-    ${BASH_VERSION+shopt -s extglob}