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stackbiz
Asked: 2024-06-20 21:06:03 +0800 CST

How to use asterisk (*) in bash array

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I want to stored all command args in an array but it only works when all args have no any (*).

Here is a test without using array:

mkdir -p /tmp/hello
echo "hello" > /tmp/hello/hello.txt
echo "world" > /tmp/hello/world.txt

mkdir -p /tmp/world

# This cp command is success
cp /tmp/hello/* /tmp/world

Now convert the cp command into my_array:

mkdir -p /tmp/hello
echo "hello" > /tmp/hello/hello.txt
echo "world" > /tmp/hello/world.txt

mkdir -p /tmp/world

declare -a my_array=()
my_array[0]="cp"
my_array[1]="/tmp/hello/*"
my_array[2]="/tmp/world"

# Run the command and it will fail
"${my_array[@]}"

Here is the error:

cp: cannot stat '/tmp/hello/*': No such file or directory

Is it possible for using (*) in the my_array? What's the correct syntax for implementing the 'cp /tmp/hello/* /tmp/world' with my_array?

Update:

There is a problem from @choroba's answoer, The $count and $sedond_item will be wrong:

mkdir -p /tmp/hello
echo "hello" > /tmp/hello/hello.txt
echo "world" > /tmp/hello/world.txt

mkdir -p /tmp/world

my_array=(cp)
my_array+=(/tmp/hello/*)
my_array+=(/tmp/world)

count=${#my_array[@]}
printf "%s\n" "count is: $count"

sedond_item="${my_array[1]}"
printf "%s\n" "second item is: $sedond_item"

Here is the output of @choroba's answoer:

count is: 4
second item is: /tmp/hello/hello.txt

But the $count and $sedond_item are correct in my original array:

mkdir -p /tmp/hello
echo "hello" > /tmp/hello/hello.txt
echo "world" > /tmp/hello/world.txt

mkdir -p /tmp/world

declare -a my_array=()
my_array[0]="cp"
my_array[1]="/tmp/hello/*"
my_array[2]="/tmp/world"

count=${#my_array[@]}
printf "%s\n" "count is: $count"

sedond_item="${my_array[1]}"
printf "%s\n" "second item is: $sedond_item"

Here is the output of original array:

count is: 3
second item is: /tmp/hello/*
command-line

2 Answers

  1. Best Answer

    I don't think you can - safely1 - do what you want to in bash.

    In bash (as well as POSIX sh and ksh), double quoting of parameter expansions (including array expansions like "{my_array[@]}" in shells that support them) prevents both word splitting and filename generation (aka globbing). On the other hand, unquoted expansions are subject to both word splitting and globbing (the so-called "split+glob" operation). In bash, you can turn off globbing using set -f (or equivalently set -o noglob) but AFAIK you can't turn off word splitting while leaving globbing on.

    Note that word splitting occurs before globbing, so it's not the expansion of /path/without/whitespace/* to /path/without/whitespace/name with whitespace that's the issue - it's the expansion of /path with whitespace/*.

    In zsh however, unquoted variable expansions are not subject to split+glob by default, and you can enable globbing separately using the ~ parameter expansion flag2.

    Note that in all cases, the RHS of an assignment like var=* or my_array[1]=/tmp/hello/* is not expanded even when unquoted.

    So in zsh for example (noting that zsh arrays are indexed from 1 not 0 as in bash):

     % typeset -a my_array
 % my_array[1]=ls
 % my_array[2]="my dir/*"
 % typeset -p my_array
typeset -a my_array=( ls 'my dir/*' )

 % ${my_array[@]}
ls: cannot access 'my dir/*': No such file or directory

    (same as quoted "${my_array[@]}" in both bash and zsh) but

     % ${~my_array[@]}
'my dir/hello'  'my dir/world'

    You can verify that the globbing is happening at expansion time by adding another file:

     % touch 'my dir/a new file'
steeldriver@steeldriver-virtualbox ~/dir
 % ${~my_array[@]}          
'my dir/a new file'  'my dir/hello'  'my dir/world'

    For your specific case I'd suggest adding a few safety measures - in particular using GNU mv's -t to set the target directory explicitly and -n to prevent accidental overwriting, and an additional argument -- to mark the end of options (which becomes important if the glob may expand to filenames starting with hyphens):

    #!/bin/zsh

typeset -a my_array

my_array[1]=mv
my_array[2]=-nt
my_array[3]=/tmp/world
my_array[4]=--
my_array[5]=/tmp/hello/*

${~my_array[@]}

    Although TBH if you are going to switch to zsh, you might consider using the contributed zmv module - which takes (quoted) glob expressions and expands them internally - in place of plain mv.

    1. by which I mean without using eval

    2. although note that ${~my_array[@]} turns on globbing during the expansion of every element of the array

    • 2

  2. Use the asterisk when populating the array, but don't populate it one element at a time:

    my_array=(cp /tmp/hello/* /tmp/world)
"${my_array[@]}"

    Or use the += operator to exapand the array:

    my_array=(cp)
my_array+=(/tmp/hello/*)
my_array+=(/tmp/world)
"${my_array[@]}"
    • 1